K. H. Strobl, E. Mair, T. Bodenmüller, S. Kielhöfer, W. Sepp, M. Suppa, D. Burschka, and G. Hirzinger.
The Self-Referenced DLR 3D-Modeler.
Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2009), St. Louis, MO, USA, pp. 21-28, October 2009, best paper finalist.
In the context of 3-D scene modeling, this work aims at the accurate estimation of the pose of a close-range 3-D modeling device, in real-time and passively from its own images. This novel development makes it possible to abandon using inconvenient, expensive external positioning systems. The approach comprises an ego-motion algorithm tracking natural, distinctive features, concurrently with customary 3-D modeling of the scene. The use of stereo vision, an inertial measurement unit, and robust cost functions for pose estimation further increases performance. Demonstrations and abundant video material validate the approach. |
BibTeX entry - Paper 
- Videos.
K. H. Strobl, W. Sepp, and G. Hirzinger.
On the Issue of Camera Calibration with Narrow Angular Field of View.
Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2009), St. Louis, MO, USA, pp. 309-315, October 2009.
This paper considers the issue of calibrating a camera with narrow angular field of view using standard, perspective methods in computer vision. In doing so, the significance of perspective distortion both for camera calibration and for pose estimation is revealed. Since narrow angular field of view cameras make it difficult to obtain rich images in terms of perspectivity, the accuracy of the calibration results is expectedly low. From this, we propose an alternative method that compensates for this loss by utilizing the pose readings of a robotic manipulator. It facilitates accurate pose estimation by nonlinear optimization, minimizing reprojection errors and errors in the manipulator transformations at the same time. Accurate pose estimation in turn enables accurate parametrization of a perspective camera. |
BibTeX entry - Paper .
E. Mair, K. H. Strobl, M. Suppa, and D. Burschka.
Efficient Camera-Based Pose Estimation for Real-Time Applications.
Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2009), St. Louis, MO, USA, pp. 2696-2703, October 2009.
Accurate online localization is crucial for mobile robotics. In this paper, we describe a real-time image-based localization technique, which is based on a single calibrated camera. This can be supported by a second camera to improve accuracy and to provide the proper translational scale. The system aims for a robust and unbiased pose estimation on highly dynamic and resource-limited systems, requiring the following steps: The robustness of the applied pose estimation technique has been significantly improved, a novel approach for stereo subpixel accurate landmark initialization is used and the conventional tracking routines have been sped up to achieve online capability. Although, the algorithm is designed for accurate, online short-range egomotion estimation for hand-held 3D scanning, it can be used for any mobile robot application. Various tests and experimental results with a mobile platform and a hand-held 3D modeler are presented and discussed. |
F. Lange, K. H. Strobl, J. Langwald, S. Jörg, G. Hirzinger, B. Gruber, J. Klein, and J. Werner.
Kameragestützte Montage von Rädern an kontinuierlich bewegte Fahrzeuge.
VDI-Berichte 2012 (Robotik 2008), Munich, Germany, pp. 155-158, June 2008, in German.
Betrachtet wird die Montage von Rädern an ein durch ein Förderband transportiertes Fahrzeug. Dazu nimmt ein Industrieroboter Rad und Schrauben auf und führt sie zum Fügen an das Fahrzeug, dessen Radnabe während der Bewegung in allen 6 Freiheitsgraden durch eine robotergeführte Kamera vermessen wird. Die Kamera ist mit einer Ringleuchte ausgestattet und hinter dem Achsloch des gehaltenen Rades angeordnet, das dadurch auch bei schwingender Karosse robust an die Radnabe herangeführt und kraftgeregelt verschraubt wird. |
BibTeX entry - Abstract - Paper .
K. H. Strobl and G. Hirzinger.
More Accurate Camera and Hand-Eye Calibrations with Unknown Grid Pattern Dimensions.
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA 2008), Pasadena, California, USA, pp. 1398-1405, May 2008.
This paper presents two novel approaches for accurate intrinsic and extrinsic camera calibration. The rationale behind them is the widespread violation of the traditional assumption that the metric structure of the calibration object is perfectly known. A novel formulation parameterizes a checkerboard calibration pattern in such a way that the calibration performs optimally irrespective of its actual dimensions. Simulations and experiments show that it is very rare for traditional calibration methods to come by the accuracy readily attained by this approach. |
BibTeX entry - Paper .
M. Suppa, S. Kielhoefer, J. Langwald, F. Hacker, K. H. Strobl, and G. Hirzinger.
The 3D-Modeller: A Multi-Purpose Vision Platform.
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA 2007), Rome, Italy, pp. 781-787, April 2007.
This paper deals with the concept and implementation of a multi-purpose vision platform. In robotics, numerous applications require perception. A multi-purpose vision platform suited for object recognition, cultural heritage preservation and visual servoing at the same time is missing. In this work, we draw attention to the design principles for such a vision platform. We present its implementation, the 3D-Modeller. In specifying and combining multiple sensors, laser-range scanner, laser-stripe profiler and stereo vision, we derive the required mechanical and electrical hardware design. The concepts for synchronization and communication round off our approach. Precision and frame rate are presented. We illustrate the versatility of the 3D-Modeller by addressing four applications: 3D-modeling, exploration, tracking and object recognition. Due to its low weight and generic mechanical interface, it can be mounted on industrial robots, humanoids, or free-handed as well. The 3D-Modeller is flexibly applicable, not only in research but also in industry, especially in small batch assembly. |
K. H. Strobl and G. Hirzinger.
Optimal Hand-Eye Calibration.
Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2006), Beijing, China, pp. 4647-4653, October 2006.
This paper presents a calibration method for eye-in-hand systems in order to estimate the hand-eye and the robot-world transformations. The estimation takes place in terms of a parametrization of a stochastic model. In order to perform optimally, a metric on the group of the rigid transformations SE(3) and the corresponding error model are proposed for nonlinear optimization. This novel metric works well with both common formulations AX=XB and AX=ZB, and makes use of them in accordance with the nature of the problem. The metric also adapts itself to the system precision characteristics. The method is compared in performance to earlier approaches. |
BibTeX entry - Paper .
K. H. Strobl, W. Sepp, E. Wahl, T. Bodenmüller, M. Suppa, J. F. Seara, and G. Hirzinger.
The DLR Multisensory Hand-Guided Device: The Laser Stripe Profiler.
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA 2004), New Orleans, LA, USA, pp. 1927-1932, April 2004.
This paper presents the DLR Laser Stripe Profiler as a component of the DLR multisensory Hand-Guided Device for 3D modeling. After modeling the reconstruction process, we propose a novel method for laser plane self-calibration based on the assessment of the deformations the miscalibration leads to. In addition, the requirement for absence of optical filtering implies the development of a robust stripe segmentation algorithm. Experiments demonstrate the validity and applicability of the approaches. |
BibTeX entry - Paper - Videos (DivX): Meshing, Calibration.
J. F. Seara, K. H. Strobl, E. Martin, and G. Schmidt.
Task-Oriented and Situation-Dependent Gaze Control for Vision Guided Humanoid Walking.
Proceedings of the 3rd IEEE-RAS International Conference on Humanoid Robots (Humanoids2003), Munich and Karlsruhe, Germany, October 2003.
This article presents various aspects of a gaze control scheme for visually guided humanoid robot navigation. A modular task-oriented and situation dependent gaze control architecture is proposed. It comprises three major modules: (I) Information Management, (II) Task-specific Gaze Strategy, and (III) Decision Scheme. The strategy is based on the maximization of the predicted visual information. For the information management a coupled hybrid Extended Kalman Filter is employed. Specific view direction control strategies for two concurrent objectives of different nature, obstacle avoidance and self-localization, have to be weighted and pursued in parallel. The main goal of this work is to formalize and implement a decision strategy in order to achieve an intelligent task-oriented active vision system for a biped walking robot. It intends to explain the active vision decision making problem: Where to look next?, of an agent facing multiple goals. The general approach rests upon the definition of a set of Utility Functions over the outcomes of the set of possible view directions. Next the various utility functions, i.e.Agents, representing different kinds of preference rankings over the predicted outcomes, are organized to solve the Action/Selection problem as a Society of Minds. |
BibTeX entry - Paper
J. F. Seara, K. H. Strobl, and G. Schmidt.
Path-Dependent Gaze Control for Obstacle Avoidance in Vision Guided Humanoid Walking.
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA 2003), Taipei, Taiwan, pp. 887-892, September 2003.
This article presents a novel gaze control strategy for obstacle avoidance in the context of vision guided humanoid walking. The generic strategy is based on the maximization of the predicted visual information. For information/uncertainty management a new hybrid formulation of an Extended Kalman Filter is employed. The performance resulting from this view direction control scheme shows the dependence of the intelligent gazing behavior on the pre-planned local path. |
BibTeX entry - Paper
J. F. Seara, K. H. Strobl, and G. Schmidt.
Information Management for Gaze Control in Vision Guided Biped Walking.
Proceedings of the IEEE/RSJ/GI International Conference on Intelligent Robots and Systems (IROS 2002), Lausanne, Switzerland, pp. 31-36, October 2002.
This article deals with the information management for active gaze control in the context of vision--guided humanoid walking. The proposed biologically inspired predictive gaze control strategy is based on the maximization of visual information. The quantification of the information requires a stochastic model of both, the robot and perception system. The information/uncertainty management, i.e. relationship between system state estimation and the active measurements, employs a coupled (considering cross-covariances) hybrid (reflecting the discontinuous character of biped walking) Extended (copes with non-linear systems) Kalman Filter approach. |
BibTeX entry - Paper
O. Lorch, J. F. Seara, K. H. Strobl, U. D. Hanebeck, and G. Schmidt.
Perception Errors in Vision Guided Walking: Analysis, Modeling, and Filtering.
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA 2002), Washington DC, USA, pp. 2048-2053, May 2002.
This article deals with specific aspects concerning the visual perception process of a humanoid walking machine. An active vision system provides the information about the environment necessary for autonomous goal-oriented locomotion. Due to errors in each stage of the perception process, ideal environment reconstruction is not possible. By modeling these errors, stochastic components can be compensated using a hybrid Extended Kalman Filter approach with an alternating reference frame, thus reflecting the discontinuous character of biped walking. The perception results improved by filtering can be used for the autonomous locomotion of the robot. Experiments with the walking machine BARt-UH demonstrate the validity of our approach. |
BibTeX entry - Paper
J. F. Seara, O. Lorch, and G. Schmidt.
Gaze Control for Goal-Oriented Humanoid Walking.
Proceedings of the 2nd IEEE-RAS International Conference on Humanoid Robots (Humanoids2001), Waseda, Tokio, Japan, pp. 187-195, November 2001.
In this article a predictive task-dependent gaze control strategy for goal-oriented humanoid walking is presented. In the context of active vision systems we introduce an information theoretical approach for maximization of visual information. Based on two novel concepts, Information Content of a view situation and Incertitude, we present a method for selecting optimal subsequent view directions, thus contributing to an improved performance in typical autonomous robot locomotion tasks. Simulations and experimental results dealing with the duality of different tasks during locomotion, i.e. obstacle avoidance and self localization, prove the applicability of our approach on humanoid walking machines. |
BibTeX entry - Paper