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Avoid dividing by zero for identity axis-angle rotations #571

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Avoid dividing by zero for identity axis-angle rotations #571

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6 changes: 4 additions & 2 deletions dm_control/utils/transformations.py
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Original file line number Diff line number Diff line change
Expand Up @@ -639,8 +639,10 @@ def axisangle_to_quat(axisangle, tol=0.0):
"""
axisangle = np.asarray(axisangle)
angle = np.linalg.norm(axisangle, axis=-1, keepdims=True)
axis = np.where(angle <= tol, [1.0, 0.0, 0.0], axisangle / angle)
angle = np.where(angle <= tol, [0.0], angle)
is_identity = angle <= tol
safe_angle = np.where(is_identity, 1.0, angle)
axis = np.where(is_identity, [1.0, 0.0, 0.0], axisangle / safe_angle)
angle = np.where(is_identity, [0.0], angle)
sine, cosine = np.sin(angle / 2), np.cos(angle / 2)
return np.concatenate([cosine, axis * sine], axis=-1)

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9 changes: 6 additions & 3 deletions dm_control/utils/transformations_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -268,7 +268,8 @@ def test_axisangle_to_quat(self):

def test_axisangle_to_quat_zero(self):
axisangle = np.array([0, 0, 0])
quat = transformations.axisangle_to_quat(axisangle)
with np.errstate(invalid='raise', divide='raise'):
quat = transformations.axisangle_to_quat(axisangle)
np.testing.assert_allclose(quat, [1, 0, 0, 0])

def test_axisangle_to_quat_zero_tol(self):
Expand All @@ -277,12 +278,14 @@ def test_axisangle_to_quat_zero_tol(self):
np.testing.assert_allclose(quat, [1, 0, 0, 0])

def test_axisangle_to_quat_batched(self):
axisangle = np.stack([np.array([0.1, 0.2, 0.3]), np.array([0.4, 0.5, 0.6])])
quat = transformations.axisangle_to_quat(axisangle)
axisangle = np.array([[0.1, 0.2, 0.3], [0, 0, 0], [0.4, 0.5, 0.6]])
with np.errstate(invalid='raise', divide='raise'):
quat = transformations.axisangle_to_quat(axisangle)
np.testing.assert_allclose(
quat,
[
[0.982551, 0.0497088, 0.0994177, 0.1491265],
[1, 0, 0, 0],
[0.9052841, 0.1936448, 0.242056, 0.2904672],
],
atol=1e-6,
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