Scene Graph - Scene Graphs and Bounding Volume Hierarchies (BVHs)

Scene Graphs and Bounding Volume Hierarchies (BVHs)

Bounding Volume Hierarchies (BVHs) are useful for numerous tasks — including efficient culling and speeding up collision detection between objects. A BVH is a spatial structure, but doesn't have to partition the geometry (see spatial partitioning below).

A BVH is a tree of bounding volumes (often spheres, axis-aligned bounding boxes or oriented bounding boxes). At the bottom of the hierarchy, the size of the volume is just large enough to encompass a single object tightly (or possibly even some smaller fraction of an object in high resolution BVHs). As one ascends the hierarchy, each node has its own volume that tightly encompasses all the volumes beneath it. At the root of the tree is a volume that encompasses all the volumes in the tree (the whole scene).

BVHs are useful for speeding up collision detection between objects. If an object's bounding volume does not intersect a volume higher in the tree, it cannot intersect any object below that node (so they are all rejected very quickly).

Obviously, there are some similarities between BVHs and scene graphs. A scene graph can easily be adapted to include/become a BVH — if each node has a volume associated or there is a purpose-built 'bound node' added in at convenient location in the hierarchy. This may not be the typical view of a scene graph, but there are benefits to including a BVH in a scene graph.