http://scikit-image.org/docs/dev/api/skimage.transform.html#skimage.transform.SimilarityTransform
https://github.com/scikit-image/scikit-image/blob/master/skimage/transform/_geometric.py#L1040
https://blog.csdn.net/u014096352/article/details/53526747
2D similarity transformation.
Has the following form:
X = a0 * x - b0 * y + a1 = = s * x * cos(rotation) - s * y * sin(rotation) + a1 Y = b0 * x + a0 * y + b1 = = s * x * sin(rotation) + s * y * cos(rotation) + b1
where s is a scale factor and the homogeneous transformation matrix is:
[[a0 b0 a1] [b0 a0 b1] [0 0 1]]
The similarity transformation extends the Euclidean transformation with a single scaling factor in addition to the rotation and translation parameters.