@inproceedings{SchmidtVogtNiemann2002, author = {Schmidt, Jochen and Vogt, F. and Niemann, H.}, title = {Nonlinear Refinement of Camera Parameters using an Endoscopic Surgery Robot}, series = {Proceedings of IAPR Conference on Machine Vision Applications (MVA)}, booktitle = {Proceedings of IAPR Conference on Machine Vision Applications (MVA)}, year = {2002}, abstract = {We present an Approach for non linea roptimization of the parameters of an endoscopic camera mounted on a surgery robot. The goal is to generate a depth map for each image in order to enhance the quality of medical light fields. The pose information provided by the robot is used as an initialization, where especially the orientation isi naccurate. Refinement of intrinsic and extrinsic camera parameters is performed by minimizing the back-projectionerror of 3-D points that are reconstructed by triangulation from image Feature stracked over an image sequence. Optimization of the camera parameters results in an enhancement of Rendering Quality in two ways: More accurate parameters lead to better interpolation as well as to better depth maps for approximating the scenegeometry.}, language = {en} } @inproceedings{SchmidtNiemannVogt2002, author = {Schmidt, Jochen and Niemann, H. and Vogt, F.}, title = {Dense Disparity Maps in Real-Time with an Application to Augmented Reality}, series = {Proceedings Sixth IEEE Workshop on Applications of Computer Vision (WACV 2002), pages 225-230, Orlando, FL USA}, booktitle = {Proceedings Sixth IEEE Workshop on Applications of Computer Vision (WACV 2002), pages 225-230, Orlando, FL USA}, year = {2002}, abstract = {This work presents a technique for computing dense disparity maps from a binocular stereo camera system. The methods are applied in an Augmented Reality setting for combining real and virtual worlds with proper occlusions. The proposed stereo correspondence technique is based oil area matching and facilitates an efficient strategy by using the concept of a three-dimensional similarity accumulator whereby occlusions are detected and object boundaries are extracted correctly. The main contribution of this paper is the way we fill the accumulator using absolute differences of images and computing a mean filter on these difference images. This. is. where the main advantages of the accumulator approach can be exploited, since all entries can be computed in parallel and thus extremely efficient. Additionally, we-perform an asymmetric correction step and a post-processing of the disparity maps that maintains object edges.}, language = {en} } @inproceedings{SchmidtVogtNiemann2005, author = {Schmidt, Jochen and Vogt, F. and Niemann, H.}, title = {Calibration-Free Hand-Eye Calibration: A Structure-from-Motion Approach}, series = {Joint Pattern Recognition Symposium}, booktitle = {Joint Pattern Recognition Symposium}, publisher = {Springer}, address = {Berlin}, year = {2005}, abstract = {The paper presents an extended hand-eye calibration approach that, in contrast to the standard method, does not require a calibration pattern for determining camera position and orientation. Instead, a structure-from-motion algorithm is applied for obtaining the eye-data that is necessary for computing the unknown hand-eye transformation. Different ways of extending the standard algorithm are presented, which mainly involves the estimation of a scale factor in addition to rotation and translation. The proposed methods are experimentally compared using data obtained from an optical tracking system that determines the pose of an endoscopic camera. The approach is of special interest in our clinical setup, as the usage of an unsterile calibration pattern is difficult in a sterile environment.}, language = {en} } @inproceedings{SchmidtVogtNiemann2005, author = {Schmidt, Jochen and Vogt, F. and Niemann, H.}, title = {Vector Quantization Based Data Selection for Hand-Eye Calibration}, series = {Vision, Modeling, and Visualization 2004, pages 21-28, Stanford, USA}, booktitle = {Vision, Modeling, and Visualization 2004, pages 21-28, Stanford, USA}, year = {2005}, abstract = {The paper presents a new vectorquantization based Approach for selecting well-suited data for hand-eye calibration from a given sequence of hand and eye movements. Data selection is essential if control of the movements used for calibration is not possible, especially when using continuously recorded data. The new algorithm is compared to another method for data selection as well as to the processing of subsequent movements. Experimental results on real and synthetic data sets show the superior performance of the new approach with respect to calibration errors and computation time. Real data has been obtained from an optical tracking system and a camera mounted on an endoscope, the goal being the reconstruction of medical lightfields.}, language = {en} } @article{VogtKruegerSchmidtetal.2004, author = {Vogt, F. and Kr{\"u}ger, S. and Schmidt, Jochen and Paulus, D. and Niemann, H. and Hohenberger, W. and C. H., Schick}, title = {Light Fields for Minimal Invasive Surgery Using an Endoscope Positioning Robot}, series = {Methods of Information in Medicine}, journal = {Methods of Information in Medicine}, year = {2004}, abstract = {OBJECTIVES: To generate a fast and robust 3-D visualization of the operation site during minimal invasive surgery. METHODS: Light fields are used to model and visualize the 3-D operation site during minimal invasive surgery. An endoscope positioning robot provides the position and orientation of the endoscope. The a priori un-known transformation from the endoscope plug to the endoscope tip (hand-eye transformation) can either be determined by a three-step algorithm, which includes measuring the endoscope length by hand or by using an automatic hand-eye calibration algorithm. Both methods are described in this paper and their respective computation times and accuracies are compared. RESULTS: Light fields were generated during real operations and in the laboratory. The comparison of the two methods to determine the unknown hand-eye transformation was done in the laboratory. The results which are being presented in this paper are: rendered images from the generated light fields, the calculated extrinsic camera parameters and their accuracies with respect to the applied hand-eye calibration method, and computation times. CONCLUSION: Using an endoscope positioning robot and knowing the hand-eye transformation, the fast and robust generation of light fields for minimal invasive surgery is possible.}, language = {en} } @inproceedings{SchmidtVogtNiemann2003, author = {Schmidt, Jochen and Vogt, F. and Niemann, H.}, title = {Robust Hand-Eye Calibration of an Endoscopic Surgery Robot Using Dual Quaternions}, series = {Pattern Recognition, Proceedings of the 25th DAGM Symposium, Magdeburg}, booktitle = {Pattern Recognition, Proceedings of the 25th DAGM Symposium, Magdeburg}, year = {2003}, abstract = {This paper presents an approach for applying a dual quaternion hand-eye calibration algorithm on an endoscopic surgery robot. Special focus is on robustness, since the error of position and orientation data provided by the robot can be large depending on the movement actually executed. Another inherent problem to all hand-eye calibration methods is that non-parallel rotation axes must be used; otherwise, the calibration will fail. Thus we propose a method for increasing the numerical stability by selecting an optimal set of relative movements from the recorded sequence. Experimental evaluation shows the error in the estimated transformation when using well-suited and ill-suited data. Additionally, we show how a RANSAC approach can be used for eliminating the erroneous robot data from the selected movements.}, language = {en} }