Research On Real Time Collision Detection In Virtual Prototype Evironment

Collision detection is one of the basic problems of computer simulation based motion planning, virtual manufacturing, virtual prototype, et al. In 3d CAD based virtual prototype environment, it has important practical significance for solving the related problems of product design to research collision detection among multi-body system. In the paper, collision detection theory is the basis, and virtual prototype of locomotive and railway vehicle is application background. The further study and development on collision detection will provide reliable basis for product design based on virtual prototype. It will also as a reference for research on related field. The main research contents include the following.(1) The research status of collision detection is summarized and the characteristics and shortages of recent research are analyzed, and research contents and methods of the paper are proposed.(2) The collision detection algorithm based on Oriented Bounding Box (OBB) are researched and implemented, and three improvements have been made. The first, a fast intersection algorithm between spatial triangles is proposed, in which the linear dependence of edge vector of triangle, linear characteristics of matrix calculation and projection characteristics of graphics are fully used to improve the performance. Theoretical analysis and experimental verification show that the algorithm proposed is better than other's in the occasions with high triangle-triangle intersection ration, and is chime with other algorithm in the occasions with low intersection ration. In the collision detection algorithm based on bounding box, the intersection ration of triangles is high, therefore it is helpful to improve the performance of the collision detection algorithm. The second, a hybrid bounding box is constructed on top level of OBB hierarchical tree to eliminate the obviously disjoint object quickly, which improve the performance of algorithm, especially in large sparse scene. The costs of construction and test are all least. The last, according to motion coherence, the collision message of previous frame is buffered to detect the collision of current frame, which also improve the performance of algorithm. Testing results show that these improvements are efficient and successful, and which have improved the performance of algorithm.(3) A General-Purpose computation on GPUs (GPGPU) based collision detection algorithm is designed and implemented. The parallel and fast computation of graphics hardware is fully used, and all computation of algorithm is performed on GPU. Firstly, bounding boxes message and geometric message of models are mapped into textures and download to GPU. Then, the principle of render is used for computation. Therefore, the collision detection results are output to texture using off-screen rending technology. Lastly, the data on texture are read to CPU for next operation. All computation of algorithm is performed on GPU, so only two data exchanges between CPU and GPU are executed, one for downloading to GPU, and the other for reading to CPU. This method avoids the bottleneck of data transmission. Testing results show this algorithm keep the collision detection precision of the same kind algorithm performed on CPU. In simple case, the performance of this algorithm is worse than the same kind algorithm performed on CPU. But in complex case, this algorithm has obvious advantage than the later.(4) An image based collision detection algorithm is proposed and implemented. Using the intersection characteristic between ray and closed object, the times of the ray intersecting with front and back of the object are recorded to detect the collision of target objects with the aid of stencil buffer and depth buffer. Vertex Buffer Object (VBO) is used to raise drawing speed greatly and also the detection speed, for target objects need to be redrawn one more times in image based collision detection algorithm. Another way to improve performance is using bounding box to computer the intersection field, which can reduce the point number needed to be drawn. Testing results show that the algorithm can deal with the closed object effectively and powerfully, especially for complex models. The collision detection precision and speed however are affected by graphics hardware.(5) The advantages and disadvantages of graphics-based and image-based collision detection algorithm as wel as load balancing of CPU and GPU are analyzed. A graphics-based and image-based hybrid algorithm is proposed and implemented. According to the number of the target objects in the scene, a graphics-based (on CPU) or image-based (on GPU) collision detection between bounding box of object is chosen automatically, and then the Rough Collide Sets (RCS) is constructed. Next step, an image-based collision detection algorithm among surface is used to generate Accurate Collide Sets (ACS). At last, graphics-based triangles intersections in ACS are performed and the results are returned. In triangles intersections testing, the performance of GPGPU-based and CPU-based algorithm is analyzed in different scales, and according to the scales, a suitable algorithm can be choosed automatically by the software. Testing results show that the algorithm keeps the advantages of image-based algorithm, such as fastness and stationarity, and the advantages of graphics-based algorithm, such as accuracy and obtaining collision point easily. This algorithm strikes compromise between precision and speed.(6) The OBB-based collision detection improved algorithm named FRCD is applied to the visual dynamics simulation platform based on CAD model to detect the intersection among complex CAD models of railway vehicle main parts when them running. The dynamics analysis and visual 3D kinematics simulation are all based CAD model, and executed synchronistically. This method which includes digital analysis and visual 3D simulation will provide comprehensive reference for the dynamics parameters and structure design of railway vehicles.Based on these research and development, traditional algorithms are improved and some new algorithms are proposed. All these algorithms provide the technology basis for developing and perfecting visual platform of railway vehicle virtual prototype. It also provides reference for collision detection research in related field.