Bugs in ops.mesh.check_sign() triggered under special circumstances

Bugs in ops.mesh.check_sign() triggered under special circumstances

We found that if a point is in a sepcific axis, the check_sign is invalid for some primitive meshes.

from kaolin.ops.mesh import check_sign, index_vertices_by_faces
import trimesh as tm
import torch
# we test the check_sign function
x_points = torch.Tensor([[[1, 0, 0]]])
y_points = torch.Tensor([[[0, 1, 0]]])
z_points = torch.Tensor([[[0, 0, 1]]])
# e.g. When the test primitive is Sphere, check_sign is incorrect on x/y-axis
sphere_mesh = tm.primitives.Sphere(radius=2.0, subdivision=3)
points = z_points
print(f'trimesh contains() result: {sphere_mesh.contains(points.squeeze(0))}')
print(f'check_sign() result: {check_sign(torch.Tensor(sphere_mesh.vertices).unsqueeze(0), torch.Tensor(sphere_mesh.faces).long(), points)}')

Note that the cast a ray from the point is a really smart idea, and it is valid for most of points in our test, we don't know if this is an imperfection in the implementation.