423A35C7/pytorch3d
1
0
Fork 0
mirror of https://github.com/facebookresearch/pytorch3d.git synced 2025-12-21 14:50:36 +08:00
Code Issues Packages Projects Releases Wiki Activity

matrix_to_quaternion corner case

Browse Source 
Summary: Issue #119. The function `sqrt(max(x, 0))` is not convex and has infinite gradient at 0, but 0 is a subgradient at 0. Here we implement it in such a way as to give 0 as the gradient.

Reviewed By: gkioxari

Differential Revision: D24306294

fbshipit-source-id: 48d136faca083babad4d64970be7ea522dbe9e09
This commit is contained in:
Jeremy Reizenstein
2020-10-15 03:19:51 -07:00
committed by Facebook GitHub Bot
parent 2d39723610
commit 4d52f9fb8b
2 changed files with 29 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
pytorch3d/transforms/rotation_conversions.py
View File

@@ -82,6 +82,17 @@ def _copysign(a, b):
return torch.where(signs_differ, -a, a)
def _sqrt_positive_part(x):
"""
Returns torch.sqrt(torch.max(0, x))
but with a zero subgradient where x is 0.
"""
ret = torch.zeros_like(x)
positive_mask = x > 0
ret[positive_mask] = torch.sqrt(x[positive_mask])
return ret
def matrix_to_quaternion(matrix):
"""
Convert rotations given as rotation matrices to quaternions.
@@ -94,14 +105,13 @@ def matrix_to_quaternion(matrix):
"""
if matrix.size(-1) != 3 or matrix.size(-2) != 3:
raise ValueError(f"Invalid rotation matrix shape f{matrix.shape}.")
zero = matrix.new_zeros((1,))
m00 = matrix[..., 0, 0]
m11 = matrix[..., 1, 1]
m22 = matrix[..., 2, 2]
o0 = 0.5 * torch.sqrt(torch.max(zero, 1 + m00 + m11 + m22))
x = 0.5 * torch.sqrt(torch.max(zero, 1 + m00 - m11 - m22))
y = 0.5 * torch.sqrt(torch.max(zero, 1 - m00 + m11 - m22))
z = 0.5 * torch.sqrt(torch.max(zero, 1 - m00 - m11 + m22))
o0 = 0.5 * _sqrt_positive_part(1 + m00 + m11 + m22)
x = 0.5 * _sqrt_positive_part(1 + m00 - m11 - m22)
y = 0.5 * _sqrt_positive_part(1 - m00 + m11 - m22)
z = 0.5 * _sqrt_positive_part(1 - m00 - m11 + m22)
o1 = _copysign(x, matrix[..., 2, 1] - matrix[..., 1, 2])
o2 = _copysign(y, matrix[..., 0, 2] - matrix[..., 2, 0])
o3 = _copysign(z, matrix[..., 1, 0] - matrix[..., 0, 1])