class astropy.coordinates.BaseAffineTransform(fromsys, tosys, priority=1, register_graph=None)[source]

Bases: astropy.coordinates.CoordinateTransform

Base class for common functionality between the AffineTransform-type subclasses.

This base class is needed because AffineTransform and the matrix transform classes share the _apply_transform() method, but have different __call__() methods. StaticMatrixTransform passes in a matrix stored as a class attribute, and both of the matrix transforms pass in None for the offset. Hence, user subclasses would likely want to subclass this (rather than AffineTransform) if they want to provide alternative transformations using this machinery.