Error in class transforms.Translate

[hfutcgncas]

🐛 Error in class pytorch3d.transforms.Translate

I suppose the “translate” part should be in the last column of matrix, not in the last row.

Instructions To Reproduce the Issue:

when I wrote the code like this:

import pytorch3d.transforms as p3d_t
t = p3d_t.Transform3d().translate(1,2,3)
print(t.get_matrix())

I got

tensor([[[1., 0., 0., 0.],
         [0., 1., 0., 0.],
         [0., 0., 1., 0.],
         [1., 2., 3., 1.]]])

while I suppose the correct response should be

tensor([[[1., 0., 0., 1.],
         [0., 1., 0., 2.],
         [0., 0., 1., 3.],
         [0., 0., 0., 1.]]])

I suppose chang the mat[:, :3, 3] to mat[:, 3, :3] in line 388 and 394 of pytorch3d.transforms would fix it.

[nikhilaravi]

@hfutcgncas this just depends on whether you are using row-major or column-major ordering. As explained in the __init__ function of the Translate class, we assume row-major ordering.

See this guide for a more detailed explanation.

[hfutcgncas]

Thank you very much for the explanation.

[hfutcgncas]

@nikhilaravi I still have a problem here. In the case of using row-major, I suppose the matrix of RotateAxisAngle(a, axis="X") should be like

m = [ [1,       0,       0,     0],
      [0,  cos(a),  sin(a),     0],
      [0, -sin(a),  cos(a),     0],
      [0,       0,       0,     1]]

but in the code of RotateAxisAngle it is write like

m = [ [1,       0,       0,     0],
      [0,  cos(a), -sin(a),     0],
      [0,  sin(a),  cos(a),     0],
      [0,       0,       0,     1]]

Is there something wrong or I got some mistake about the Coordinate Systems?

[nikhilaravi]

@hfutcgncas you're right, thanks for pointing this out. If we assume row-major ordering, a right hand coordinate system and that positive angles result in counter clockwise rotation then we need to transpose the rotation matrix as you mentioned. I will make the fix ASAP.

[nikhilaravi]

@hfutcgncas This fix has now been landed.