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import numpy as np
from menpo.shape import PointCloud
from menpo.transform import HomogeneousTransform
If you know the form of a basic homogeneous transform (like here a mirror along y=x) it's trivial to build a HomogeneousTransform to use this operation in Menpo
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# mirror along y=x
xy_yx = HomogeneousTransform(np.array([[0, 1, 0],
[1, 0, 0],
[0, 0, 1]]))
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pc = PointCloud(np.random.random([12, 2]))
print pc
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%matplotlib inline
pc.view()
Applying this Transform to a PointCloud has the desired effect
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pc_flipped = xy_yx.apply(pc)
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pc_flipped.view()
Homogeneous transforms support native composition
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no_op = xy_yx.compose_before(xy_yx)
print no_op.h_matrix
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no_op = xy_yx.compose_after(xy_yx)
print no_op.h_matrix
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xy_yx.compose_before_inplace(xy_yx)
print xy_yx.h_matrix