small fix for iou3d

Summary:
A small numerical fix for IoU for 3D boxes, fixes GH #992

* Adds a check for boxes with zero side areas (invalid boxes)
* Fixes numerical issue when two boxes have coplanar sides

Reviewed By: nikhilaravi

Differential Revision: D33195691

fbshipit-source-id: 8a34b4d1f1e5ec2edb6d54143930da44bdde0906

pytorch3d/ops/iou_box3d.py

@@ -69,6 +69,28 @@ def _check_coplanar(boxes: torch.Tensor, eps: float = 1e-4) -> None:
     return
 
 
+def _check_nonzero(boxes: torch.Tensor, eps: float = 1e-4) -> None:
+    """
+    Checks that the sides of the box have a non zero area
+    """
+    faces = torch.tensor(_box_triangles, dtype=torch.int64, device=boxes.device)
+    # pyre-fixme[16]: `boxes` has no attribute `index_select`.
+    verts = boxes.index_select(index=faces.view(-1), dim=1)
+    B = boxes.shape[0]
+    T, V = faces.shape
+    # (B, T, 3, 3) -> (B, T, 3)
+    v0, v1, v2 = verts.reshape(B, T, V, 3).unbind(2)
+
+    normals = torch.cross(v1 - v0, v2 - v0, dim=-1)  # (B, T, 3)
+    face_areas = normals.norm(dim=-1) / 2
+
+    if (face_areas < eps).any().item():
+        msg = "Planes have zero areas"
+        raise ValueError(msg)
+
+    return
+
+
 class _box3d_overlap(Function):
     """
     Torch autograd Function wrapper for box3d_overlap C++/CUDA implementations.
@@ -138,6 +160,8 @@ def box3d_overlap(
 
     _check_coplanar(boxes1, eps)
     _check_coplanar(boxes2, eps)
+    _check_nonzero(boxes1, eps)
+    _check_nonzero(boxes2, eps)
 
     # pyre-fixme[16]: `_box3d_overlap` has no attribute `apply`.
     vol, iou = _box3d_overlap.apply(boxes1, boxes2)