add some notes

cubvh/api.py

@@ -18,6 +18,7 @@ class cuBVH():
         if torch.is_tensor(vertices): vertices = vertices.detach().cpu().numpy()
         if torch.is_tensor(triangles): triangles = triangles.detach().cpu().numpy()
 
+        # check inputs
         assert triangles.shape[0] > 8, "BVH needs at least 8 triangles."
         
         # implementation

readme.md

@@ -24,6 +24,7 @@ import cubvh
 
 ### build BVH from mesh
 mesh = trimesh.load('example.ply')
+# NOTE: you need to normalize the mesh first, since the max distance is hard-coded to 10.
 BVH = cubvh.cuBVH(mesh.vertices, mesh.faces) # build with numpy.ndarray/torch.Tensor
 
 ### query ray-mesh intersection

src/bvh.cu

@@ -411,6 +411,7 @@ public:
         for (uint32_t i = 0; i < N_STAB_RAYS; ++i) {
             // Use a Fibonacci lattice (with random offset) to regularly
             // distribute the stab rays over the sphere.
+            // ref: http://extremelearning.com.au/how-to-evenly-distribute-points-on-a-sphere-more-effectively-than-the-canonical-fibonacci-lattice/
             Vector3f d = fibonacci_dir<N_STAB_RAYS>(i, offset);
 
             // If any of the stab rays goes outside the mesh, the SDF is positive.