scipy.spatial.transform.Rotation¶

class scipy.spatial.transform.Rotation(quat, normalized=False, copy=True)[source]

Rotation in 3 dimensions.

This class provides an interface to initialize from and represent rotations with:

• Quaternions
• Direction Cosine Matrices
• Rotation Vectors
• Euler angles

The following operations on rotations are supported:

• Application on vectors
• Rotation Composition
• Rotation Inversion
• Rotation Indexing

Indexing within a rotation is supported since multiple rotation transforms can be stored within a single Rotation instance.

To create Rotation objects use from_… classmethods, __init__ is not supposed to be used directly.

Examples

>>> from scipy.spatial.transform import Rotation as R


A Rotation instance can be initialized in any of the above formats and converted to any of the others. The underlying object is independent of the representation used for initialization.

Consider a counter-clockwise rotation of 90 degrees about the z-axis. This corresponds to the following quaternion (in scalar-last format):

>>> r = R.from_quat([0, 0, np.sin(np.pi/4), np.cos(np.pi/4)])


The rotation can be expressed in any of the other formats:

>>> r.as_dcm()
array([[ 2.22044605e-16, -1.00000000e+00,  0.00000000e+00],
[ 1.00000000e+00,  2.22044605e-16,  0.00000000e+00],
[ 0.00000000e+00,  0.00000000e+00,  1.00000000e+00]])
>>> r.as_rotvec()
array([0.        , 0.        , 1.57079633])
>>> r.as_euler('zyx', degrees=True)
array([90.,  0.,  0.])


The same rotation can be initialized using a direction cosine matrix:

>>> r = R.from_dcm(np.array([
... [0, -1, 0],
... [1, 0, 0],
... [0, 0, 1]]))


Representation in other formats:

>>> r.as_quat()
array([0.        , 0.        , 0.70710678, 0.70710678])
>>> r.as_rotvec()
array([0.        , 0.        , 1.57079633])
>>> r.as_euler('zyx', degrees=True)
array([90.,  0.,  0.])


The rotation vector corresponding to this rotation is given by:

>>> r = R.from_rotvec(np.pi/2 * np.array([0, 0, 1]))


Representation in other formats:

>>> r.as_quat()
array([0.        , 0.        , 0.70710678, 0.70710678])
>>> r.as_dcm()
array([[ 2.22044605e-16, -1.00000000e+00,  0.00000000e+00],
[ 1.00000000e+00,  2.22044605e-16,  0.00000000e+00],
[ 0.00000000e+00,  0.00000000e+00,  1.00000000e+00]])
>>> r.as_euler('zyx', degrees=True)
array([90.,  0.,  0.])


The from_euler function is quite flexible in the range of input formats it supports. Here we initialize a single rotation about a single axis:

>>> r = R.from_euler('z', 90, degrees=True)


Again, the object is representation independent and can be converted to any other format:

>>> r.as_quat()
array([0.        , 0.        , 0.70710678, 0.70710678])
>>> r.as_dcm()
array([[ 2.22044605e-16, -1.00000000e+00,  0.00000000e+00],
[ 1.00000000e+00,  2.22044605e-16,  0.00000000e+00],
[ 0.00000000e+00,  0.00000000e+00,  1.00000000e+00]])
>>> r.as_rotvec()
array([0.        , 0.        , 1.57079633])


It is also possible to initialize multiple rotations in a single instance using any of the from_… functions. Here we initialize a stack of 3 rotations using the from_euler function:

>>> r = R.from_euler('zyx', [
... [90, 0, 0],
... [0, 45, 0],
... [45, 60, 30]], degrees=True)


The other representations also now return a stack of 3 rotations. For example:

>>> r.as_quat()
array([[0.        , 0.        , 0.70710678, 0.70710678],
[0.        , 0.38268343, 0.        , 0.92387953],
[0.39190384, 0.36042341, 0.43967974, 0.72331741]])


Applying the above rotations onto a vector:

>>> v = [1, 2, 3]
>>> r.apply(v)
array([[-2.        ,  1.        ,  3.        ],
[ 2.82842712,  2.        ,  1.41421356],
[ 2.24452282,  0.78093109,  2.89002836]])


A Rotation instance can be indexed and sliced as if it were a single 1D array or list:

>>> r.as_quat()
array([[0.        , 0.        , 0.70710678, 0.70710678],
[0.        , 0.38268343, 0.        , 0.92387953],
[0.39190384, 0.36042341, 0.43967974, 0.72331741]])
>>> p = r[0]
>>> p.as_dcm()
array([[ 2.22044605e-16, -1.00000000e+00,  0.00000000e+00],
[ 1.00000000e+00,  2.22044605e-16,  0.00000000e+00],
[ 0.00000000e+00,  0.00000000e+00,  1.00000000e+00]])
>>> q = r[1:3]
>>> q.as_quat()
array([[0.        , 0.38268343, 0.        , 0.92387953],
[0.39190384, 0.36042341, 0.43967974, 0.72331741]])


Multiple rotations can be composed using the * operator:

>>> r1 = R.from_euler('z', 90, degrees=True)
>>> r2 = R.from_rotvec([np.pi/4, 0, 0])
>>> v = [1, 2, 3]
>>> r2.apply(r1.apply(v))
array([-2.        , -1.41421356,  2.82842712])
>>> r3 = r2 * r1 # Note the order
>>> r3.apply(v)
array([-2.        , -1.41421356,  2.82842712])


Finally, it is also possible to invert rotations:

>>> r1 = R.from_euler('z', [90, 45], degrees=True)
>>> r2 = r1.inv()
>>> r2.as_euler('zyx', degrees=True)
array([[-90.,   0.,   0.],
[-45.,   0.,   0.]])


These examples serve as an overview into the Rotation class and highlight major functionalities. For more thorough examples of the range of input and output formats supported, consult the individual method’s examples.

Methods

 __len__() Number of rotations contained in this object. from_quat(quat[, normalized]) Initialize from quaternions. from_dcm(dcm) Initialize from direction cosine matrices. from_rotvec(rotvec) Initialize from rotation vectors. from_euler(seq, angles[, degrees]) Initialize from Euler angles. as_quat() Represent as quaternions. as_dcm() Represent as direction cosine matrices. as_rotvec() Represent as rotation vectors. as_euler(seq[, degrees]) Represent as Euler angles. apply(vectors[, inverse]) Apply this rotation to a set of vectors. __mul__(other) Compose this rotation with the other. inv() Invert this rotation. __getitem__(indexer) Extract rotation(s) at given index(es) from object. random([num, random_state]) Generate uniformly distributed rotations.