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Fix rotation conversion signs at Euler singularities #555

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Fix rotation conversion signs at Euler singularities #555

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201f664
Fix rotation conversion signs at Euler singularities
YaoxinHuang Sep 20, 2026
7748464
Test rotation round trips at Tait-Bryan singularities
YaoxinHuang Sep 20, 2026
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6 changes: 3 additions & 3 deletions dm_control/utils/transformations.py
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Original file line number Diff line number Diff line change
Expand Up @@ -116,7 +116,7 @@ def _rmat_to_euler_zyx(rmat):
"""Converts a 3x3 rotation matrix to ZYX euler angles."""
if rmat[2, 0] > _POLE_LIMIT:
logging.warning('Angle at North Pole')
x = np.arctan2(rmat[0, 1], rmat[0, 2])
x = np.arctan2(-rmat[0, 1], -rmat[0, 2])
y = -np.pi/2
z = 0.0
return np.array([z, y, x])
Expand All @@ -140,7 +140,7 @@ def _rmat_to_euler_xzy(rmat):
"""Converts a 3x3 rotation matrix to XZY euler angles."""
if rmat[0, 1] > _POLE_LIMIT:
logging.warning('Angle at North Pole')
y = np.arctan2(rmat[1, 2], rmat[1, 0])
y = np.arctan2(-rmat[1, 2], -rmat[1, 0])
z = -np.pi/2
x = 0.0
return np.array([x, z, y])
Expand All @@ -164,7 +164,7 @@ def _rmat_to_euler_yzx(rmat):
"""Converts a 3x3 rotation matrix to YZX euler angles."""
if rmat[1, 0] > _POLE_LIMIT:
logging.warning('Angle at North Pole')
x = -np.arctan2(rmat[0, 2], rmat[0, 1])
x = np.arctan2(rmat[0, 2], -rmat[0, 1])
z = np.pi/2
y = 0.0
return np.array([y, z, x])
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10 changes: 10 additions & 0 deletions dm_control/utils/transformations_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -109,6 +109,16 @@ def test_euler_to_rmat_special(self, angles):
euler_angles = transformations.rmat_to_euler(r, ordering)
np.testing.assert_allclose(euler_angles, [r1, r2, r3])

@parameterized.parameters('XYZ', 'ZYX', 'XZY', 'YZX', 'ZXY', 'YXZ')
def test_rmat_to_euler_tait_bryan_singularities(self, ordering):
middle_angles = (-np.pi/2, np.pi/2)
for angles in itertools.product((-.3, .3), middle_angles, (-.7, .7)):
rmat = transformations.euler_to_rmat(angles, ordering)
euler_angles = transformations.rmat_to_euler(rmat, ordering)
# Euler angles are not unique at a singularity, but the rotation is.
reconstructed = transformations.euler_to_rmat(euler_angles, ordering)
np.testing.assert_allclose(reconstructed, rmat, atol=1e-10)

def test_quat_mul_vs_mat_mul_random(self):
for _ in range(_NUM_RANDOM_SAMPLES):
quat1 = self._random_quaternion()
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