Fix issues woth inplace modification of tensors in BaseInstance3DBoxes (#283)

mmdet3d/core/bbox/structures/base_box3d.py

@@ -57,7 +57,7 @@ class BaseInstance3DBoxes(object):
         else:
             self.box_dim = box_dim
             self.with_yaw = with_yaw
-        self.tensor = tensor
+        self.tensor = tensor.clone()
 
         if origin != (0.5, 0.5, 0):
             dst = self.tensor.new_tensor((0.5, 0.5, 0))

mmdet3d/core/bbox/structures/cam_box3d.py

@@ -63,7 +63,7 @@ class CameraInstance3DBoxes(BaseInstance3DBoxes):
         else:
             self.box_dim = box_dim
             self.with_yaw = with_yaw
-        self.tensor = tensor
+        self.tensor = tensor.clone()
 
         if origin != (0.5, 1.0, 0.5):
             dst = self.tensor.new_tensor((0.5, 1.0, 0.5))