When the space of the objects we are computing collision for is complex, a single bounding volume manymay not provide tight enough approximation to considerably reduce the number of exact collision detections we have to perform. In such cases [[Bounding volume hierarchy| Bounding Volume Hierarchy]] (BVH) may be used. A BVH is a tree structure over a set of bounding volumes. BVH can be used with deformable objects such as cloth or soft-bodies but the volume hierarchy has to be adjusted as the shape deforms. For deformable objects we need to be concerned about self-collisions or self intersections. BVH can be used for that end as well. Collision between two objects is computed by computing intersection between the bounding volumes of the root of the tree as there are collision we dive into the sub-trees that intersect. Exact collisions between the actual objects, or its parts (often triangles of a [[triangle mesh]]) need to be computed only between intersecting leaves. The same approach works for pair wise collision and self-collisions.
