Mesh normal consistency when no faces intersect

Summary: Corner case where there's nothing to do in this function.

Reviewed By: nikhilaravi

Differential Revision: D26073476

fbshipit-source-id: eb061683ffe35c1ffa8384c422a1557a636d52cd

pytorch3d/loss/mesh_normal_consistency.py

@@ -114,6 +114,11 @@ def mesh_normal_consistency(meshes):
             vert_edge_pair_idx, device=meshes.device, dtype=torch.int64
         )
 
+    if vert_edge_pair_idx.shape[0] == 0:
+        return torch.tensor(
+            [0.0], dtype=torch.float32, device=meshes.device, requires_grad=True
+        )
+
     v0_idx = edges_packed[edge_idx, 0]
     v0 = verts_packed[v0_idx]
     v1_idx = edges_packed[edge_idx, 1]

tests/test_mesh_normal_consistency.py

@@ -218,6 +218,17 @@ class TestMeshNormalConsistency(unittest.TestCase):
 
         self.assertTrue(torch.allclose(out1, out2))
 
+    def test_no_intersection(self):
+        """
+        Test Mesh Normal Consistency for a mesh known to have no
+        intersecting faces.
+        """
+        verts = torch.rand(1, 6, 2)
+        faces = torch.arange(6).reshape(1, 2, 3)
+        meshes = Meshes(verts=verts, faces=faces)
+        out = mesh_normal_consistency(meshes)
+        self.assertEqual(out.item(), 0)
+
     @staticmethod
     def mesh_normal_consistency_with_ico(
         num_meshes: int, level: int = 3, device: str = "cpu"