Measuring BVH Quality

[ghost]

Just out of curiosity, is there any metrics that this library can calculate that indicate the quality of the generated BVHs aside from the traversal performance? Perhaps like the accumulative amount of empty space between parent and sub nodes? I don't think I've seen this measured before in other projects, but it seems like it would be a useful metric for comparisons between algorithms.

[madmann91]

There's the SAH, of course. Computing it is relatively easy (see https://github.com/madmann91/bvh/blob/master/include/bvh/parallel_reinsertion_optimization.hpp#L34). That's what the 'ParallelReinsertionOptimization' class is using to optimize the tree. Keep in mind that even though that's the 'best' measure that can be used during construction, and even though it correlates really well to performance, it's not an absolute measure of quality. There are trees with lower SAH than others that will perfom better in practice. There's this very informative paper if you are interested in quality metrics: https://research.nvidia.com/publication/quality-metrics-bounding-volume-hierarchies.
If you really need that, I can add a class that computes the SAH.

[ghost]

I'll have to give that article a read then. I don't really know what the effort is required to do this, so if it's a bit too much than I'd rather just stick with traversal time as the best metric.

[madmann91]

I have added a SahBasedAlgorithm class that allows computing the SAH of a given BVH. To use it, you first have to derive from it, and set the traversal_cost variable to the ratio Ct/Ci, where Ct is the cost of traversing a node (performing a ray-node intersection), and Ci is the cost of intersecting a primitive. I took the liberty to close this issue, but please re-open it if that does not satisfy your needs.

[ghost]

That definitely does! Thank you so much!