Temporarily fix docstring of three coordinate systems to reduce confusion. (#457)

mmdet3d/core/bbox/structures/cam_box3d.py

@@ -13,7 +13,7 @@ class CameraInstance3DBoxes(BaseInstance3DBoxes):
 
     .. code-block:: none
 
-                z front (yaw=0.5*pi)
+                z front (yaw=-0.5*pi)
                /
               /
              0 ------> x right (yaw=0)
@@ -24,9 +24,12 @@ class CameraInstance3DBoxes(BaseInstance3DBoxes):
 
     The relative coordinate of bottom center in a CAM box is (0.5, 1.0, 0.5),
     and the yaw is around the y axis, thus the rotation axis=1.
-    The yaw is 0 at the positive direction of x axis, and increases from
+    The yaw is 0 at the positive direction of x axis, and decreases from
     the positive direction of x to the positive direction of z.
 
+    A refactor is ongoing to make the three coordinate systems
+    easier to understand and convert between each other.
+
     Attributes:
         tensor (torch.Tensor): Float matrix of N x box_dim.
         box_dim (int): Integer indicates the dimension of a box

mmdet3d/core/bbox/structures/depth_box3d.py

@@ -14,7 +14,7 @@ class DepthInstance3DBoxes(BaseInstance3DBoxes):
 
     .. code-block:: none
 
-                    up z    y front (yaw=0.5*pi)
+                    up z    y front (yaw=-0.5*pi)
                        ^   ^
                        |  /
                        | /
@@ -22,8 +22,13 @@ class DepthInstance3DBoxes(BaseInstance3DBoxes):
 
     The relative coordinate of bottom center in a Depth box is (0.5, 0.5, 0),
     and the yaw is around the z axis, thus the rotation axis=2.
-    The yaw is 0 at the positive direction of x axis, and increases from
+    The yaw is 0 at the positive direction of x axis, and decreases from
     the positive direction of x to the positive direction of y.
+    Also note that rotation of DepthInstance3DBoxes is counterclockwise,
+    which is reverse to the definition of the yaw angle (clockwise).
+
+    A refactor is ongoing to make the three coordinate systems
+    easier to understand and convert between each other.
 
     Attributes:
         tensor (torch.Tensor): Float matrix of N x box_dim.

mmdet3d/core/bbox/structures/lidar_box3d.py

@@ -14,17 +14,20 @@ class LiDARInstance3DBoxes(BaseInstance3DBoxes):
 
     .. code-block:: none
 
-                            up z    x front (yaw=0.5*pi)
+                            up z    x front (yaw=-0.5*pi)
                                ^   ^
                                |  /
                                | /
-       (yaw=pi) left y <------ 0
+      (yaw=-pi) left y <------ 0 -------- (yaw=0)
 
     The relative coordinate of bottom center in a LiDAR box is (0.5, 0.5, 0),
     and the yaw is around the z axis, thus the rotation axis=2.
-    The yaw is 0 at the negative direction of y axis, and increases from
+    The yaw is 0 at the negative direction of y axis, and decreases from
     the negative direction of y to the positive direction of x.
 
+    A refactor is ongoing to make the three coordinate systems
+    easier to understand and convert between each other.
+
     Attributes:
         tensor (torch.Tensor): Float matrix of N x box_dim.
         box_dim (int): Integer indicating the dimension of a box.