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# AffineTransform

class astropy.coordinates.AffineTransform(transform_func, fromsys, tosys, priority=1, register_graph=None)

  Bases: `BaseAffineTransform`

  A coordinate transformation specified as a function that yields a 3 x 3 cartesian transformation matrix and a tuple of displacement vectors.

  See `Galactocentric` for an example.

  Parameters:
    transform_func `python:callable()`

      A callable that has the signature `transform_func(fromcoord, toframe)` and returns: a (3, 3) matrix that operates on `fromcoord` in a Cartesian representation, and a `CartesianRepresentation` with (optionally) an attached velocity `CartesianDifferential` to represent a translation and offset in velocity to apply after the matrix operation.

    fromsys class

      The coordinate frame class to start from.

    tosys class

      The coordinate frame class to transform into.

    priority `python:float` or `python:int`

      The priority if this transform when finding the shortest coordinate transform path - large numbers are lower priorities.

    register_graph `TransformGraph` or `python:None`

      A graph to register this transformation with on creation, or `None` to leave it unregistered.

  Raises:
    `TypeError`

      If `transform_func` is not callable