Rainer Schütze

Increasing the accuracy of untaught robot positions by means of a multi-camera system

We aim to improve the absolute in line positional accuracy of a robot-guided effector to better than 1 mm. We do so using photogrammetric techniques and by relying heavily on simulations to fine tune each parameter and avoid weak configurations. We also use simulations to design an LED calibration object adapted to this application. A test procedure enables us to validate both the simulated results as well as the calibration procedure. The test results exceed expectations by improving the absolute positioning of a robot effector by a factor of 20.

Registration of 3D and Multispectral Data for the Study of Cultural Heritage Surfaces

We present a technique for the multi-sensor registration of featureless datasets based on the photogrammetric tracking of the acquisition systems in use. This method is developed for the in situ study of cultural heritage objects and is tested by digitizing a small canvas successively with a 3D digitization system and a multispectral camera while simultaneously tracking the acquisition systems with four cameras and using a cubic target frame with a side length of 500 mm. The achieved tracking accuracy is better than 0.03 mm spatially and 0.150 mrad angularly. This allows us to seamlessly register the 3D acquisitions and to project the multispectral acquisitions on the 3D model.

Asserting the precise position of 3d and multispectral acquisition systems for multisensor registration applied to cultural heritage analysis

We present a novel method to register multispectral acquisitions on a 3D model. The method is based on the external tracking of the acquisition systems using close-range photogrammetric techniques: multiple calibrated cameras simultaneously observe the successive acquisition systems in use. The views from these cameras are used to precisely determine the position of each acquisition system. All datasets can then be projected in the same coordinate system. The registration is thus independent from the quality and content of the data. This method is well suited to the study of cultural heritage or any other application where we do not wish to place targets on the object. We describe the method and the simulation pipeline used to find an adequate setup for two case studies.

Capture and processing of high resolution 3D-data of sutra inscriptions in China

Modern high resolution 3D-measuring techniques are widely used in quality control and industrial production, because they allow precise and reliable inspection of objects. Their potential to monitor surfaces, however, must not be restricted to industrial objects. Also in cultural heritage applications a detailed and reliable spatial description of surfaces is often useful and opens up new possibilities for conservation, analysis or presentation of objects. In the actual work we have considered Buddhistic stone inscriptions (8th- 12th centuries) which are important cultural assets of China. They need to be documented, analyzed, interpreted and visualized archaeologically, art-historically and text-scientifically. On one hand such buddhistic stone inscriptions have to be conserved for future generations but on the other hand further possibilities for analyzing the data could be enabled when the inscriptions would be accessible to a larger community, for instance the understanding of the historical growth of Buddhism in China. In this article we show innovative techniques for the documentation and analysis of stone inscriptions located in the province of Sichuan - south-west of china. The stone inscriptions have been captured using high precision 3D- measuring techniques what produces exact copies of the original inscriptions serving as base for further processing tasks. Typical processing might be directed towards an improvement of the legibility of characters or may try to automatically detect individual letters, to automatically identify certain text passages or even to characterize the written elements with respect to a potential style of the monk or the executing stonemason. All these processing steps will support the interpretation of the inscriptions by the sinologists involved with the analysis and evaluation of the texts. The concept and features of the image processing applied on the captured inscription as well as the aims and the effect of an interpretation based on algorithms for identifying and analyzing the inscriptions are demonstrated. In order to present the outcome to a large community, the results of the stone inscription reconstruction, the done interpretation and additional 2D / 3D maps are published within an interactive web platform.

Registration of arbitrary multi-view 3D acquisitions

To register 3D meshes representing smooth surfaces we track the 3D digitization system using photogrammetric techniques and calibrations. We present an example by digitizing a 800mmx600mm portion of a car door. To increase the tracking accuracy the 3D scanner is placed in a cubic frame of side 0.5m covered with 78 targets. The target frame moves in a volume that is approximately 1100mmx850mmx900mm, to digitize the area of interest. Using four cameras this target frame is tracked with of an accuracy of 0.03mm spatially and 0.180mrad angularly. A registration accuracy between 0.1mm and 2mm is reached. This method can be used for the registration of meshes representing featureless surfaces.

Preprocessing of region of interest localization based on local surface curvature analysis for three-dimensional reconstruction with multiresolution

We present an approach to integrate a preprocessing step of the region of interest ROI localization into 3-D scanners laser or ste- reoscopic. The definite objective is to make the 3-D scanner intelligent enough to localize rapidly in the scene, during the preprocessing phase, the regions with high surface curvature, so that precise scanning will be done only in these regions instead of in the whole scene. In this way, the scanning time can be largely reduced, and the results contain only per- tinent data. To test its feasibility and efficiency, we simulated the prepro- cessing process under an active stereoscopic system composed of two cameras and a video projector. The ROI localization is done in an itera- tive way. First, the video projector projects a regular point pattern in the scene, and then the pattern is modified iteratively according to the local surface curvature of each reconstructed 3-D point. Finally, the last pat- tern is used to determine the ROI. Our experiments showed that with this approach, the system is capable to localize all types of objects, including small objects with small depth.

Use of Local Surface Curvature Estimation for Adaptive Vision System Based on Active Light Projection

In this paper, we present a new 3D reconstruction approach based on local surface curvature analysis. Its integration can make a normal active stereoscopic system intelligent, and capable to produce directly optimized 3D model. The iterative 3D reconstruction process begins with a sparse and regular point pattern. Based on the reconstructed 3D point cloud, the local surface curvature around each 3D point is estimated. Those 3D points located in flat areas are removed from the 3D model, and a new pattern is created to project more points onto the object where there is high surface curvature. The 3D model is thus refined progressively during the acquisition process, and finally an optimized 3D model is obtained. Our numerous experiments showed that compared to the 3D models generated by commercial system, the loss of morphological quality is negligible, and the gain by the simplification of the model is considerable.