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| [261] | Flying triangulation—an optical 3D sensor for the motion-robust acquisition of complex objects |
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Svenja Ettl, Oliver J. Arold, Zheng Yang, Gerd Häusler |
| Applied Optics , 51(2), 281-289 (2012) |
Three-dimensional (3D) shape acquisition is difficult if an all-around measurement of an object is desired or if a relative motion between object and sensor is unavoidable. An optical sensor principle is presented—we call it “flying triangulation”—that enables a motion-robust acquisition of 3D surface topography. It combines a simple handheld sensor with sophisticated registration algorithms. An easy acquisition of complex objects is possible—just by freely hand-guiding the sensor around the object. Realtime feedback of the sequential measurement results enables a comfortable handling for the user. No tracking is necessary. In contrast to most other eligible sensors, the presented sensor generates 3D data from each single camera image. |
AO_Ettl_FlyTri.pdf
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| [260] | Limitations of optical 3D sensors |
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| Optical Measurement of Surface Topography , 23-48 (2011) , Richard Leach (Ed.), Springer, Berlin |
This chapter is about the physical limitations of optical 3D sensors. The ultimate limit of the measurement uncertainty will be discussed; in other words: “How much 3D information are we able to know?” The dominant sources of noise and how this noise affects the measurement of micro-scale topography will be discussed. Some thoughts on how to overcome these limits will be given. It appears that there are only four types of sensors, to be distinguished by the dominant sources of noise and how the physical measurement uncertainty scales with the aperture or working distance. These four types are triangulation, coherence scanning interferometry at rough surfaces, classical interferometry and deflectometry. 3D sensors will be discussed as communication channels and considerations about information-efficient sensors will be addressed. |
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GH_Leach_2011.pdf
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| [248] | "Flying Triangulation" – Acquiring the 360° Topography of the Human Body on the Fly |
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Svenja Ettl, Oliver J. Arold, Florian Willomitzer, Zheng Yang, Gerd Häusler |
| Proceedings of the International Conference on 3D Body Scanning Technologies , 279-284 (2010) , Lugano, Schweiz |
We introduce a novel optical measurement principle: “Flying Triangulation”. It fills an important gap in 3D metrology because it enables an acquisition of the topography of moving objects. The immunity against relative motion between object and sensor also allows for medical applications. An easy acquisition of complex objects is possible – just by freely hand guiding the sensor around the object. No tracking is necessary. We will present a “Flying Triangulation” sensor for the intraoral measurement of teeth and a sensor realization for the full 360° 3D acquisition of a person’s head. Parts of the body can be captured with high precision by comfortably guiding the sensor, with real-time control of the result. |
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SE_Lugano_FlyTri_2010.pdf
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| [246] | How precise is "Flying Triangulation" |
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Oliver J. Arold, Zheng Yang, Svenja Ettl, Gerd Häusler |
| DGaO-Proceedings, 111, A23 (2010) |
Flying Triangulation is a novel optical 3D measurement principle. It enables the acquisition of surface information by moving a hand-guided sensor freely around the object while taking a series of sparse 3D views. These partial views are automatically aligned by sophisticated algorithms. No external tracking systems are required. The high precision is exemplary presented for measurements of faces and teeth. |
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OA_DGaO_111_a23.pdf
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| [244] | 3D face scanning with "Flying Triangulation" |
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Florian Willomitzer, Zheng Yang, Svenja Ettl, Oliver J. Arold, Gerd Häusler |
| DGaO-Proceedings, 111, P18 (2010) |
Based on our new measurement principle "Flying Triangulation", we demonstrate a hand held 3D scanner for objects with a size of a few hundred millimeters. A specific application is the 3D measurement of human heads. The sensor can be freely moved around the object without requiring any external tracking. The resulting 3D model is displayed in real time. |
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FHW_DGaO_111_p18.pdf
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| [241] | Tuning Structured Illumination Microscopy (SIM) for the Inspection of Micro Optical Components |
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| [240] | Information efficient and accurate Structured Illumination Microscopy (SIM) |
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Alexander Kessel, Markus Vogel, Zheng Yang, Christian Faber, Markus C. Seraphim, Gerd Häusler |
| DGaO-Proceedings, 111, P9 (2010) |
With the concept of "structured illumination microscopy (SIM)", introduced at the DGaO-Conference 2009, it is possible to quantitatively acquire the 3D-topography of rough and smooth surfaces with extremely high longitudinal resolution (better than 10 nm for smooth surfaces). SIM is incoherent, information efficient and needs simple technology. By means of a high aperture the system is furthermore capable of measuring steep slopes up to 60 degrees, even for smooth objects. The acquired images have SEM-like quality.
These features make the sensor attractive to measure micro optical components. Optical components, however, often require a global accuracy better than 100 nm. This is difficult to achieve, because the global deviations depend on the field and on the slope of the surface. We present an error analysis of SIM and identify the major deviations. Methods to compensate for the inevitable technological imperfections will be discussed. We present SEM-like (quantitative) images of smooth and rough micro-objects. |
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AK_DGaO2010_p9_SIM-InformationEfficiency.pdf
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| [239] | Microdeflectometry and Structured Illumination Microscopy – New Tools for 3D-Metrology at Nanometer Scale |
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Gerd Häusler, Markus Vogel, Zheng Yang, Alexander Kessel, Christian Faber, Christoph Kranitzky |
| Proceedings Precision Interferometric Metrolog, ASPE 2010 Summer Topical Meeting, 49, 46-51 (2010) |
We will introduce two new 3D-sensors to measure the 3D-topography of smooth and rough surfaces. Both sensors allow for a depth (z-) sensitivity at the nanometer scale. The sensors use spatially and temporally incoherent illumination and are not based on interferometry (but may occasionally compete with - or at least complement - interferometry). They are robust and simple and (specifically µ-deflectometry) information theoretically efficient. With low noise and high depth of field they provide (quantitative 3D-) images with SEM-like quality. |
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ASPE_2010_Defl_u_SIM_ExAbstract.pdf
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| [238] | Information Efficient White-Light Interferometry |
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Ondrej Hybl, Gerd Häusler |
| Proceedings Precision Interferometric Metrology, ASPE 2010 Summer Topical Meeting, 49, 81-84 (2010) |
White light interferometry (WLI) is a precise and versatile tool to measure rough surfaces. However, it requires a big amount of raw data. Increasing demands on measurement speed and camera resolution urge us to reduce the necessary number of camera frames. In comparison to the acquisition of 2D images, where megapixels of data can be acquired “ready to use”, 3D images are calculated from big amount of 2D raw images. The number of necessary raw images is at least three for photometric stereo or fringe projection, but it might be several hundreds for white-light interferometry. It is obvious that industry would prefer a sensor that does not need to acquire hundreds of raw images for one single 3D map. |
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ASPE_2010_Hybl_Abstract.pdf
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| [237] | Microdeflectometry in transmission |
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Sandy Peterhänsel, Claus Richter, Christian Faber, Markus C. Knauer, Gerd Häusler |
| DGaO-Proceedings, 110, P24 (2009) |
We present a novel microscopic method that intrinsically measures local phase gradients of transparent objects. The method is based on "phase measuring deflectometry" [1] in transmission. Images similar to those achieved with differential interference contrast or with phase contrast are generated. However, the novel method displays some additional new features: the images display quantitative data about the lateral variation of the optical path length; the sensitivity reaches the physical limit: very small variations of the refractive index can be measured . Moreover, the method is simple (no interference !). Micro-deflectometry in transmission has the potential to compete with established methods to acquire phase object information. |
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SP_2009_DGaO_110_P24_Micro_Deflectometry_Transmission.pdf
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| [236] | Object tilt - a source of systematic error in transmission deflectometry |
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Anton Lopatin, Claus Richter, Christian Faber, Markus C. Knauer, Gerd Häusler |
| DGaO-Proceedings, 110, P23 (2009) |
Phase measuring Deflectometry (PMD) utilises the deflection of rays impinging at an object, to acquire information about the local gradient of an object surface (in reflection) or the local gradient of the optical path length (in transmission). PMD in transmission displays an interesting difficulty: in order to get the correct wedge angle from the deflected rays, we need to know the local tilt of the object, which, in general, cannot be determined. In other words: a planar glass window will appear as a wedge, if it is measured in a tilted orientation. Although the systematic error introduced by a tilt is commonly small, it severely disturbs the ultra-precise measurement of planar objects (car window glasses) or lenses. We will discuss the origin of the systematic error and present a measuring scheme to overcome the problem. |
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AL_2009_DGaO_110_P23_Object_Tilt_Transmission_Deflectometry.pdf
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| [235] | A new registration method to robustly align a series of sparse 3D data |
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Oliver J. Arold, Zheng Yang, Svenja Ettl, Gerd Häusler |
| DGaO-Proceedings, 110, P20 (2009) |
Optical measurement tasks often require an acquisition of several partial 3D views to collect complete 3D information of an object surface. We consider a sensor that acquires the surface information by taking a series of sparse partial 3D views while being freely moved around the object. In order to obtain a dense 3D model of the surface an alignment of all partial views is required. Existing methods usually detect common surface features and map them onto each other. However, in case of sparse data these methods fail, because insufficient or no neighborhood surface information of points is available to find common features. We propose a method that is specifically tailored for the robust registration of sparse 3D data. In a first step, consecutive images are aligned successively. The approach focuses on detecting corresponding points instead of surface features. The successive registration leads to an accumulation of the error along the series of views. Therefore, in a second step, the global registration error is minimized. The combination of these two steps provides a robust registration method. In this paper we will present the new registration method and give some results. |
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OA_DGaO110_P20_FlyTri_registration.pdf
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| [234] | A 3D-Sensor for intraoral metrology |
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| [232] | Ultrafast 4-Megapixel White-Light-Interferometry |
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Reinhard Groß, Ondrej Hybl, Peter Ettl, Benno Knapp, Gerd Häusler |
| Proceedings of the 110th Annual Meeting of the DGaO (2009) , Brescia, Italy |
White-Light interferometry (WLI) requires a big amount of raw data, which contradicts the demands for increasing measurement speed and bigger number of pixels. Meanwhile, 4 Megapixel cameras are available with a continuous frame rate greater than 100 frames per second. With conventional sampling, this would allow a measurement speed of 'only' 20µm/sec. We will demonstrate that this limit can be overcome by factor of about 30. We achieve a measurement speed of more then 500µm/sec by a novel undersampling scheme. We present results from electronics and automotive applications. |
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RG_DGaO2010_p17.pdf
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| [231] | "Flying Triangulation" - a new optical 3D sensor enabling the acquisition of surfaces by freehand motion |
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Svenja Ettl, Oliver J. Arold, Peter M. Vogt, Ondrej Hybl, Zheng Yang, Weiguo Xie, Gerd Häusler |
| DGaO-Proceedings, 110, A13 (2009) |
In order to obtain complete 3D surface information of an object it is often necessary to acquire many partial 3D views. For this purpose, the sensor has to be moved (e.g. for sculptures, rooms). In many other cases a motion of the object relative to the sensor is unintended but inevitable (e.g. for medical purposes). Nearly all existing optical 3D sensors either lack an easy handling or require a standstill during the acquisition of a single partial 3D view. This makes such measurements elaborate or even impossible. We demonstrate an optical 3D measurement system that overcomes the mentioned difficulties. It combines a simple (single-shot) sensor and sophisticated algorithms. A series of sparse 3D views is acquired while the hand held sensor moves freely around the object. In order to get a dense 3D model of the surface the views are aligned by specially developed algorithms. In this paper we will present this new 3D sensor and show some measurement examples. |
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SE_DGaO110_A13_FlyTri_general.pdf
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| [230] | 3D-microscopy with large depth of field |
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Christoph Kranitzky, Claus Richter, Christian Faber, Markus C. Knauer, Gerd Häusler |
| DGaO-Proceedings, 110, A12 (2009) |
We introduce a simple attachment to a common microscope enabling it to measure the microtopography of both rough and smooth samples and thus combining the inherent high lateral resolution of the microscope and depth information. We achieve a depth resolution better than 10 nanometers and a depth of field more than 100 times the Rayleigh depth. Even steep slopes of more than 60 degrees become accessible (dependent on the aperture). The method is derived from 'Phase measuring micro-deflectometry' which is a novel tool to measure the slope of reflective structures on a microscopic scale. With the microscopic lateral resolution and the very large depth of field, as well as a low noise level, the images display 'SEM-like' features. |
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CWK_DGaO110_a12_SIM_principle_2009.pdf
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| [229] | Can deflectometry work in presence of parasitic reflections? |
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Christian Faber, Markus C. Knauer, Gerd Häusler |
| DGaO-Proceedings, 110, A10 (2009) |
Phase Measuring Deflectometry (PMD) is a meanwhile established method to facilitate the measurement of specular freeform surfaces with high dynamical range. However, for transparent objects like progressive eyeglass lenses, this metrology suffers from one severe limitation: the parasitic reflection at the rear side of the specimen renders the conventional phase evaluation impossible. Therefore, such objects currently have to be specifically prepared for deflectometric measurements by roughening or blackening the rear side. In this talk, different approaches to overcome this major drawback are introduced and compared. The performance of these methods is analyzed with respect to the attainable accuracy and measuring speed, underlining aspects of information efficiency. We present first complete measurements of the refractive power of surfaces for progressive lenses whose rear sides have not been blackened or treated in any other special way. |
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CF_2009_DGaO_110_A10_Deflectometry_Parasitic_Reflections.pdf
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| [227] | Machine-Integrated Measurement of Specular Free-Formed Surfaces Using Phase-Measuring Deflectometry |
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Claus Richter, Martin Kurz, Markus C. Knauer, Christian Faber, Evelyn Olesch, Gerd Häusler, Dirk Oberschmidt, Jörg Eßmann, E. Uhlmann |
| Proc. euspen International Conference (2009) , San Sebastian |
We present first results of a project with the long-term goal of performing optical measurements of ultra precision turned objects within the turning machine. Whereas ultra precision turning machines facilitate the manufacturing of optical free-formed parts, the task of measuring these objects is not yet solved satisfactorily. Moreover, an optical measurement within the machine would be of great advantage concerning a possible feedback to the turning process. Phase-measuring deflectometry has the potential to solve these tasks, but the system has to be adapted to provide the necessary dynamic range and to cope with the limited installation space within the system. We present measuring results of ultra precise turned parts manufactured on a 5-axis ultra precision machine. The surface of these objects displays a local slope up to 30°. Furthermore, the potential for future integration of such a measurement system into an ultra precision lathe is demonstrated. |
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CR_Euspen_2009.pdf
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| [226] | “Flying Triangulation”: A motion-robust optical 3D sensor principle |
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Svenja Ettl, Oliver J. Arold, Peter M. Vogt, Ondrej Hybl, Zheng Yang, Weiguo Xie, Gerd Häusler |
| Fringe 2009, The 6th International Workshop on Advanced Optical Metrology, 768-771 (2009) , W. Osten and M. Kujawinska (Ed.), Springer |
The complete and precise acquisition of a complex object surface can be an elaborate or even impossible task with existing sensors. First, to entirely measure the surface the sensor needs to acquire partial 3D views from different positions. Thus, the sensor has to be moved, sometimes hundreds of times or even more (e.g. for measuring sculptures or architecture). Second, sometimes a motion of the object relative to the sensor is unintended but inevitable (e.g. for medical purposes). Thus, the sensor has to acquire the single 3D views fast enough to avoid a loss of precision caused by motion. So far, most existing optical 3D sensors lack this property. We present a new optical 3D measurement system we call "Flying Triangulation" that overcomes the mentioned difficulties.
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SE_Fringe_2009_FlyTri_general.pdf
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| [225] | Deflectometry: 3D-Metrology from Nanometer to Meter |
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Gerd Häusler, Markus C. Knauer, Christian Faber, Claus Richter, Sandy Peterhänsel, Christoph Kranitzky, Klaus Veit |
| Fringe 2009, The 6th International Workshop on Advanced Optical Metrol, 416 - 421 (2009) , W. Osten and M. Kujawinska (Ed.), Springer-Verlag, Berlin, Heidelberg, New York |
Deflectometry offers a wide spectrum of applications. The intrinsic features of deflectometry made this technique popular over the last years. Deflectometry enables to measures the local slope of specularly reflecting objects with high information efficiency. It is possible to measure structures quantitatively in the nanometer regime. Due to incoherent illumination the data display no coherent noise. The standard setup is suited for measurements in reflection. Applications have been the measurement of the surfaces of eyeglass lenses, mirrors or reflectors. As well, the measurement of the reflectionoptics of car windshields had been an interesting application. Recently we adapted deflectometry for measurements in transmission at macroscopic and microscopic scale to expand the possible range of applications. |
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GH_2009_Fringe_Deflectometry.pdf
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| [224] | Measurement of the shape of objects by the interferometry with two wavelengths |
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Pavel Pavlicek, Gerd Häusler |
| Fringe '09, pp. 339-344 (2009) , W. Osten, M. Kujawinska (Ed.), Springer-Verlag Berlin, Heidelberg, New York, Stuttgart |
White-light interferometry is an established method for the measurement of geometrical shape of object with smooth or rough surface. One of the disadvantages of white-light interferometry is that the required broadband light sources suffer from a low luminance. This shows up when the shape of object with a weakly reflecting surface is measured or when the measured area is large. One way to overcome this disadvantage is to replace the broadband light source by two (or more) lasers with various wavelengths. If the broadband light source is replaced by two lasers with various wavelengths, a typical beat pattern arises at the output of the interferometer instead of white-light interferogram. The beat pattern can be used for the determination of the position of the object's surface in a similar way as white-light interferogram. Unlike to white-light interferogram, the beat pattern is periodic and therefore the unambiguity range is limited. |
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PP_Fringe2009.pdf
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| [223] | Deflektometrie macht der Interferometrie Konkurrenz |
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Markus C. Knauer, Claus Richter, Ondrej Hybl, Jürgen Kaminski, Christian Faber, Gerd Häusler |
| tm - Technisches Messen, 76, 175-181 (2009) , (Ed.), Oldenbourg, München |
Deflectometry is a new method that was developed during the last years to measure specular surfaces. With this method we can measure local height variations in the nanometer regime on free-form surfaces. To understand the benefits of deflectometry we study the physical limits and information theoretical aspects of the method. Finally, we demonstrate the versatility of deflectometry by presenting several possible applications. |
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MCK_teme_2009.pdf
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| [222] | Phasenmessende Deflektometrie |
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Markus C. Knauer, Claus Richter, Christian Faber, Gerd Häusler |
| Jahrbuch 2008 Optik und Feinmechanik, 141-153 (2009) , Wolf-Dieter Prenzel (Ed.), Schiele & Schön |
Die Phasenmessende Deflektometrie (PMD) ist ein spezielles deflektometrisches Messverfahren, das sich zur schnellen und präzisen Vermessung spiegelnder Freiformflächen eignet. Auf Basis des Verfahrens lassen sich Sensoren mit Messfeldern von 0,1 mm bis über 1000 mm konstruieren. Das Messprinzip kann sowohl in Reflexion zur Vermessung spiegelnder Oberflächen – und damit zur Analyse einzelner optischer Grenzflächen – als auch in Transmission zur Analyse der gesamten optischen Wirkung eines (in diesem Fall transparenten) Bauteils eingesetzt werden. [...] Im Folgenden geben wir einen Überblick über die prinzipielle Funktionsweise und die Eigenschaften der Deflektometrie im Allgemeinen sowie der Phasenmessenden Deflektometrie im Speziellen. Wir gehen auf die physikalischen Grenzen ein und zeigen typische Anwendungen. |
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| [221] | Information Efficient White-Light Interferometry |
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Ondrej Hybl, Andreas Berger, Gerd Häusler |
| DGaO-Proceedings, 109, A29 (2008) |
White light interferometry (WLI) is a precise and versatile tool to measure smooth and rough surfaces. However, WLI requires a big amount of raw data (often hundreds of camera frames). Increasing demands on measurement speed and camera resolution urge us to reduce the necessary number of camera frames. We introduce three novel methods to achieve this goal: We first demonstrate that it is principally possible to reconstruct the correlogram envelope from only 10 exposures, nearly independent from the object depth. Another method to improve the information efficiency is to adapt the illuminating wave to the object shape. As an example, we demonstrate the measurement of cylinders and cones. We use a properly adapted conical mirror in the object arm of the interferometer. Light rays are directed perpendicular to the measured cylindrical or conical surface. The alignment of the object is uncritical and sub-lambda-accuracy can be achieved. The third method is to adapt the reference wave to the object shape. A simple solution is to put an (optically rough!) master object in the reference arm. This enables an extremely fast quantitative comparison of master and test object. |
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OH_DGaO109_a29_Inform.pdf
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| [220] | Measuring the refractive power with deflectometry in transmission |
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Markus C. Knauer, Claus Richter, Gerd Häusler |
| DGaO-Proceedings, 109, A24 (2008) |
We apply "Phase-measuring Deflectometry" (PMD) to the high-precision measurement of refractive power maps in transmission. As is the case for the measurement in reflection a sinusoidal fringe pattern is observed - however in the transmitted light. The local prismatic action of the object under test causes a phase offset in the observed picture, which can be determined by means of well-known phase-shifting techniques. Based on the measured values, the surface power can be determined with an accuracy better than one milli-diopter. We show experiments and discuss the algorithms and the error tolerance. The system supplies traceable data without the need for a special calibration object. The robust and non-expensive method has several possible applications, e.g. the measurement of car glass windows and of eyeglass lenses. |
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MCK_DGaO109_a24_trans.pdf
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| [219] | Sub-micron profilometry on macroscopic free-form surfaces |
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Jürgen Kaminski, Gerd Häusler |
| DGaO-Proceedings, 109, A22 (2008) |
An important application of deflectometry is the measurement of local (3D) surface details (e.g. scratches or milling grooves) that are only a few nanometers deep. However, these details are only visible if they can be separated from the global height variation: some objects may have a dynamic range of 1,000,000:1 or more. We present a new method for fast, quantative reconstruction of height profiles from deflectometric data. The method relies on the evaluation of curvature maps, where small details are easily detectable. After subtracting the bias curvature the profile is reconstructed by numerical integration. The accuracy of the height profile only depends on the uncertainty and the lateral resolution of the sensor. We achieve an accuracy of 10-50 nm on a measuring field of 70 mm, which we will demonstrate by several mesurements. |
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JNK_DGaO109_a22_Profile.pdf
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| [217] | Microdeflectometry—a novel tool to acquire three-dimensional microtopography with nanometer height resolution |
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Gerd Häusler, Claus Richter, Karl-Heinz Leitz, Markus C. Knauer |
| Optics Letters 33, 4, 396-398 (2008) |
We introduce "microdeflectometry," a novel technique for measuring the microtopography of specular surfaces. The primary data are the local slope of the surface under test. Measuring the slope instead of the height implies high information efficiency and extreme sensitivity to local shape irregularities. The lateral resolution can be better than 1 µm, whereas the resulting height resolution is in the range of 1nm. Microdeflectometry can be supplemented by methods to expand the depth of field, with the potential to provide quantitative 3D imaging with scanning-electron-microscope-like features. |
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GHCRKHLMCK_2008_Microdeflectometry_OL.pdf
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| [215] | Shape reconstruction from gradient data |
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Svenja Ettl, Jürgen Kaminski, Markus C. Knauer, Gerd Häusler |
| Applied Optics, 47, No. 21, 2091-2097 (2008) , OSA |
We present a generalized method for reconstructing the shape of an object from measured gradient data. A certain class of optical sensors does not measure the shape of an object but rather its local slope. These sensors display several advantages, including high information efficiency, sensitivity, and robustness. For many applications, however, it is necessary to acquire the shape, which must be calculated from the slopes by numerical integration. Existing integration techniques show drawbacks that render them unusable in many cases. Our method is based on an approximation employing radial basis functions. It can be applied to irregularly sampled, noisy, and incomplete data, and it reconstructs surfaces both locally and globally with high accuracy. |
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SEJNKMCKGH_Integration_AO2008.pdf
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| [214] | Fast and robust 3D shape reconstruction from gradient data |
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Svenja Ettl, Jürgen Kaminski, Evelyn Olesch, Hans Strauß, Gerd Häusler |
| DGaO-Proceedings, 108, P26 (2007) |
Sensors based on deflectometry measure the local slope of a surface. The object shape can then be reconstructed by spatial integration. Recently, we presented a method employing radial basis functions (RBFs) which accurately reconstructs both local details and the global shape. However, for large data sets the method requires a domain decomposition technique which may introduce error propagation. Further, it may be time consuming. Often the data is acquired on a regular grid. For this case, we present a method employing B-splines. It yields an accuracy similar to the RBF approach while being faster and more robust against error propagation. |
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SE_DGaO07_fast.pdf
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| [213] | Robust automatic coarse registration of specular free-form surfaces |
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Jürgen Kaminski, Matthias Struck, Tobias Maier, Svenja Ettl, Gerd Häusler |
| DGaO-Proceedings, 108, A2 (2007) |
Many industrial applications of optical 3D sensors require the alignment (so-called “registration”) of different 3D data sets into one common coordinate system. This is necessary e. g. for variance analysis or to combine several partial measurements of an object into a complete 3D view. Smooth specular surfaces, however, have no prominent features like edges or corners. That makes registration difficult.
We present a promising registration method based on Hough transformation. It is robust against small shape deviations, outliers, and noise, and it does not require user interaction. |
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JNK_DGaO07_robust.pdf
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| [212] | Zauberspiegel, Brillengläser und Wasserhähne - alte Probleme neu beleuchtet |
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Markus C. Knauer |
| DGaO-Proceedings, 108, H2 (2007) |
„Chinesische Zauberspiegel“ sehen auf den ersten Blick wie gewöhnliche Metallspiegel mit kunstvoll verzierter Rückseite aus. Lässt man jedoch vom Spiegel reflektiertes Licht auf einen Schirm fallen, so erscheint erstaunlicherweise das Muster der Rückseite. Der Effekt beruht auf kleinen, lokalen Neigungsvariationen der polierten Fläche.
Für die Messung solcher Neigungsvariationen auf spiegelnden Oberflächen eignet sich besonders die in den letzten Jahren wiederentdeckte Deflektometrie. Sie ist einfach, schnell, hochempfindlich und robust (inkohärent). Mit der Deflektometrie lassen sich auch stark asphärische blanke Freiformflächen vermessen, was bis vor kurzem nur mit hohem Aufwand lösbar war.
Wir geben einen Überblick über die deflektometrischen Sensoren mit Ihren Möglichkeiten und Grenzen. Es gibt ein breites Spektrum möglicher Anwendungen – von Kontaktlinsen bis zu Autoscheiben und von Wafern bis zu Wasserhähnen. |
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MCK_DGaO07_108-H2.pdf
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| [211] | Herstellung eines Mikrokegelspiegels für die optische Messtechnik: Im Spiegelkabinett |
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Martin Kurz, Ondrej Hybl, Dirk Oberschmidt, Gerd Häusler |
| Mikroproduktion , 3, 27-29 (2007) , (Ed.), Carl Hanser Verlag, München |
Dank optischer Verfahren funktioniert die Formmessung von Bauteilen schnell, berührungslos und genau. Ein Kohärenz-Radar ermöglicht die Messung auch komplizierter Bauteile mit umlaufenden Flächen und sehr steilen Flanken wie beispielsweise Zylinder oder Kegel. Die für den Messaufbau benötigten Spiegel sind für große Durchmesser in reicher Auswahl erhältlich. Für kleine Innendurchmesser jedoch, wie sie zum Beispiel bei Einspritzdüsen oder Nadelventilen vorkommen, sind extra angepasste Spiegelkomponenten nötig. Die Ultrapräzisions-Zerspanung ist die geeignete Methode zur Herstellung derartiger Spiegel. |
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| [208] | Generalized Hermite interpolation with radial basis functions considering only gradient data |
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Svenja Ettl, Jürgen Kaminski, Gerd Häusler |
| Curve and Surface Fitting: Avignon 2006, pp. 141-149 (2007) , A. Cohen, J.-L. Merrien and L. L. Schumaker (Ed.), Nashboro Press, Brentwood, TN |
The task is to recover a function z from R2 to R, given only its gradient data at a set of points. This is an important problem in optical metrology – where the surface of an object needs to be reconstructed from its measured slopes – which still lacks a satisfying solution. We solve the problem employing a Hermite interpolation method based on radial basis functions. Our approach has the following advantages: The data can be arbitrarily scattered and its dynamic range can be large. Further, the method is robust against error propagation. However, the challenge is the data size: A common optical data set consists of about two million elements. This makes a direct solution impossible. To overcome this limitation, we developed a partition of unity method specifically tailored for this task. |
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SE_JNK_GH_CaS2007.pdf
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| [210] | Segmentation Based Fast Registration of Free Form Surfaces in the Euclidean Space |
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Tobias Maier, Gerd Häusler |
| Proceedings of VMV, 17-24 (2006) , L. Kobbelt, T. Kuhlen, T. Aach, R. Westermann (Ed.), Aachen |
The task of registration of free form surfaces comes up in various contexts, like object reconstruction or localization of objects. Often it should be close to ”real time”. The process is divided in two different steps: Coarse and Fine registration. Whereas the latter one is well established in form of the ICP-Algorithm, the first one is still often done by user interaction. ”Coarse” means that an initial estimation for the transformation has to be found in order to start the ICP. A lot of strategies have been developed to perform coarse registration automatically. This contribution well overcomes some disadvantages of a prior approach that deals with objects containing planar surface parts (”technical” objects). The complete algorithm is described in terms of graph theory and tested with data acquired by an optical range sensor. |
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TM_vmv06.pdf
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| [207] | Automatic Coarse Registration of 3D-Surfaces by Information Theoretic Selection of Salient Points |
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Nikolaus Schön, Gerd Häusler |
| Applied Optics, Vol. 45, 6539-6550 (2006) |
We describe a new method to register surface data measured by optical 3-D sensors from various views of an object. With our method, complete 3-D models of objects can be generated, without user interaction.
Circumferential acquisition of 3-D objects is done by taking several views from different directions. In order to generate a complete 3-D-model, the views have to be aligned to each other. This process is called registration, and is commonly done interactively by searching for so-called “corresponding points” in the different views and by using these points to calculate the appropriate rotation and translation. Our approach is based on automatically finding points that are “eye-catching” or “salient”, compared to other surface points. We derive a quantitative measure of point salience and a feature definition for free form surfaces by introducing a concept to measure pragmatic information. Experiments confirm that our salient points can be robustly located on general free-form surfaces, even if there are no corners or edges. Furthermore, the neighborhoods of the salient points are highly distinguishable from each other. This results in a large reduction of the complexity of the subsequent geometric matching. The computing time is a few seconds only. We present results from various fields of application. |
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Schoen_Haeusler_Complete.pdf
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| [206] | Faster and better white light interferometry |
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Bernhard Wiesner, Andreas Berger, Reinhard Groß, Ondrej Hybl, Claus Richter, Gerd Häusler |
| Proceedings of ODIMAP V, 216-221 (2006) , (Ed.), Madrid |
Although well established, white light interferometry (WLI) suffers from several limitations, which come into play if the requirements for speed and accuracy increase. We introduce some new modifications of the coherence radar that - to a great extent - overcome these difficulties. |
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Haeusler_Richter_Hybl_Odimap2006.pdf
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| [205] | Reduced Measurement Uncertainty of White-Light Interferometry on Rough Surfaces |
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Reinhard Groß, Ondrej Hybl, Claus Richter, Bernhard Wiesner, Gerd Häusler |
| Speckle 06, Speckles, From Grain to Flowers, 6341 (2006) , (Ed.), Proc. SPIE, Nimes |
In white-light interferometry at rough surfaces ("Coherence radar") the measuring uncertainty is physically limited by the arbitrary phase of the individual speckle interferograms. As a consequence, the standard deviation of the measured shape data is inevitably given by the (optically unresolved) roughness of the surface. The statistical error in each measuring point depends on the brightness of the corresponding speckle; a dark speckle yields a more uncertain measurement than a bright one. If the brightness is below the noise threshold of the camera, the measurement fails completely and an outlier occurs. We present a new method to significantly reduce the measuring uncertainty and the number of outliers. We achieve this by generating several statistically independent speckle patterns, by use of different directions of the illumination. We evaluate the different measurements and select the best measurement or assign more weight to brighter speckles. |
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RG_CR_OH_GH_Speckle2006.pdf
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| [204] | Endoskopische 3D-Rekonstruktion mit kohärenztheoretisch optimierter Beleuchtung |
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Antonia Popp, Frank Wolfsgruber, Ingo Scholz, Gerd Häusler |
| DGaO-Proceedings, 107, B1 (2006) |
Es wird gezeigt wie groß die minimale durch kohärentes Rauschen bedingte Messunsicherheit bei der endoskopischen 3D-Vermessung eines Hohlraums ist.
Wir stellen eine modifizierte Endoskopbeleuchtung vor, mit deren Hilfe genauere und dichtere 3D-Punktewolken rekonstruiert werden können. |
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popp_dgao_2006.pdf
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| [203] | Höhe, Neigung oder Krümmung? |
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Markus C. Knauer, T. Bothe, Svenja Lowitzsch, W. Jüptner, Gerd Häusler |
| DGaO-Proceedings, 107, B30 (2006) |
Optische Herstellungstoleranzen werden üblicherweise als Höhenabweichungen angegeben. Mit der Deflektometrie stehen aber seit kurzem Verfahren zur Verfügung, um die lokale Neigung von blanken Oberflächen vollflächig und mit einer lokalen Unsicherheit von weniger als 1 arcsec zu messen. Zwar kann man durch zeitaufwändige Integration auch Höhendaten erzeugen, diese sind aber wegen unvermeidlicher Kalibrierfehler global ungenau (im 1µm-Bereich). Deshalb erscheint es sinnvoll, Neigungsdaten oder gar Krümmungsdaten anstelle von Höhendaten zu verwenden. Ein gutes Beispiel hierfür sind Gleitsichtbrillengläser: Für die strahlenoptische Rechnung wird die lokale Neigung der Fläche benutzt. Lageabweichungen (im 1µm-Bereich) wirken sich auf das Ergebnis nicht aus. Will man jedoch den Herstellungsprozess überwachen, so ist die Kenntnis der Höhe wichtig. |
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MCK_NeigungHohe_DGaO1072006.pdf
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| [202] | Ein neues Mess-System für die Echtzeitmessung der Achsfluchtung |
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Claus Richter, Gerd Häusler |
| DGaO-Proceedings, 107, P41 (2006) |
Beim „Rotationsreibschweißen“ wird ein Bauteil mit einem zweiten verschweisst, indem es bei hoher Umdrehungszahl mit hoher Kraft auf das feststehende zweite Bauteil gepresst wird. Die Technologie wird insbesondere beim Triebwerksbau (Luftfahrtindustrie) eingesetzt. Um die engen Fertigungstoleranzen einzuhalten, müssen die zu fügenden Bauteile vor dem Schweißprozess ausgerichtet werden. Das von uns vorgestellte Messsystem kann den Achsversatz im Millisekundentakt messen, und zwar mit einer Unsicherheit von weniger als 2 µm, und den Winkelversatz genauer als 2 arcsec. Das System besteht aus einem modifizierten Spiegel, der im rotierenden Futter eingebaut ist. Der Spiegel wird vom festen Futter beleuchtet und beobachtet. Aus dem Kamerabild kann man sowohl den Winkelversatz als auch den lateralen Versatz in Echtzeit errechnen. Das Verfahren kann für verschiedene Werkzeugmaschinen adaptiert werden. |
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CR_Fluchtung_DGAO107_2006.pdf
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| [201] | How much 3D information are we allowed to know and how much may a 3D sensor cost? |
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Svenja Lowitzsch, Gerd Häusler |
| Proceedings of ICO Topical Meeting on Optoinformatics/Information Photonics 2006 (2006) |
We will discuss the questions stated in the title from an information-theoretical point of view and we will present optical sensors which – under these information-theoretical considerations – cost only little. |
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SE_StPetersburg06_ICO.pdf
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| [187] | 3D sensor zoo – Species and natural habitats |
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Markus C. Knauer, Claus Richter, Gerd Häusler |
| Laser Technik Journal, 3(1), 33-37 (2006) , Wiley-VCH, Weinheim |
Optical 3D Sensors provide a fast non-destructive possibility to obtain the three-dimensional shape of a huge variety of objects. In this paper we will give an overview of some important sensor principles and their limits as well as some critical points to pay attention to when choosing a sensor. |
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| [186] | Weichgewebemodellierung durch Flächeninterpolation heterogen verteilter Messdaten |
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Sylvia Wilharm, Tobias Maier, Michaela Benz, Gerd Sußner, Svenja Lowitzsch, Gerd Häusler, Günther Greiner |
| Proceedings Bildverarbeitung für die Medizin 06, 191-195 (2006) , Heinz Handels, Jan Ehrhardt (Ed.) |
In vielen Operationssituationen muss der Chirurg trotz Weichgewebeschwellung im Eingriffsgebiet eine Prädiktion des postoperativen Zustands treffen. Zur Unterstützung des Arztes kann die Schwellung anhand des Volumens zwischen den Gewebeflächen von Haut und Knochen quantifiziert werden. In diesem Beitrag wird eine Methode vorgestellt, die mittels Gewebekonturen aus 2D-Ultraschallbildern intraoperativ eine Weichgewebemodellierung durchführt. Dies geschieht anhand einer analytischen Flächenbeschreibung der heterogen verteilten, fehlerbehafteten Messdaten. Die verwendeten Methoden basieren einerseits auf Interpolation mit radialen Basisfunktionen kombiniert mit Glättungsmaßnahmen, andererseits werden Approximationsmethoden mit Polynomen und radialen Basisfunktionen untersucht. Die aus Haut- und Knochenkonturen gewonnenen Ergebnisse der Interpolation werden denen der Approximationen gegen¨ubergestellt. |
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Wilharm_BVM2006.pdf
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| [185] | Automatische Segmentierung der Gewebegrenzen in 2D-Ultraschalldaten aus der Mund-, Kiefer- und Gesichtschirurgie |
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Sebastian Göb, Gerd Häusler, F.W. Neukam, Emeka Nkenke, Walter Kullmann, Thomas Wittenberg, Svenja Lowitzsch, Michaela Benz, Tobias Maier |
| Proceedings Bildverarbeitung für die Medizin 06, 176-180 (2006) , Heinz Handels, Jan Ehrhardt (Ed.) |
Es soll ein Modell der Gewebeschwellung bei Operationen im Gesichtsbereich erstellt werden. Zur Berechnung des Modells werden zunächst Daten mit einem optischen 3D-Sensor, sowie einem Ultraschallsensor akquiriert. Für den Modellierungsprozess ist es notwendig, die Haut- und die Knochengrenze aus den zweidimensionalen Ultraschallschnittbildern zu segmentieren. Die vorliegende Arbeit stellt ein vollautomatisches und robustes Verfahren zur Segmentierung der Konturen von Haut und Knochen vor. |
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Goeb_BVM2006.pdf
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| [192] | Automatic Coarse Registration of 3D Surfaces |
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Nikolaus Schön, Gerd Häusler |
| Vision, Modeling and Visualization 2005 Proceedings, 171-175 (2005) , Greiner, Hornegger, Niemann, Stamminger (Ed.), infix |
We describe a new method to register surface data measured by optical 3D sensors from various views of an object. Circumferential acquisition of 3D objects is done by taking several views from different directions. The views first have to be aligned to each other. This process is called registration, and is commonly done by searching for so-called “corresponding points” in the different views and by using these points to calculate the appropriate rotation and translation. Our approach is based on looking for points that are “eye-catching” or “salient”, compared to other surface points. We introduce a concept to quantify point salience by an information entropy measure. Experiments confirm that our salient points can be robustly located on general free-form surfaces, even if there are no corners or edges. Furthermore, the neighborhoods of the salient points are encoded as highly distinguishable feature vectors. This leads to a strong reduction of the complexity of the subsequent geometric matching. The computing time is a few seconds only. We present results from various fields of application. |
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KS_AutomaticCoarseRegisteation_VMV05.pdf
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| [191] | How to localize 3D-views in space? |
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Nikolaus Schön, Gerd Häusler |
| DGaO Proceedings, 106, A7 (2005) , (Ed.) |
A full 360° virtual 3D-view of an object is commonly put together from many different overlapping 3D-measurements. The task of putting this puzzle automatically together (“coarse registration”), is still a great challenge - although a child can do it. How does our brain manage the coarse registration? Obviously, we look for areas or points with big “saliency”, points that are eye-catching. We introduce an information theoretical concept, to find and mark those “eye-catching” points. The concept uses “pragmatic information”, which tells us, how useful the information for the specific task is. This pragmatic information allows a quantitative judgement about the value of different eye-catching points, for the registration of the data. The concept is implemented and we demonstrate its ability to reliably register 3D-views of a wide range of objects, within a few seconds. |
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NS_DGaO2005_a7.pdf
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| [189] | Highly improved measurement speed of white light interferometry |
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Claus Richter, Gerd Häusler |
| DGaO-Proceedings, 106, A4 (2005) , (Ed.) |
White-light interferometry is a well established optical sensor principle for shape measurements. It provides high accuracy on a great variety of surface materials. However, the scanning time of common systems limits the field of applications. We present a novel solution to reduce the scanning time significantly. |
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CR_DGaO05_highly.pdf
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| [188] | Shape reconstruction of 3d-objects from noisy slope data |
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Svenja Lowitzsch, Jürgen Kaminski, Gerd Häusler |
| DGaO Proceedings, 106, A22 (2005) , (Ed.) |
A specific class of 3d-sensors measures the local slope of an object surface instead of the local height or “shape”. Examples of those sensor principles are shape from shading, shearing interferometry, differential phase contrast, and deflectometry [1]. Those sensors show very high information efficiency [2] (since the measurement channel does not transmit the stand-off distance). But how can we reconstruct the shape from the slope data (the manufacturers of aspherical eye-glasses demand this, for example)? This is a challenging task if we want to exploit the complete information delivered by the sensor. One has to deal with noisy slope data which even might contain holes. Standard methods mostly cannot cope with these problems. We present a new method based on radial basis functions which yields a global shape reconstruction and can handle scattered data with holes. [1] M. Knauer, J. Kaminski, G. Häusler; Absolute Phasenmessende Deflektometrie, DGaO Proceedings, 2004 [2] C. Wagner, G. Häusler; Information theoretical optimization for optical range sensors, Applied Optics 42, 2003. |
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SL_DGaO05_shape_recon.pdf
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| [184] | Vision and Modeling of Specular Surfaces |
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Svenja Lowitzsch, Jürgen Kaminski, Markus C. Knauer, Gerd Häusler |
| Vision, Modeling and Visualization 2005 - Proceedings, 479-486 (2005) , G. Greiner, J. Hornegger, H. Niemann, M. Stamminger (Ed.), Akademische Verlagsgesellschaft Aka GmbH, Berlin |
We present the combination of a sensor based on “Phase-Measuring Deflectometry” and a new numerical algorithm to obtain the shape of specular free-form surfaces. The sensor measures the local slope of the surface which then is used to reconstruct the object’s shape. The sensor is calibrated and yields absolute slope data. We solved the inherent ambiguity of deflectometric sensors using a novel stereo method for specular surfaces. The presented reconstruction algorithm interpolates the slope data and thus yields an analytic representation of the surface. It can deal with highly curved objects, is stable against noise, and does not require equidistantly sampled data. With the combination of the sensor and the robust numeric algorithm we are able to obtain the global shape of specular free-form surfaces with micron accuracy. Local details can even be measured in a range of a few nanometers depth variation. |
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SL_VMV2005_specular_surfaces.pdf
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| [183] | A simple and efficient optical 3D-Sensor based on Photometric Stereo ("UV-Laser-Therapy") |
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Frank Wolfsgruber, Christian Rühl, Jürgen Kaminski, Ludmila Kraus, Gerd Häusler, Ralf Lampalzer, E. B. Häußler, Peter Kaudewitz, Florian Klämpfl, Andreas Görtler |
| Fringe 2005, The 5th International Workshop on Automatic Processing of Fringe Patterns, 372-379 (2005) , Wolfgang Osten (Ed.), Springer, Berlin, Heidelberg, New York |
We report about the present state of our research project “UV Laser Therapy”: Its objective is the precise sensor controlled treatment of skin lesions such as dermatitis and psoriasis, using high power (UV-)excimer laser radiation. We present an optical 3D sensor that measures the lesion areas. The acquired 2D and 3D information is used to control the laser scanner for the reliable exposure of the lesion areas. The medical and commercial requirements for the sensor and the algorithms are high reliability, accurate and fast identification of the lesions and – last not least – low cost. These requirements can be satisfied by the sensor that is based on "Photometric Stereo" |
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Wolfsgruber_FRINGE2005.pdf
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| [182] | White-light interferometry with higher accuracy and more speed |
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Claus Richter, Bernhard Wiesner, Reinhard Groß, Gerd Häusler |
| Fringe 2005, The 5th International Workshop on Automatic Processing of Fringe Patterns, 605-612 (2005) , Wolfgang Osten (Ed.), Springer, Berlin, Heidelberg, New York |
White-light interferometry is a well established optical sensor principle for shape measurements. It provides high accuracy on a great variety of surface materials. However, to accomplish future industrial tasks several problems have to be solved.
One major task is to increase the scanning velocity. We will introduce a system based on a standard white-light interferometer which can achieve scanning speeds up to 100 µm/sec with a standard frame rate of 25 Hz. With an add-on to the hardware we achieve up to 10 times higher modulation in the signal, compared to the standard setup. To cope with the sub-sampled signals, we introduce new evaluation methods.
Another major task concerns the white-light interferometry on rough surfaces. Here the physically limited measuring uncertainty is determined by the random phase of the individual speckle interferograms. As a consequence, the standard deviation of the measured shape data is given by the roughness of the given surface. The statistical error in each measuring point depends on the brightness of the corresponding speckle. If the brightness is below the noise threshold of the camera, the measurement fails completely and an outlier occurs. We present a new method to reduce the measuring uncertainty and the number of outliers. In our method, we generate two or more statistically independent speckle patterns and evaluate these speckle patterns by assigning more weight to brighter speckles.
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Fringe05_richter_wiesner.pdf
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| [181] | Full-Field Shape Measurement of Specular Surfaces |
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Jürgen Kaminski, Svenja Lowitzsch, Markus C. Knauer, Gerd Häusler |
| Fringe 2005, The 5th International Workshop on Automatic Processing of Fringe Patterns, 372-379 (2005) , Wolfgang Osten (Ed.), Springer, Berlin, Heidelberg, New York |
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JNK_Fringe05_shapeofspecularsurfaces.pdf
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| [180] | Optical 3d-metrology for medical applications |
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Michaela Benz, J. Hartmann, Tobias Maier, Emeka Nkenke, Klaus Veit, A. Stellzig-Eisenhauer, F. W. Neukam, Gerd Häusler |
| Biomedizinische Technik. Proceedings of the jointly held Congresses ICMP 2005 and BMT 2005, 48-49 (2005) , U. Boenick, A. Bolz, W. Kalender, E.G. Hahn, A.M. Schulte (Ed.), Fachverlag Schiele und Schön, Berlin |
We present medical applications of optical 3d-metrology. One application is a quantitative evaluation of the operation result by a comparison of the pre- and postoperative surface and the localisation of facial asymmetries. Another objective is to support the surgeon intraoperatively by a nominal actual comparison. A further application is the manufacturing of dental prostheses. The 3d-data is acquired with our “phase-measuring triangulation sensor” that measures a complete 3d-view in 270 ms. We present methods for the computation of a symmetry plane of the face even in the presence of asymmetrical parts and for a quantitative comparison of different surfaces (e. g., pre-/postoperative). We further discuss the potentials of our methods to reconstruct facial asymmetries and to quantify facial surface changes. |
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MB_TM_BioMedTechnik2005.pdf
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| [0] | A new method to reduce the measuring uncertainty and the number of outliers in white-light interferometry |
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Bernhard Wiesner, Gerd Häusler |
| DGaO Proceedings, 106, A5 (2005) |
In white-light interferometry on rough surfaces (“Coherence Radar”) the physically-limited measuring uncertainty is determined by the arbitrary phase of the individual speckle interferograms. As a consequence, the standard deviation of the measured shape data is given by the roughness of the given surface. The statistical error in each measuring point depends on the brightness of the corresponding speckle; a dark speckle yields a more uncertain measurement than a bright one. If the brightness is below the noise threshold of the camera, the measurement fails completely and an outlier occurs.
We present a new method to reduce the measuring uncertainty and the number of outliers. In our method, we generate two or more statistically independent speckle patterns and evaluate these speckle patterns by assigning brighter speckles more weight. |
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| [179] | Informationsoptimierte Merkmale zur Grobregistrierung von Freiform-Flächen |
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Nikolaus Schön, Michaela Benz, Tobias Maier, Emeka Nkenke, F.W. Neukam, Gerd Häusler |
| Proceedings Bildverarbeitung für die Medizin 04, 116, 468-472 (2004) , Thomas Tolxdorff, Jürgen Braun, Heinz Handels, Alexander Horsch, Hans-Peter Meinzer (Ed.), CEUR-WS.org |
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KS_bmv04.pdf
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| [178] | Automatic Coarse Registration of 3D Surface Data in Oral and Maxillofacial Surgery |
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Tobias Maier, Michaela Benz, Nikolaus Schön, Emeka Nkenke, Friedrich Wilhelm Neukam, Gerd Häusler |
| Perspective in Image-Guided Surgery - Proceedings of the Scientific Workshop on Medical Robotics.., 51-58 (2004) , Buzug, Leuth (Ed.), World Scientific, Singapore |
Our aim is to support the surgeon during the adjustment of a displaced eye ball after a fracture of the zygomatic bone. Therefore, the facial surface is repeatedly measured intraoperatively by an optical range sensor. These data have to be registered with preoperatively modeled target data in order to perform a reproducible nominal/actual data comparison based on well defined criteria. Since the spatial orientation and position of the sensor relatively to the patient’s face can not be presumed, the registration process via the ICP-Algorithm requires a prior coarse registration. This paper presents a problem-oriented method for the fast automatic coarse registration of facial surfaces. The method exploits some characteristics of the Gaussian image that are invariant against the facial form changes caused by the surgical operation. |
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TobiasMaier_MRNV04_Paper.pdf
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| [175] | Quantitative Comparison of Facial Soft Tissue Surfaces |
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Michaela Benz, Manuel Kramer, Tobias Maier, Emeka Nkenke, Friedrich W. Neukam, Gerd Häusler |
| 3. Jahrestagung der Deutschen Gesellschaft für Computer- und Roboterassistierte Chirurgie e.V., http://www.curac.org/curac04/prog_curac.htm (2004) , CIII-21 |
This contribution presents an improvement in computer aided oral and maxillofacial surgery. We present a new quantitative method to compare free-form surfaces in 3D-space, especially facial soft tissue surfaces obtained by optical 3D-measurements. This is firstly needed to evaluate the surgery result and monitor its long-term stability, secondly for an intraoperative actual-nominal comparison. |
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MB_curac_2004.pdf
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| [174] | Vermessung spiegelnder Oberflächen - eine Aufgabe der optischen 3D-Sensorik |
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Markus C. Knauer, Klaus Veit |
| Photonik, 4, 62-64 (2004) |
Bei der Vermessung spiegelnder Freiformflächen, beispielsweise Präzisionsoptiken oder Brillengläser mit individuellen Asphären, kann die Phasenmessende Deflektometrie (PMD) eine Seite des Glases unabhängig von der anderen beurteilen. Um die lokale Neigung der Oberfläche zu ermitteln, projiziert eine Beleuchtungseinheit Streifenmuster mit sinusförmigen Intensitätsverteilungen auf eine Mattscheibe. Die gespiegelten Muster auf der Oberfläche des Messobjekts werden dann von einer Kamera aufgenommen und aus der Verzerrung der Muster kann direkt die lokale Neigung gemessen und daraus die lokale Oberflächenkrümmung berechnet werden. Darin liegt der entscheidende Vorteil gegenüber höhenmessenden Verfahren, deren Messdaten zweimal abgeleitet werden müssen, wodurch das hochfrequente Rauschen steigt. |
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MCK_Photonik_PMD_2004.pdf
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| [170] | Richtungscodierte Deflektometrie |
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Rainer Seßner, Gerd Häusler |
| DGaO-Proceedings, A16 (2004) |
Zur Vermessung spiegelnder Freiformflächen werden Verfahren benötigt, die eine eindeutige, schnelle Vermessung und Auswertung ermöglichen. Ein solches Verfahren ist die "Phasenmessende Deflektometrie (PMD)", bei der die Oberflächenneigung über die Verbiegung von reflektierten Sinus-Streifenmustern bestimmt wird. Bei einer nicht-telezentrischen Anordnung ist die gemessene Neigung abhängig von der Höhe des Messpunktes. Diese Höhenabhängigkeit muss durch Zusatzinformation herauskalibriert werden. Hier soll nun eine neue -telezentrische- Implementation von PMD vorgestellt werden, bei der durch direkte Codierung der Beleuchtungsrichtung die Oberflächennormale unabhängig von der Höhe im Messraum bestimmt wird. Mit dieser "Richtungscodierten (phasenmessenden) Deflektometrie" (RCD) ist nun eine konzeptuell einfache und genaue Erfassung der Oberflächennormale möglich. |
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| [167] | Absolute Phasenmessende Deflektometrie |
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Markus C. Knauer, Jürgen Kaminski, Gerd Häusler |
| DGaO-Proceedings, A15 (2004) |
Die "Phasenmessende Deflektometrie" (PMD) ist ein auf der Streifenprojektion basierendes Verfahren zur Vermessung spiegelnder Oberflächen. Die primäre Messgröße ist die lokale Neigung. Im Vortrag soll eine neue Methode vorgestellt werden, mit der zusätzlich zur Oberflächennormale n(x,y) die Höhe z(x,y) des Objekts bestimmt werden kann. Bisher war die Höhe nicht direkt messbar, sondern, im Gegenteil, zur exakten Neigungsberechnung unbedingt mit anzugeben. Mit der absoluten PMD können nun spiegelnde Freiformflächen beliebig im Messraum platziert und vermessen werden. |
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MCK_absolute_PMD_DGaO04.pdf
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| [166] | Phase Measuring Deflectometry: a new approach to measure specular free-form surfaces |
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Markus C. Knauer, Jürgen Kaminski, Gerd Häusler |
| Optical Metrology in Production Engineering, 5457, 366-376 (2004) , Wolfgang Osten, Mitsuo Takeda (Ed.), Proc. SPIE, Strasbourg, France |
We present a new method to measure specular free-form surfaces within seconds. We call the measuring principle `Phase Measuring Deflectometry' (PMD). With a stereo based enhancement of PMD we are able to measure both the height and the slope of the surface. The basic principle is to project sinusoidal fringe patterns onto a screen located remotely from the surface under test and to observe the fringe patterns reflected via the surface. Any slope variations of the surface lead to distortions of the patterns. Using well-known phase-shift algorithms, we can precisely measure these distortions and thus calculate the surface normal in each pixel. We will deduce the method's diffraction-theoretical limits and explain how to reach them. A major challenge is the necessary calibration. We solved this task by combining various photogrammetric methods. We reach a repeatability of the local slope down to a few arc seconds and an absolute accuracy of a few arc minutes. One important field of application is the measurement of the local curvature of progressive eyeglass lenses. We will present experimental results and compare these results with the theoretical limits.
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MCK_PMD_photonics04.pdf
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| [0] | Fast Automatic Registration of Varying 3D Surface Data in Oral and Maxillofacial Surgery |
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Tobias Maier, Michaela Benz, Nikolaus Schön, Emeka Nkenke, F.W. Neukam, Gerd Häusler |
| Proceedings of the 18th International Congress on Computer Assisted Radiology and Surgery, 1385 (2004) , H. Lemke, M. Vannier, K. Inamura, A. Farman, K. Doi (Ed.), Elsevier Science |
The authors have developed a support system for Oral and Maxillofacial Surgery. The surgeon can intraoperatively acquire updated optical 3D surface data of the patient’s face and compare them with preoperatively computed nominal data. For comparison the data have to be registered. This process is two-tiered: i) coarse and ii) fine registration (ICP-Algorithm). This contribution covers the first step and is an enhancement of an existing method of the authors. |
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TM_ICS1268_CARS04.pdf
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| [160] | Information theoretical optimization for optical range sensors |
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Christoph Wagner, Gerd Häusler |
| Applied Optics 42, 27, 5418-5426 (2003) |
Most of the known optical range sensors require a big amount of 2D raw data from which the 3D data is decoded, associated with considerable “cost”. The cost arises from expensive hardware as well as from the time necessary to acquire the images. We will address the question of how one can acquire a maximum shape information with a minimum amount of image raw data, in terms of information theory. It is shown that one can greatly reduce the amount of raw data needed by proper optical redundancy reduction. Through these considerations, a 3D sensor is introduced, needing only a single color (RGB) raw image and still delivering data with only about 2 µm longitudinal measurement uncertainty.
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CW_Information_AO_2003.pdf
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| [159] | How 3D sensors and rapid surfacing play together |
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Peter Klinger, Stefan Karbacher, Xavier Laboureux, Gerd Häusler |
| Proceedings book, the 8th International rendez-vous for 3D digitisation and modelling professionals (2003) , Paris |
In contrast to mechanical touch probes, optical 3D-sensors are not robust against features of the surface under test: the microtopology, the reflectivity and the slope of the surface may afflict the accuracy and the reliability of the measured data. Very high quality of 3D 360 degree views can only be achieved by a proper selection of the sensor type, by a proper measuring strategy, and by a posteriori “repair” via the surfacing process. We will discuss this “cooperation” between our 3D-sensors and our surfacing program SLIM3D. |
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PK_Paris_Processing_2003.pdf
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| [158] | Optical 3D Sensors for Real Applications – Potentials and Limits |
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Peter Klinger, Klaus Veit, Gerd Häusler, Stefan Karbacher, Xavier Laboureux |
| Proceedings book, the 8th International rendez-vous for 3D digitisation and modelling professionals (2003) , Paris |
Optical 3D-sensors measure local distances or the shape of surfaces, from the nanometer regime to the meter regime. Surprisingly, only three different physical mechanisms of signal formation are necessary to cover this range. These mechanisms determine different limits of the ultimate measuring uncertainty. We will discuss those limits of optical 3D-sensors and give rules to select the proper sensors for different applications. |
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PK_Paris_Sensors_2003.pdf
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| [155] | Automatische Grobregistrierung intraoperativ akquirierter 3D-Daten von Gesichtsoberflächen anhand ihrer Gauß'schen Abbilder |
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Tobias Maier, Michaela Benz, Gerd Häusler, Emeka Nkenke, F.W. Neukam, F. Vogt |
| Proceedings Bildverarbeitung für die Medizin '03 in Erlangen, 11-15 (2003) , Wittenberg et al. (Ed.), Springer |
Zur Unterstützung des Chirurgen bei der Korrektur von Augenfehlstellungen, wird intraoperativ durch Messungen mit einem optischen 3D-Sensor die Gesichtsoberfläche mehrmals im Laufe der Operation gemessen. Diese Daten müssen mit präoperativ modellierten Solldaten registriert werden, um einen objektiven Soll-Ist-Vergleich zu ermöglichen. Da die Orientierung des Sensors zum Patienten nicht als bekannt vorausgesetzt werden kann, ist eine Grobregistrierung vor der Feinregistrierung (ICP-Algorithmus) erforderlich. Es wird eine problemorientierte Methode zur schnellen automatischen Grobregistrierung von Gesichtsoberflächen vorgestellt. Die Methode nutzt Merkmale im Gauß'schen Abbild, welche invariant gegenüber der Gesichtsformveränderung durch den chirurgischen Eingriff sind. |
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TM_AutomGrob_2003.pdf
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| [156] | Three dimensional acquisition of colored objects |
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Nikolaus Schön, Peter Gall, Gerd Häusler |
| 8. Workshop Farbbildverarbeitung, ISSN 1432-3346, 63-70 (2002) , ZBS e. V., Ilmenau |
In this paper we present a system for the acquisition of color and shape of free form surfaces.
We place the emphasis on the methods for the acquisition and reconstruction of surface color. We discuss algorithms to eliminate illumination effects such as shading and specular highlights. We will further describe a procedure to merge the color information of multiple range images, utilising redundancy in overlapping regions, thus enhancing the appearance of the object. |
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KS_3DAcquisition_ColoredObjs_2002.pdf
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| [152] | The Symmetry of Faces |
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Michaela Benz, Xavier Laboureux, Tobias Maier, E. Nkenke, Stefan Seeger, F.W. Neukam, Gerd Häusler |
| Proc. of Vision, Modeling and Visualization, 20.-22. November 2002 Erlangen, 43-50 (2002) , G. Greiner, H. Niemann, T. Ertl, B. Girod, H.-P. Seidel (Ed.), Akademische Verlagsgesellschaft Aka GmbH, Berlin |
In this paper we present an application of optical metrology and image processing to oral and maxillofacial surgery. Our goal is to support the surgeon intraoperatively during the repair of a displacement of the globe of the eye. To date, the surgeon has to evaluate his operation result solely by visual judgement. Our idea is to provide the surgeon intraoperatively with a comparison of the actual 3D position of the globe of the eye and its nominal position. The nominal position is computed based on symmetry considerations. Therefore, we have developed a method to compute the symmetry plane of faces in the presence of considerable asymmetry. We tested this method on healthy faces and on faces with a defined asymmetric region created by injection of saline solution. |
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Benz_SymmetryofFaces_Aug2002.pdf
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| [151] | On-Line Ablation Measurement for Laser Material Processing |
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Peter Klinger, Gerd Häusler |
| 7th International Symposium on Laser Metrology, 9.-13. Sept. 2002, 4900, 195-201 (2002) , Proc. SPIE, Novosibirsk, Russia |
In Laser Material Processing, surfaces have to be measured at low apertures within the rough environment generated by the production process. As it is hardly possible to measure the material wear through the plasma at the working zone (at temperatures above 3000 K), common sensors would have a quite poor performance. The ablation sensor presented in this paper solves that problem by utilising just the plasma spot emitting a signal from which we evaluate the distance between sensor and work piece. The specific features of this sensor are: the measurement is not distorted by coherent noise and is insensitive against the (strongly varying) spot size and shape. Hence, the sensor displays extreme accuracy, even with low aperture and in presence of strong turbulence. The achievable measurement on-line uncertainty within the ablation process is ó = 3µm using a CO2-Laser. - A demand for even finer structures in laser ablation leads to a change from the Laser caving process (using a CO2-laser) to an ablation by sublimation (using a Nd:YAG laser). The intention is to decrease the thickness of each
ablated layer, and thus, generating finer structures. In order To keep the ablation rates at an economically interesting value,
the speed between laser and work piece surface has to be Increased. This new ablation process tightens the requirements for the sensor performance, even more. In the paper we will explain the basic ideas of the sensor as well as the technology of implementation and a couple of successful applications. |
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PK_OnLineAblationSensor.pdf
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| [146] | Corrupting coherence - ubquitous in the metrologists daily life |
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Gerd Häusler |
| Proc. 3rd Topical Meeting on Optoelectronic Distance Measurement and Applications (ODIMAP III), 282-287 (2001) , Prof. S. Donati (Ed.), Pavia, Italy |
The opticist usually classifies optical systems into the categories "coherent" and "incoherent". Commonly, systems are called coherent, if a laser is used (right), and incoherent if other sources come into play (wrong). Most opticists are not aware that parasitc spatial coherence is ubiquitous, even if it is unobvious, and the incoherent approach may lead to considerable quantitative measuring errors of illumination or reflectivity, 3d shape, size or distance. This report will discuss simple rules to estimate the occuring errors and how to reduce spatial coherence (in some lucky applications even to zero), and applications for the design of 3D-sensors. |
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OdimapPaper.PDF
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| [145] | A Sub-Atomic Subdivision Approach |
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Stefan Seeger, K. Hormann, Gerd Häusler, G. Greiner |
| Vision, Modeling and Visualization 2001, 77-85 (2001) , B. Girod, H. Niemann, H.-P. Seidel (Ed.), Akademische Verlagsgesellschaft, Berlin |
One of the main objectives of scientific work is the analysis of complex phenomena in order to reveal the underlying structures and to explain them by means of elementary rules which are easily understood.
In this paper we study how the well-known process of triangle mesh subdivision can be expressed in terms of the simplest mesh modification, namely the vertex split. Although this basic operation is capable of reproducing all common subdivision schemes if applied in the correct manner, we focus on Butterfly subdivision only for the purpose of perspicuity.
Our observations lead to an obvious representation of subdivision meshes as selectively refined progressive meshes, making them most applicable to view-dependent level-of-detail rendering. |
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vmv2001.pdf
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| [144] | Localization and registration of three-dimensional objects in space - where are the limits ? |
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Xavier Laboureux, Gerd Häusler |
| Applied Optics, 40, No.29, 5206-5216 (2001) , IEEE 2001 (Ed.) |
We discuss the accuracy limits for the localization of surfaces in three-dimensional (3-D) space. Such localization is necessary for the registration of different views of an object, taken by 3-D sensors from several directions. A quantitative analysis shows that the lateral localizations accuracy of a small surface area is proportional to the local curvature of the surface. This confirms the inituitive conjecture that our visual system performs localization of 3-D objects via sharp features. The longitudinal localization accuracy depends only on the noise of the data and is usually much better than the lateral localization accuracy, suggesting that surfaces are to be registered only along the longitudinal directions. |
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XL_limits_2001.pdf
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| [141] | In Process 3D-Sensing for Laser Material Processing |
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Peter Klinger, B. Spellenberg, Jürgen M. Herrmann, Gerd Häusler |
| Proceedings of Third International Conference on 3-D Digital Imaging and Modeling, 38- 41 (2001) , IEEE 2001 (Ed.), Quebec, Canada |
In this paper we present a new sensor that can measure the material wear in laser material processing online. To meet the demands of industrial production optical rough surfaces have to be measured at low apertures under the rough enviroment generated by the production process. This limits common sensors to a well defined achievable resolution. It is hardly possible to measure the material wear through the plasma occurring in the working zone at temperatures above 3000K. We utilise this plasma spot as a signal from which we derive the distance between sensor and work piece. The specific features are: this sensor is insensitive against the spot size and shape. A point of measurement can be obtained every millisecond.
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PK_3DSensing_2001.pdf
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| [140] | How much 3D-Information can we acquire? |
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Gerd Häusler |
| Proceedings of Third International Conference on 3-D Imaging and Modeling, 281 (2001) , IEEE 2001 (Ed.), Quebec, Canada |
Most of the problems of industrial inspection, reverse engineering and virtual reality, require data about the geometrical shape of objects in 3-D space. Such 3-D data offer advantages over 2-D data: shape data invariant against alteration of the illumination, soiling and object rotation... Unfortunately, this data is much more difficult to acquire than video data about the 2-D local reflectivity of objects. We will discuss the physics of 3-D sensing and will address the following subjects:
- coherent and incoherent illumination
- interaction of light with matter, at rough surfaces and at smooth surfaces
- the consequences of Heisenberg´s uncertainty relation. |
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GH_Limits_2001.pdf
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| [139] | Refining Triangle Meshes by Non-Linear Subdivision |
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Stefan Karbacher, Stefan Seeger, Gerd Häusler |
| Proceedings of Third International Conference on 3-D Digital Imaging and Modeling 2001, 270-277 (2001) , IEEE, Quebec, Canada |
Subdivision schemes are commonly used to obtain dense or smooth data representations from sparse discrete data. E. g., B-splines are smooth curves or surfaces that can be constructed by infinite subdivision of a polyline or polygon mesh of control points. New vertices are computed by linear combinations of the initial control points. We present a new non-linear subdivision scheme for the refinement of triangle meshes that generates smooth surfaces with minimum curvature variations. It is based on a combination of edge splitting operations and interpolation by blending circular arcs. In contrast to most conventional methods, the final mesh density may be locally adapted to the structure of the mesh. As an application we demonstrate how this subdivision scheme can be used to reconstruct missing range data
of incompletely digitized 3-D objects. |
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SBK_RefngTriangMeshs_2001.pdf
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| [138] | Processing Range Data for Reverse Engineering and Virtual Reality |
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Stefan Karbacher, Xavier Laboureux, Nikolaus Schön, Gerd Häusler |
| Proceedings of Third International Conference on 3-D Digital Imaging and Modeling 2001, 314-321 (2001) , IEEE, Quebec, Canada |
Optical 3-D sensors are used as tools for reverse engineering and virtual reality to digitize the surface of real threedimensional objects. We discuss an almost fully automatic method to generate a surface description based on a mesh of curved or flat triangles. The method includes mesh reduction, smoothing, and reconstruction of missing data. The generated meshes feature minimum curvature variations and are therefore especially suited for visualization and rapid prototyping. |
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SBK_RangeDataProcs_2001.pdf
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| [163] | Metrical Calibration of a Phase Measuring Triangulation Sensor |
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Klaus Veit, Gerd Häusler |
| Proceedings of "Vision, Modelling and Visualization 2000", 33-38 (2000) , Saarbrücken |
Metrical calibration is very critical for the accuracy of a 3d sensor. Measuring uncertainty of about 1:3000 of the z-range requires a calibration accuracy of about 1:104. Several model-based approaches for this problem exist. In this article the calibration task for a phase measuring triangulation sensor is described. After a short description of the geometrical distortions that are compensated for a non-model based algorithm for the metrical calibration is presented. The main idea is the splitting into a longitudinal z-calibration and a lateral x-y-calibration. For z-calibration a linear interpolation is used, whereas the x-ycalibration is performed by a polynomial approach.
The polynomial coefficients are obtained by a least squares method. The algorithm is tested using a laboratory 3d sensor.
The results are discussed and compared with the accuracy of other calibration algorithms. |
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KV_Metrical_2000.pdf
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| [147] | Optical Coherence Tomography by „Spectral Radar“: Improvement of Signal-to-Noise Ratio |
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Peter Andretzky, Markus C. Knauer, F. Kiesewetter, Gerd Häusler |
| SPIE, 3915, 55-59 (2000) |
"Spectral radar" combines a white light interferometer with a spectrometer. It is an optical sensor for the acquisition of skin
morphology based on OCT techniques. The scattering amplitude along one vertical axis from the surface into the bulk can be
measured within one exposure. We will discuss some essentials of signal formation and a new method of signal evaluation that significantly reduces artifacts from some source imperfections. We will further demonstrate new measurements. |
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PFA_OptCoherTomography_2000.pdf
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| [136] | Fusion of discrete Models |
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Stefan Karbacher |
| Principles of 3D Image Analysis and Synthesis, 175-180 (2000) , In B. Girod, G. Greiner und H. Niemann (Ed.), Kuwer Academic Publishers, London |
This section provides a survey on methods to reconstruct the topology of a surface from multiple geometric data sets like range images or point clouds. The topology of a sampled object is defined by the neighborhood structure of the data points (see
Section 4.1.2). For a single range image this is simply given by the order of the CCD pixel matrix. Topology reconstruction is trivial in this case. Using multiple data sets, the points of the different viewpoints must be merged and the topology has to be recomputed. |
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SBK_DiscModelFusion_2000.pdf
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| [135] | Discrete Modeling of Point Clouds |
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Stefan Karbacher |
| Principles of 3D Image Analysis and Synthesis, 166-180 (2000) , In B. Girod, G. Greiner und H. Niemann (Ed.), Kluwer Academic Publishers, London |
After scanning threedimensional objects (see Section 4.4) or triangulating CAD surfaces one usually gets point clouds or triangular meshes as a result. Frequently it is necessary to process this data. Calibration and registration errors, for example, appear after merging multiple range images from different views. These data are not structured and therefore it is not possible to use conventionalmodeling or signal processing
methods like tensor product surfaces or linear filters. |
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SBK_PointCloudModeling_2000.pdf
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| [134] | Feature Extraction and Registration |
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Stefan Seeger, Xavier Laboureux |
| Principles of 3D Image Analysis and Synthesis, 153-166 (2000) , B. Girod, G. Greiner und H. Niemann (Ed.), Kluwer Academic Publishers, Boston - Dordrecht - London |
The purpose of this paper is to present a survey of rigid registration (also called matching)methods applicable to surface descriptions. As features are often used for the registration task, standard feature extraction approaches are described in addition. In order to give the reader a framework for his resent registration problem, this report divides the matching task into three major parts (feature extraction, similarity metrics and search strategies). In each of them the reader has to decide between several possibilities, whose relations are in particularly pointed out. |
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SNS_FeatExtrac-Reg_2000.pdf
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Stefan Karbacher, S. Campagna |
| Principles of 3D Image Analysis and Synthesis, 142-152 (2000) , B. Girod, G. Greiner und H. Niemann (Ed.), Kluwer Academic Publishers, Boston - Dordrecht - London |
Triangle meshes are the simplest type of polygon meshes. Since polygon meshes can be converted into triangle meshes simply by triangulating all polygons with n > 3, this introduction focuses on triangle meshes.
At present triangles are the only surface primitive that can be rendered directly by graphics hardware. Hence, all surface descriptions must be approximated by triangle meshes for interactive visualization. Triangle meshes are very flexible. In contrast to tensor product surfaces, for example, they can describe surfaces of arbitrary topology, even with nonmanifold elements. Furthermore, the density of vertices can be locally adapted to the surface curvature. Since triangles are a very simple kind of geometric primitive, algorithms for triangle meshes are usually efficient and robust. |
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SBK_PolygMeshes_2000.pdf
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| [132] | Illumination estimation |
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Nikolaus Schön, P. Eisert |
| Principles of 3D Image Analysis and Synthesis, 153-166 (2000) , B. Girod, G. Greiner, H. Niemann (Ed.), Kluwer Academic Publishers, London |
When analyzing multiple views or image sequences for object tracking or recovering geometrical structure, one has to deal with the dependence of 2D images on the illumination conditions of the observed scene. Object tracking relies on the fact that the object looks similar in successive views. However, a change of its position relative to the illuminant or varying illuminants cause effects like glossy regions appearing on different parts of the surface and a change in the observed brightness and color of other surface elements. This is also problematic for motion estimation, because intensity variations caused by a change of illumination conditions have to be distinguished from those variations caused by object movement. There are other applications that require the compensation of illumination effects. In Computer Graphics, visualization techniques require the essential colors of a surface, that depend only on the reflection characteristic of the object, not on the illumination conditions during their measurement.
Another example is the search of 2D images in a database that contains only datasets acquired under definite illumination conditions. Illumination effects have to be removed from a new image to make it comparable to the ones in the database. |
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NS_IluminEst_2000.pdf
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| [130] | Digitizing 3D objects for reverse engineering and virtual reality |
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Stefan Karbacher, Nikolaus Schön, Harald Schönfeld, Gerd Häusler |
| Principles of 3D Image Analysis and Synthesis, 336-347 (2000) , B. Girod, G. Greiner und H. Niemann (Ed.), Kluwer Academic Publishers, London |
Optical 3D sensors are used as tools for reverse engineering and virtual reality to digitize the surface of real 3D objects. Common interactive surface reconstruction is used to convert the sensor point cloud data into a parametric CAD description (e.g. NURBS). We discuss an almost fully automatic method to generate a surface description based on a mesh of curved or flat triangles. |
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SBK_Digitizing3DObj_2000.pdf
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| [129] | A Non-linear Subdivision Scheme for Triangle Meshes |
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Stefan Karbacher, Stefan Seeger, Gerd Häusler |
| Proc. of Vision, Modeling and Visualization 2000, 163-170 (2000) , Girod, G. Greiner, H. Niemann, H.-P. Seidel (Ed.), Akademische Verlagsgesellschaft Aka GmbH, Berlin |
Subdivision schemes are commonly used to obtain dense or smooth data representations from sparse discrete data. E. g., B-splines are smooth curves or surfaces that can be constructed by infinite subdivision of a polyline or polygon mesh of control points. New vertices are computed by linear combinations of the initial control points.
We present a new non-linear subdivision scheme for the refinement of triangle meshes that generates smooth surfaces with minimum curvature variations. It is based on a combination of edge splitting operations and interpolation by blending circular arcs. In contrast to most conventional methods the final mesh density may be locally adapted to the structure of the mesh. As an application we demonstrate how this subdivision
scheme can be used to reconstruct missing range data of incompletely digitized 3-D objects. |
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SBK_NonLinSubdiv_TriangMeshes_2000.pdf
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| [128] | A Robust Multiresolution Registration Approach |
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Stefan Seeger, Gerd Häusler |
| Proc. of Vision, Modeling and Visualization `99, 75-82 (1999) , B. Girod, H. Niemann, H.-P.Seidel (Ed.), Infix Verlag, Sankt Augustin |
The task of registering several range images taken from different viewpoints into a single coordinate system is usually divided into two steps: first, finding a rough estimate of the searched transformation on the base of reduced parts of the data sets, and second, finding the precise transformation with another method on the base of the complete information given by the data sets. Using different approaches for these registration steps has no fundamental but only practical reasons: for the fine tuning step it exists an easily implementable algorithm whose efficiency and precision has been proven in many experiments, but which is not applicable for finding an initial rough estimate of the searched transformation. We present a multiresolution approach to the registration problem that has the potential to combine these two registration steps and is based on hierarchical Hough methods and local frames defined in each surface point. |
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SNS_Robust_MultRes_App_1999.pdf
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| [121] | Fast 3d - Camera for Industrial and Medical Applications |
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Gunther Bohn, L. Cloutot, Hans Peter Habermeier, Ralf Lampalzer, Alexander Schröter, Nikolaus Schön, Klaus Veit, Gerd Häusler |
| Proc. of ODIMAP II, 214-219, 2nd Topical Meeting on Optoelectronic Distance/Displacement (1999) , University of Pavia, Italy |
We report a new concept for a Phase Measuring Triangulation sensor which has the potential to acquire 3d-data in video real time or even faster. The measuring uncertainty is about 1/2000 of the measuring range, the latter scalable from 5mm up to 1m. Because of the short measuring time the sensor has the capability of in vivo measurements of human skin topology. We report about results of a full 360 degree three-dimensional acquisition of objects, including the color texture. We discuss results in industrial metrology (solder paste inspection). |
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GB_fast_3d_cam_1999.pdf
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| [120] | Three-Dimensional Sensors - Potentials and Limitations |
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Gerd Häusler |
| Handbook of Computer Vision and Applications, Vol. 1: Sensors and Imaging, 485-506 (1999) , B. Jähne, H. Haußecker und P. Geißler (Ed.), Academic Press, Boston |
We discuss the physics of 3-D sensing, and will address the following subjects:
- different type of illumination (coherent or incoherent, structured or unstructured)
-Interaction of light with matter (coherent or incoherent, at rough surfaces of at smooth surfaces)
- the consequences of Heisenberg´s uncertainty relation. |
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GH_3DSens_Pot&Lims_1999.pdf
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| [119] | Visualization and detection of small defects on car-bodies |
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Stefan Karbacher, Gerd Häusler, Jan Babst, Xavier Laboureux |
| Vision, Modeling and Visualization '99, 1-8 (1999) , B. Girod, H. Niemann, H.-P. Seidel (Ed.), Infix, Sankt Augustin |
Sheet metals of car bodies sometimes have small defects, e. g. dents or ripples with a depth of only a few microns. These defects usually are not vis-ible until varnish is applied. It would be conve-nient to detect them in advance in order to sim-plify repairing. We demonstrate how they can be visualized by using optical 3-d sensors and optimum signal processing. For a German car company we developed a fast algorithm that is based on this visualization method.
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SBK_VisDet_CarBds_1999.pdf
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| [117] | Reverse engineering using optical range sensors |
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Stefan Karbacher, Gerd Häusler, Harald Schönfeld |
| Handbook of Computer Vision and Applications: Systems and Applications, 3, 359-380 (1999) , B. Jähne, H. Haußecker, P. Geißler (Ed.), Academic Press Boston |
Optical 3-D sensors are used as tools for reverse engineering to digitize the surface of real 3-D objects (see Chapter 20). Common interactive surface reconstruction is used to convert the sensor point cloud data into a parametric CAD description (e. g., NURBS). We discuss an almost fully automatic method to generate a surface description based on a mesh of curved or flat triangles [...] |
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SBK_RevEng_RangeSens_1999.pdf
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| [125] | Aufbereitung von 3D-Sensordaten für Reverse Engineering mit Slim3D |
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Xavier Laboureux, Gerd Häusler, Stefan Karbacher, H. Schönfeld |
| Optische 3D-Formerfassung, 5.ABW-Workshop 20.-21. 1.1998 (1998) , H. Wolf (Ed.), Technische Akademie Esslingen, Ostfildern |
Slim3D ist ein Programmpaket zur Aufbereitung der Daten optischer 3D-Messsysteme für Reverse Engeneering, Virtual Reality or Rapid Prototyping [...] |
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XL_3DSens_mitSlim_1998.pdf
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| [116] | Modifications of the coherence radar for in vivo profilometry in dermatology |
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Peter Andretzky, Michael W. Lindner, J. Neumann, Gunther Bohn, Marc Schmidt, Gerd Häusler |
| Proc. of SPIE, 3567, 88-96 (1998) |
Important aims in dermatology are the measurement of pathological alterations of human skin and on the other hand the quantification of the influences caused by pharmaceutic and cosmetic products. We present modifications of the well established coherence radar that allow in vivo measurements of human skin in spite of involuntary body movements and bloodflow. The measuring field can be varied from 100 x 100 µm² to 5 x 5 mm². The measuring time is 5 to 15 s and the longitudinal measuring uncertainty is about 2 µm. A fiberoptical implementation allows the separation of the sensor head from the mechanical scan. The mobile and compact sensor head can now be freely positioned and adjusted to each part of the patients skin. Disturbances caused by unavoidable movement of the patient can be compensated by modified setups of the coherence radar. We show measurements of clinical and cosmetical relevance. |
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PFA_ModKORAD_prolfilometry_1998.pdf
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| [115] | Optical Coherence Tomography by „spectral radar“: dynamic range estimation and in vivo measurements |
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Peter Andretzky, Michael W. Lindner, Jürgen M. Herrmann, A. Schultz, M. Konzog, F. Kieswetter, Gerd Häusler |
| Proc. of SPIE, 3567, 78-87 (1998) |
The „Spectral Radar“ is an optical sensor for tomography, working in the Fourier domain, rather than in time domain.
The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. One important property of optical coherence tomography (OCT) sensors is the dynamic range. We will compare the dynamic range of the spectral radar with standard OCT.
The influence of the Fourier transformation on the dynamic range of the Spectral Radar will be discussed. The clinical
relevance of the in vivo measurements will be demonstrated. |
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PFA_OptCoherTomography_1998.pdf
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| [114] | A new approach for modeling and smoothing of scattered 3D data |
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Stefan Karbacher, Gerd Häusler |
| Three-Dimensional Image Capture and Applications, Proceedings of SPIE, 3313, 168-177 (1998) , Richard N. Ellson und Joseph H. Nurre (Ed.) |
In order to digitize the whole surface of a three-dimensional object by means of an optical range sensor, usually multiple range images are acquired from different viewpoints and merged into a single surface description. The simplest and most accurate way is to generate a polyhedral surface. The data are usually distorted by measuring errors like noise, aliasing, outliers, calibration and registration errors, etc., so that they have to be filtered. Calibration and registration errors first appear after merging of different views. As the merged data are no longer represented on a grid, conventional filters for digital signal processing are not applicable. We introduce a new approach for modeling and smoothing scattered data based on an approximation of a mesh of circular arcs. This new method enables interpolation of curved surfaces using solely the vertex position and the associated vertex normals of a polyhedral mesh. The new smoothing filter is specifically adapted to the requirements of geometric data, as it minimizes curvature variations. In contrast to linear filters, undesired surface undulations are avoided, which is an important pre-condition for NC milling and rendering. |
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SBK_Scatterd3D_data_1998.pdf
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| [113] | Reverse engineering using optical 3D sensors |
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| [111] | Roughness parameters and surface deformation measured by "Coherence Radar" |
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Peter Ettl, B. Schmidt, M. Schenk, Ildiko Laszlo, Gerd Häusler |
| International Conference on Applied Optical Metrology, June 8-11 (1998) , Balatonfüred, Hungary |
The "coherence radar" was introduced as a method to measure the topology of optically rough surfaces. The basic principle is white light interferometry in individual speckles. We will discuss the potentials and limitations of the coherence radar to measure the microtopology, the roughness parameters, and the out of plane deformation of smooth and rough object surfaces.
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balaton98.pdf
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| [112] | Reconstruction of Smoothed Polyhedral Surfaces from Multiple Range Images |
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Gerd Häusler, Stefan Karbacher |
| 3D Image Analysis and Synthesis '97, 191-198 (1997) , B. Girod, H. Niemann, H.-P. Seidel (Ed.), Infix Verlag, Sankt Augustin |
In order to digitize the whole surface of a three dimensional object by means of an optical range sensor, usually multiple range images are acquired from different viewpoints. We demonstrated how the range images can be accurately merged into a single triangular mesh with curvature dependent density by the use of local topological mesh operations. A new filter, that is specially adapted to the requirements of geometrical data, has been designed. This enables smoothing of measuring errors like noise, aliasing, outliers, and registration errors with minimum interference of real object features like edges. Curvature variations are minimized and surface undulations are avoided in order to produce high quality surfaces for rendering and NC filling.
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SBK_PolyhedralSurfs_Reconstr_1997.pdf
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| [108] | About the Scaling Behavior of Optical Range Sensors |
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Gerd Häusler |
| Proc. of the 3rd Int. Workshop on Automatic Processing of Fringe Patterns, 147-155 (1997) , Bremen, Germany, September 15-17 |
We will discuss shape measurement methods in terms of the scaling behavior of their performance, such as longitudinal measuring uncertainty, measuring range, stand-off, lateral field and lateral resolution. It turns out that there are (only) three classes of shape measurement methods that differ significantly in their scaling behavior, as well as in their wide scale applicability: triangulation, multi-lambda interferometry, and monochromatic (classical) interferometry. |
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GH_Scaling1997.pdf
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| [107] | New modifications on the coherence radar |
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Gerald Ammon, Peter Andretzky, S. Blossey, Gunther Bohn, Peter Ettl, Hans Peter Habermeier, Gerd Häusler, I. Laszlo, B. Schmidt |
| Proc. of the 3rd Int. Workshop on Automatic Processing of Fringe Patterns, September 15-17, 237-246 (1997) , Bremen, Germany |
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GA_KoradMod_1997.pdf
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| [106] | 3D Real Time Camera |
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Gerd Häusler, M.B. Hernanz, Ralf Lampalzer, H. Schönfeld |
| Proc. of the 3rd Int. Workshop on Automatic Processing of Fringe Patterns, 247-249 (1997) , Bremen, Germany, September 15-17 |
A novel sensor for fringe projection is introduced. The sensor allows the acquisition of the shape of objects within a measuring time of only a few video cycles. The measuring uncertainty of the sensor is low, because fringes of an exactly sinusoidal intensity distribution are projected and because the remaining coherence of the illumination is low.
The properties are achieved by the use of a projection principle based on a fast-switching ferroelectric liquid crystal display. Two spatial frequencies of the fringes can be used. Thus an extended measuring range is possible without a (time consuming) phase unwrapping. |
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GH_3DRTCamera_1997.pdf
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| [105] | KORAD - new modifications of white light interferometry for large object shape acquisition |
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Gerald Ammon, Peter Andretzky, S. Blossey, Gunther Bohn, Peter Ettl, Hans Peter Habermeier, B. Harand, Gerd Häusler |
| Proc. of the EOS Topical Meeting on Optoelectronics Distance Measurements and Applications (1997) , Nantes |
The ‘coherence radar’ is a 3D-sensor based on interferometry with a broad bandwidth light source. This sensor principle combines the advantages of absolut measurements with a low measurement uncertainty limited only by the surface roughness of the object under test.
We introduce new sensor modifications which enable us to measure large objects (>100mm x 100mm), to measure the difference between an object under test and a master object and to measure strongly curved polished surfaces (e.g. aspheric lenses). We demonstrate a modification which reduces the measurement time considerably.
We discuss new measurements for different applications as turbine blades, silicon, solar cells and circuit boards. |
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GA_KORAD_LObjMod_1997.pdf
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| [101] | New Range Sensors at the Physical Limit of Measuring Uncertainty |
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Gerd Häusler, S. Kreipl, Ralf Lampalzer, A. Schielzeth, B. Spellenberg |
| Proc. of the EOS Topical Meeting on Optoelectronics Distance Measurements and Applications (1997) , Nantes, July, 8-10 |
Coherent noise is the major source of the measuring uncertainty of triangulation at rough surfaces. This is well known for laser based systems. We will discuss coherent noise in phase measuring triangulation systems that work with white, large incandescent lamps. Surprisingly, the remaining small amount of coherence still limits the distance uncertainty of all triangulation sensors. We will demonstrate two new sensors that utilize this knowledge, and display extremely small distance uncertainty.
One sensor is completely incoherent and can be applied to on-line measurement during laser material processing, the other sensor is a “real time“ 3D-video camera. |
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GH_NewRangeSens_1997.pdf
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| [100] | Physikalische Grenzen der optischen Formerfassung mit Licht |
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Gerd Häusler, G. Leuchs |
| Physikalische Blätter 53, Nr. 5, 417-421 (1997) |
Für die industrielle Produktion und Qualitätssicherung ist die geometrische Gestalt von Werkstücken, kurz ihre "Form", fast immer von entscheidender Bedeutung. Optische, d.h. berührungslose und schnelle Formerfassung ist also gefragt. Dabei setzen aber sowohl die Wellenoptik als auch die Quantenoptik eine Reihe physikalischer Grenzen. Deren Kenntnis erlaubt uns, die Leistung verfügbarer Sensoren am physikalisch Möglichen zu messen. Die Erforschung dieser Grenzen hat in den letzten Jahren zu 3D-Sensoren mit völlig neuen Eigenschaften geführt. |
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GH_Grenzen_1997.pdf
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| [97] | 3D-imaging of human skin - optical in vivo Tomography and Topology by short coherence interferometry |
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M. Bail, A. Eigensee, Gerd Häusler, Jürgen M. Herrmann, Michael W. Lindner |
| SPIE 2981, 64-75 (1997) |
We discuss different modifications of white light interferometry, for the acquisition of human skin morphology. In a first experiment we display the diffusion of light within tissue, versus time. Light is focused onto the surface of the sample, penetrates the sample, is scattered and partly emerges from the surface again. For each point of the surface we can measure a certain run time profile of the emerging photons, via the speckle contrast. The local scattering behavior of the skin is encoded in the run time profile.
Further we present a sensor for the acquisition of cross-sectional images of volume scatterers, we call it "spectral radar". The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary, hence a short measurement time is possible. The depth uncertainty within a range of 1000µm is about 10µm. In first measurements we distinguished a melanoma maligna from healthy skin, in vitro and we measured the thickness of a fingernail in vivo.
We further demonstrate a third method, the “coherence radar“ for in vivo measurements of skin surface topology, with an accuracy of a few micrometers, and a field of 512x512 pixels. |
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MB_Skin_1997.pdf
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| [95] | A new method of short-coherence interferometry in human skin (in vivo) and in solid volume scatterer |
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A. Eigensee, Gerd Häusler, Jürgen M. Herrmann, Michael W. Lindner |
| Proc. of the European Biomedical Optics Week, Vienna, 7-10 September, 169-178 (1996) , SPIE 2925, Vienna |
We adapted a method, the „coherence radar“, that was originally developed for the precise measurement of surface topology, to measure bulk properties within strongly scattering media. The sensor is based on short-coherence-interferometry. It enables the two-dimensional observation of light propagation in
scattering media with a high temporal resolution (<100 fs). The measurements are carried out by observing photons that traveled from an entrance focus through the bulk of the sample, and back to the surface. The source of information is the speckle contrast. One important result is that during the propagation a sharp photon horizon evolves. This photon horizon can be used for the detection of inhomogeneities in the scattering properties. In solid samples we measured absorbing obstacles with a depth of 320 µm and a depth uncertainty of <5%. The measuring time is about 30 seconds. The observation of the photon horizon can also be realized in „life“ volume scatterers with moving scattering particles. First in vivo measurements of human skin have been successful. |
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AE_Skin_1996.pdf
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| [94] | Optical coherence tomography with the „Spectral Radar“.-.Fast optical analysis in volume scatterers |
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M. Bail, Gerd Häusler, Jürgen M. Herrmann, Michael W. Lindner, R. Ringler |
| Proc. of the European Biomedical Optics Week 7-10 September, 21, No. 14, 298-303 (1996) , SPIE 2925 (Ed.), Vienna, Austria |
We present a sensor for acquisition of cross-sectional images of volume scatterers (e.g. biological tissue), we call it "spectral radar". Medical and technical applications are possible. The sensor is a modified Michelson-interferometer, with a broad bandwidth light source. The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. Measurement results of stationary and non stationary scattering phantoms, human skin and of a fish eye in vitro are shown. |
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MB_OptCoher_Tomography_96.pdf
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| [88] | Observation of light propagation in volume scatterers with 1011-fold slow motion |
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Gerd Häusler, Hans Peter Habermeier, R. Kummer, Michael W. Lindner |
| Optics letters, 21, No. 14, 1087-1089 (1996) |
An optical method is introduced for observation of temporally and spatially resolved frames that show how light propagates in diffussely scattering material. The method permits videos with 100-fs resolution in time to be produced. The method utilizes short-coherence interferometry. The source of information is the speckle contrast. The temporal and spatial evolution of the mzltiple scattering process is demonstrated for several biological and industrial samples. A major objective of the method is to investigate the conditions for optimal coherence and optimal apertures to achieve hig resolution in the short-coherence interferometry. One important result is that during the propagation a sharp photon horizon evolves, which is useful for the morphological analysis of volume scatterers. |
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GH_Propagation_1995.pdf
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| [74] | Laser triangulation: Fundamental uncertainty in distance measurement |
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Rainer G. Dorsch, Gerd Häusler, Jürgen M. Herrmann |
| Applied Optics, 33, 7, 1306-1314 (1994) |
We discuss the uncertainty limit in distance sensing by laser triangulation. The uncertainty in distance mesasurement of laser triangulation sensors and other coherent sensors is limited by speckle noise. Speckle arise because of the coherent illumination in combination with rough surfaces. A minimum limit on the distance uncertainty is derived through speckle statistics. This uncertainty is a function of wavelength obervation aperture, and speckle contrast in the spot image. Surprisingly, it is the same distance uncertainty that we obtained from a single-photon experiment and from Heisenberg´s resolution and distance uncertainly is introduced. Design criteria for a sensor with minimun distance uncertainty are determined: small temportal coherence, small spatial coherence, a large observation aperture. |
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RDD_LaserTriang_1994.pdf
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| [70] | 3D-sensing of rough surfaces by 'coherence radar' |
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Thomas Dresel, Gerd Häusler, Holger Venzke |
| Applied Optics, 31 No. 7, 919-925 (1992) |
We introduce a three-dimensional sensor, designed primarily for rough objects, that supplies an acccuracy that is limited only by the roughness of the objects surface. This differs from convetional optical systems in which the depth accuracy is limited by the aperture. Consecuently, our sensor supplies high accuracy with a small aperture, i.e., we can probe narrow crevices and holes. The sensor is based on a Michelson interferometer, with the rough object surface serving as one mirror. The small coherence lenght of the light source is used. While scannign the object in depth, one can detect the local occurrence of interference within the speckles emerging from the object. We call this method coherence radar.
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TD_3DSensing_roughSuf_1992.pdf
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| [42] | Optical simulation of Huygens' principle |
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G. Bickel, Gerd Häusler |
| JOSA A 5, 843-848 (1988) |
The two-dimensional stationary-wave equation (Helmholtz equation) can be solved by a simple linear-optical filtering experiment for arbitraty source distributions. The experiment can be considerd as direct visualization of Huygens´s principle, i.e., each point of an initial wave front can be regarded as the sourde of an elementray wave. Many phenomena can be visualized: diffraction, interference (including Talbot effect, Bragg effect) with monochromatica and polychromatic light, birefringence, etc. Optical filtering can be applied to other linear differential equations with constant coefficients too, such as the Poisson equation an the diffusion equation. |
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GB_Huygens_1988.pdf
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- Research & Papers - Papers - |
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