[Fix] Fix horizontal boxes (#9140)

* Fix corner2hbox of HorizontalBoxes for supporting empty bboxes. * Test empty boxes for HorizontalBoxes
open-mmlab · Nov 2, 2022 · 5897b32 · 5897b32
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diff --git a/mmdet/structures/bbox/horizontal_boxes.py b/mmdet/structures/bbox/horizontal_boxes.py
@@ -227,6 +227,8 @@ def corner2hbox(corners: Tensor) -> Tensor:
         Returns:
             Tensor: Horizontal box tensor with shape of (..., 4).
         """
+        if corners.numel() == 0:
+            return corners.new_zeros((0, 4))
         min_xy = corners.min(dim=-2)[0]
         max_xy = corners.max(dim=-2)[0]
         return torch.cat([min_xy, max_xy], dim=-1)

diff --git a/tests/test_structures/test_bbox/test_horizontal_boxes.py b/tests/test_structures/test_bbox/test_horizontal_boxes.py
@@ -123,6 +123,9 @@ def test_project(self):
         boxes2.translate_([x_translate, y_translate])
         boxes2.rescale_([scale_factor, scale_factor])
         assert_allclose(boxes1.tensor, boxes2.tensor)
+        # test empty boxes
+        empty_boxes = HorizontalBoxes(torch.zeros((0, 4)))
+        empty_boxes.project_(matrix)
 
     def test_rescale(self):
         scale_factor = [0.4, 0.8]