A binary data file created by oconv and read by rpict, contains the octree data structure, which is used to speed up the ray-tracing algorithm. If the resultant image is a luminance image the octree file is used in the calculation of glare. For illuminance images the octree file can be discarded when the image has been created.
An octree is a data structure that subdivides a cubic volume of space into eight sub-cubes, each of which may be subdivided into eight sub-cubes, and so on recursively. This data structure is created by the program oconv and is used to speed up ray intersection tests on the scene. This data structure is stored in the octree file.
