A two-step approach is presented to generate a 3D navigable terrain model for robots operating in natural and uneven environment. First an unstructured surface is built from a 360 degrees field of ...view LIDAR scan. Second the reconstructed surface is analyzed and the navigable space is extracted to keep only the safe area as a compressed irregular triangular mesh. The resulting mesh is a compact terrain representation and allows point-robot assumption for further motion planning tasks. The proposed algorithm has been validated using a large database containing 688 LIDAR scans collected on an outdoor rough terrain. The mesh simplification error was evaluated using the approximation of Hausdorff distance. In average, for a compression level of 93.5%, the error was of the order of 0.5 cm. This terrain modeler was deployed on a rover controlled from the International Space Station (ISS) during the Avatar Explore Space Mission carried out by the Canadian Space Agency in 2009.
The paper proposes a set of visual odometry and terrain reconstruction algorithms for quadruped robot in unstructured environments. Visual odometry can accurately measure the change value of the ...robot body's 6 degrees of freedom in 3D space. Terrain reconstruction can aid the robot to determine foot location around obstacles. With the visual odometry, the robot can remember the obstacle position even if the obstacles are out of vision. In order to simplify the process, two parts will also use the same sparse stereo visual image processing methods. The detail of the algorithms and the implementation process are introduced briefly. At last, the experiment results show that the algorithms are accurate and robust for quadruped robot navigation.
Future planetary landers must be capable of detecting hazards in the landing zone and maneuvering to a new and safe site, for the requirements of the scientific task. This paper presents an ...autonomous hazard detection and avoidance method based on Lyapunov control method for planetary landing. The terrain of the landing zone is first reconstructed using the feature points of pictures at two different time, and the plane of the landing zone was determined by fitting the terrain elevation data. Then, hazards in the landing zone were identified according to the vitual plane. In order to reduce the potential threats by the hazards, an avoidance control law is designed using Lyapunov function method. The control law can guarantee the landers reach the safe site, simultaneously decrease the landing speed to zero. The results of numerical simulation show that the method is satisfactory for hazards detection and avoidance with assumed environments.
This paper presents the problem of reconstructing the 3D terrain model for landing of small body spacecraft, in order to approach and land on a small body successfully. We propose an on-line terrain ...modeling using image sequence provided by an on-board camera. The recursive structure from motion algorithm and the orthography factorization algorithm are proposed to recover the depth maps. The application range and reconstruction precision of the two different methods are demonstrated by the experimental results. It is shown that the has recursive structure from motion algorithm has a higher accuracy, while the orthography factorization algorithm is more robust.
To efficiently represent large artificial terrains on today's graphic hardwares, we propose a new terrain rendering scheme with hierarchical triangular patches and pre-constructed match ing blocks. ...It renders terrain patches at different LODs(levels-of-details) according to the current visual requirement. The hierarchical structure can reduce the total number of 'draw primitive(DirectX)' calls significantly by replacing a large set of triangles with a single patch where appropriate while other conventional methods try to reduce the total number of primitives to be rendered. After the initial construction of patches, the new scheme does not re-triangulate during runtime, further enhancing its performance. We also propose a specially designed matching method to eliminate cracks on the boundaries between neighboring patches. It constructs a few matching blocks at initialization with which it replaces original patches on boundaries where cracks may occur.
In this paper a method to perform a smooth three-dimensional reconstruction from a contour map of a terrain is presented. The input data to the proposed method is 3D points of polygonal lines that ...represent contour maps with the elevation information included; such data is available at INEGI in the case of Mexico. The obtained 3D reconstruction is represented by a triangle mesh. The main idea of the proposed method is to include intermediate points among contour lines to avoid the problem of flat triangles, thus a good reconstruction with smooth changes in its surface can be achieved. The intermediate points are selected from the skeleton of the contour lines, and their heights are calculated automatically. The method is tested with simulated data to shown its effectiveness.
High quality, artifact-free fitting a bathymetry (sea-floor) surface to very unevenly spaced depth data from ship tracklines is possible with ODETLAP (Overdetermined Laplacian Partial Differential ...Equation). The problem is that many data points, but with imprecise values, can be collected along and near the ships, e.g., with Multibeam Bathymetry, but there are no data between the tracklines, which may be a considerable distance apart. The numerous artifacts of previous surface fitting algorithms were so totally unacceptable that even Photoshop has been used to smooth them. In contrast, the implementation of this version of ODETLAP generates surfaces that do not exhibit artifacts even when displayed with techniques that highlight minor slope irregularities, which is, in the authors' opinion, the most appropriate evaluation metric. Since the data is imprecise, ODETLAP's surface approximates, rather than interpolates, the data. ODETLAP can trade off smoothness and accuracy to capture the small features that are not artifacts. This extension to ODETLAP is a variable smoothness parameter so that points distant from a known depth are smoothed differently from points close to a known depth. The broader implication is that ODETLAP is a very powerful algorithm with many applications. The Matlab implementation is freely available for nonprofit research and education.
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