Hierarchical Bounding Volumes

Each primitive has an axis-aligned bounding cube. The hierarchical structure of the scene uses these cubes to create new bounding cubes at each internal node of the tree. These new cubes contain all of the children of the internal node. When a ray needs to be tested against the scene, it is only tested against a part of the tree if it intersects that part's bounding cube.

The image below is a balanced hierarchy of 16000 meshes, each with 26 faces. Meshes are expensive to test a ray against. The following statistics (computed for a non-antialiased version of the image below) show the benefits of the bounding volumes.

Using Hierarchical Bounding Volumes:

• Render time: 155s
• 262144 primary rays cast
• 107177 shadow rays cast
• 369321 total rays cast
• 471153 ray-primitive intersections
• Average primitive intersections per ray: 1.27573
• 22961933 ray-bounding box intersections
• Average bounding box intersections per ray: 62.1734

No Hierarchical Bounding Volumes:

• Render time: 37958s
• 262144 primary rays cast
• 107177 shadow rays cast
• 369321 total rays cast
• 5909136000 ray-primitive intersections
• Average primitive intersections per ray: 16000
• 0 ray-bounding box intersections
• Average bounding box intersections per ray: 0

Anti-aliased rendering of scene with 16 sets of 1000 meshes (each mesh with 26 faces) -- 416000 total faces.