Interactive and continuous collision detection for avatars in virtual environments

We present a fast algorithm for continuous collision detection between a moving avatar and its surrounding virtual environment. We model the avatar as an articulated body using line-skeletons with constant offsets and the virtual environment as a collection of polygonized objects. Given the position and orientation of the avatar at discrete time steps, we use an arbitrary in-between motion to interpolate the path for each link between discrete instances. We bound the swept-space of each link using a swept volume (SV) and compute a bounding volume hierarchy to cull away links that are not in close proximity to the objects in the virtual environment. We generate the SV's of the remaining links and use them to check for possible interferences and estimate the time of collision between the surface of the SV and the objects in the virtual environment. Furthermore, we use graphics hardware to perform collision queries on the dynamically generated swept surfaces. Our overall algorithm requires no precomputation and is applicable to general articulated bodies. We have implemented the algorithm on a 2.4 GHz Pentium IV PC with NVIDIA GeForce FX 5800 graphics card and applied it to an avatar with 16 links, moving in a virtual environment composed of hundreds of thousands of polygons. Our prototype system is able to detect all contacts between the moving avatar and the environment in 10 - 30 milliseconds.