5D hyperspectral imaging: fast and accurate measurement of surface shape and spectral characteristics using structured light

Measuring the shape (coordinates x, y, z ) and spectral characteristics (wavelength-dependent reflectance R (λi)) of macroscopic objects as a function of time (t) is of great interest in areas such as medical imaging, precision agriculture, or optical sorting. Here, we present an approach that allows to determine all these quantities with high resolution and accuracy, enabling measurement in five dimensions. We call this approach 5D hyperspectral imaging. We describe the design and implementation of a 5D sensor operating in the visible to near-infrared spectral range, which provides excellent spatial and spectral resolution, great depth accuracy, and high frame rates. The results of various experiments strongly indicate the great benefit of the new technology

GOBO projection for 3D measurements at highest frame rates: a performance analysis

Aperiodic sinusoidal patterns that are cast by a GOBO (GOes Before Optics) projector are a powerful tool for optically measuring the surface topography of moving or deforming objects with very high speed and accuracy. We optimised the first experimental setup that we were able to measure inflating car airbags at frame rates of more than 50 kHz while achieving a 3D point standard deviation of ~500 µm. Here, we theoretically investigate the method of GOBO projection of aperiodic sinusoidal fringes. In a simulation-based performance analysis, we examine the parameters that influence the accuracy of the measurement result and identify an optimal pattern design that yields the highest measurement accuracy. We compare the results with those that were obtained via GOBO projection of phase-shifted sinusoidal fringes. Finally, we experimentally verify the theoretical findings. We show that the proposed technique has several advantages over conventional fringe projection techniques, as the easy-to-build and cost-effective GOBO projector can provide a high radiant flux, allows high frame rates, and can be used over a wide spectral range

A-priori calibration of a structured light underwater 3D sensor

In this study, we introduce a new calibration method for underwater optical stereo scanners. It uses air calibration, additional underwater parameters, and extended camera modeling. The new methodology can be applied to both passive photogrammetric and structured light three-dimensional (3D) scanning systems. The novel camera model uses a variable principal distance depending on the radial distance to the principal point instead of two-dimensional distortion functions. This allows for an initial improvement of 3D reconstruction quality. In a second step, certain underwater-specific parameters—such as refraction indices, glass thickness, and view-port distances—are determined. Finally, a correction function for the entire measurement volume can be obtained from a few underwater measurements. Its application further improves the measurement accuracy. Measurement examples show the performance of the new calibration method in comparison to current underwater calibration strategies. A discussion of the possibilities and limits of the new calibration method and an outlook for future work complete this work

Verfahren und Vorrichtung zum berührungslosen Vermessen dreidimensionaler Oberflächenkonturen

Die Erfindung betrifft ein Verfahren zum berührungslosen Vermessen dreidimensionaler Oberflächenkonturen mittels einer eine Projektionsvorrichtung (1) und eine Kamera (2a) aufweisenden Messvorrichtung (100). Dabei wird für jeden einer Mehrzahl von Bildpunkten (22, 32, 42, 52) in einer Bildebene (6a) der Kamera (2a) eine Korrelation zwischen einer dem jeweiligen Bildpunkt zugeordneten Folge von aufgenommenen Helligkeitswerten (43) und einer Auswahl aus einer Vielzahl von in einem Speicher hinterlegten Referenzhelligkeitswertfolgen (42a-d) maximiert, wobei für jede von einer Vielzahl von Stützstellen (20a-d, 30a-d, 40a-d, 50a-d), die als Punkte im Messvolumen (18) relativ zur Messvorrichtung (100) definiert sind und die das Messvolumen (18) aufspannen, jeweils eine der Referenzhelligkeitswertfolgen (42a-d) zusammen mit drei Raumkoordinaten der jeweiligen Stützstelle hinterlegt ist, so dass jede der hinterlegten Referenzhelligkeitswertfolgen (42a-d) genau einer der Stützstellen (40a-d) zugeordnet ist. Raumkoordinaten von Oberflächenpunkten (44) auf der Oberfläche (81) werden dann basierend auf den durch das Maximieren der Korrelation für jeden der Bildpunkte (22, 32, 42, 52) als nächstliegend identifizierten Stützstellen (20a-d, 30a-d, 40a-d, 50a-d) bestimmt. Die Erfindung betrifft ferner eine Messvorrichtung (100) zum Durchführen dieses Verfahrens

Array-projected aperiodic sinusoidal fringes for high-speed 3D shape measurement

In recent years, the demands on three-dimensional (3-D) measurement systems have been getting higher, es- pecially concerning their speed. The use of a 3-D array projector enables measurement frame rates of up to the 100-kHz range. Our contribution introduces a new purpose-built setup that projects aperiodic sinusoidal fringes. We explain the 3-D measurement principle and the basic design of a 3-D array projector and describe the method how the desired aperiodic sinusoidal fringes are generated. We verify the consistency between specified and projected patterns and point out the results of the setups’s characterization, e.g., of its high-speed capability. Furthermore, first 3-D shape measurements at a projection frame rate of 3 kHz resulting in a 3-D frame rate of <330 Hz are presented and evaluated

3D reconstruction with single image pairs and structured light projection for short-term ultra-high-speed applications

A new approach for a 3D reconstruction algorithm using a single pair of a stereo-camera setup and a structured light projection based on spatial correlation is introduced. In comparison to existing methods using sequences of temporally consecutive images, sufficient 3D-reconstruction quality is achieved, even in the case of ultra-high-speed cameras. This is obtained by iterative application of correspondence finding and filtering operators. The calculation effort of the evaluation, filling, filtering, and outlier removing operators is relative high and may prevent a permanent application of the algorithm to high-resolution long-term recordings. The favored application scenario of the new method is the rough 3D reconstruction and motion tracking of quickly moving objects in short-term processes (few seconds), e.g. in the analysis of crash-test situations. Here, the complete recorded image sequence can be analyzed off-line which allows an afterwards optimization of the parameters. An advantage of the new technique regarding high-speed applications is that fixed single patterns instead of pattern sequences can be used for moving objects and hence no synchronization between projection and cameras is necessary

Vorrichtung und Verfahren zum räumlichen Vermessen von Oberflächen

The invention relates to a device for spatially measuring surfaces, comprising a projector (2) for projecting patterns into an object space, two cameras (3) for recording images of a surface (1) to be measured in the object space and a control and evaluation unit (5) for actuating the cameras (3) and for evaluating the images recorded therewith. The projector (2) comprises a light source (6), a projection lens (7) and at least one rotatably arranged pattern structure (8) as an imaging element, and also a drive (9) for rotating the at least one pattern structure (8), while the control and evaluation unit (5) is configured to carry out the following steps: - actuating the cameras (3) so that they simultaneously record one image at a multiplicity of successive recording times, such that a sequence of brightness values is captured for each point in image planes of the cameras (3), - identifying corresponding points (11) in the image planes of the cameras (3) by virtue of a correlation function being evaluated between the sequences of brightness values captured for potentially corresponding points and a value of a correlation thus formed being maximized, and - determining spatial coordinates of surface points (10) on the surface (1) by triangulation on the basis of the points (11) identified as corresponding to one another. Moreover, the invention relates to a corresponding method for measuring surfaces

Fast 3D Shape Measurement of Transparent Glasses by Sequential Thermal Fringe Projection

We present an approach for measuring the shape of transparent glasses, which enables us to significantly reduce the comparatively long measurement time while increasing the measurement accuracy. Instead of using area-like patterns, we irradiate the object to be measured successively in a locally strongly restricted area with considerably higher irradiance

Fast 3D Shape Measurement of Transparent Glasses by Sequential Thermal Fringe Projection

We present an approach for measuring the shape of transparent glasses, which enables us to significantly reduce the comparatively long measurement time while increasing the measurement accuracy. Instead of using area-like patterns, we irradiate the object to be measured successively in a locally strongly restricted area with considerably higher irradiance