TransformGraph

class astropy.coordinates.TransformGraph

Bases: object

A graph representing the paths between coordinate frames.

Attributes Summary

frame_set

A set of all the frame classes present in this TransformGraph.

Methods Summary

add_transform(fromsys, tosys, transform)	Add a new coordinate transformation to the graph.
find_shortest_path(fromsys, tosys)	Computes the shortest distance along the transform graph from one system to another.
get_names()	Returns all available transform names.
get_transform(fromsys, tosys)	Generates and returns the CompositeTransform for a transformation between two coordinate systems.
invalidate_cache()	Invalidates the cache that stores optimizations for traversing the transform graph.
lookup_name(name)	Tries to locate the coordinate class with the provided alias.
remove_transform(fromsys, tosys, transform)	Removes a coordinate transform from the graph.
to_dot_graph([priorities, addnodes, savefn, ...])	Converts this transform graph to the graphviz DOT format.
to_networkx_graph()	Converts this transform graph into a networkx graph.
transform(transcls, fromsys, tosys[, priority])	A function decorator for defining transformations.

Attributes Documentation

frame_set

A set of all the frame classes present in this TransformGraph.

Methods Documentation

add_transform(fromsys, tosys, transform)

Add a new coordinate transformation to the graph.

Parameters:

fromsys : class

The coordinate frame class to start from.

tosys : class

The coordinate frame class to transform into.

transform : CoordinateTransform or similar callable

The transformation object. Typically a CoordinateTransform object, although it may be some other callable that is called with the same signature.

Raises:

TypeError

If fromsys or tosys are not classes or transform is not callable.

find_shortest_path(fromsys, tosys)

Computes the shortest distance along the transform graph from one system to another.

Parameters:

fromsys : class

The coordinate frame class to start from.

tosys : class

The coordinate frame class to transform into.

Returns:

path : list of classes or None

The path from fromsys to tosys as an in-order sequence of classes. This list includes both fromsys and tosys. Is None if there is no possible path.

distance : number

The total distance/priority from fromsys to tosys. If priorities are not set this is the number of transforms needed. Is inf if there is no possible path.

get_names()

Returns all available transform names. They will all be valid arguments to lookup_name.

Returns:

nms : list

The aliases for coordinate systems.

get_transform(fromsys, tosys)

Generates and returns the CompositeTransform for a transformation between two coordinate systems.

Parameters:

fromsys : class

The coordinate frame class to start from.

tosys : class

The coordinate frame class to transform into.

Returns:

trans : CompositeTransform or None

If there is a path from fromsys to tosys, this is a transform object for that path. If no path could be found, this is None.

Notes

This function always returns a CompositeTransform, because CompositeTransform is slightly more adaptable in the way it can be called than other transform classes. Specifically, it takes care of inetermediate steps of transformations in a way that is consistent with 1-hop transformations.

invalidate_cache()

Invalidates the cache that stores optimizations for traversing the transform graph. This is called automatically when transforms are added or removed, but will need to be called manually if weights on transforms are modified inplace.

lookup_name(name)

Tries to locate the coordinate class with the provided alias.

Parameters:

name : str

The alias to look up.

Returns:

coordcls

The coordinate class corresponding to the name or None if no such class exists.

remove_transform(fromsys, tosys, transform)

Removes a coordinate transform from the graph.

Parameters:

fromsys : class or None

The coordinate frame class to start from. If None, transform will be searched for and removed (tosys must also be None).

tosys : class or None

The coordinate frame class to transform into. If None, transform will be searched for and removed (fromsys must also be None).

transform : callable or None

The transformation object to be removed or None. If None and tosys and fromsys are supplied, there will be no check to ensure the correct object is removed.

to_dot_graph(priorities=True, addnodes=, []savefn=None, savelayout=u'plain', saveformat=None)

Converts this transform graph to the graphviz DOT format.

Optionally saves it (requires graphviz be installed and on your path).

Parameters:

priorities : bool

If True, show the priority values for each transform. Otherwise, the will not be included in the graph.

addnodes : sequence of str

Additional coordinate systems to add (this can include systems already in the transform graph, but they will only appear once).

savefn : None or str

The file name to save this graph to or None to not save to a file.

savelayout : str

The graphviz program to use to layout the graph (see graphviz for details) or ‘plain’ to just save the DOT graph content. Ignored if savefn is None.

saveformat : str

The graphviz output format. (e.g. the -Txxx option for the command line program - see graphviz docs for details). Ignored if savefn is None.

Returns:

dotgraph : str

A string with the DOT format graph.

to_networkx_graph()

Converts this transform graph into a networkx graph.

Note

You must have the networkx package installed for this to work.

Returns:

nxgraph : networkx.Graph

This TransformGraph as a networkx.Graph.

transform(transcls, fromsys, tosys, priority=1)

A function decorator for defining transformations.

Note

If decorating a static method of a class, @staticmethod should be added above this decorator.

Parameters:

transcls : class

The class of the transformation object to create.

fromsys : class

The coordinate frame class to start from.

tosys : class

The coordinate frame class to transform into.

priority : number

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

Returns:

deco : function

A function that can be called on another function as a decorator (see example).

Notes

This decorator assumes the first argument of the transcls initializer accepts a callable, and that the second and third are fromsys and tosys. If this is not true, you should just initialize the class manually and use add_transform instead of using this decorator.

Examples

graph = TransformGraph()

class Frame1(BaseCoordinateFrame):
   ...

class Frame2(BaseCoordinateFrame):
    ...

@graph.transform(FunctionTransform, Frame1, Frame2)
def f1_to_f2(f1_obj):
    ... do something with f1_obj ...
    return f2_obj