TransformGraph¶

class
astropy.coordinates.
TransformGraph
[source]¶ Bases:
object
A graph representing the paths between coordinate frames.
Attributes Summary
A
dict
of all the attributes of all frame classes in thisTransformGraph
.A
set
of all component names every defined within any frame class in thisTransformGraph
.A
set
of all the frame classes present in thisTransformGraph
.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.
Returns all available transform names.
get_transform
(fromsys, tosys)Generates and returns the
CompositeTransform
for a transformation between two coordinate systems.Context manager to impose a finitedifference time step on all applicable transformations
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.
Converts this transform graph into a networkx graph.
transform
(transcls, fromsys, tosys[, priority])A function decorator for defining transformations.
Attributes Documentation

frame_attributes
¶ A
dict
of all the attributes of all frame classes in thisTransformGraph
.

frame_component_names
¶ A
set
of all component names every defined within any frame class in thisTransformGraph
.

frame_set
¶ A
set
of all the frame classes present in thisTransformGraph
.
Methods Documentation

add_transform
(fromsys, tosys, transform)[source]¶ Add a new coordinate transformation to the graph.
 Parameters
 fromsysclass
The coordinate frame class to start from.
 tosysclass
The coordinate frame class to transform into.
 transformCoordinateTransform 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
ortosys
are not classes ortransform
is not callable.

find_shortest_path
(fromsys, tosys)[source]¶ Computes the shortest distance along the transform graph from one system to another.
 Parameters
 fromsysclass
The coordinate frame class to start from.
 tosysclass
The coordinate frame class to transform into.
 Returns
 pathlist of classes or
None
The path from
fromsys
totosys
as an inorder sequence of classes. This list includes bothfromsys
andtosys
. IsNone
if there is no possible path. distancenumber
The total distance/priority from
fromsys
totosys
. If priorities are not set this is the number of transforms needed. Isinf
if there is no possible path.
 pathlist of classes or

get_names
()[source]¶ Returns all available transform names. They will all be valid arguments to
lookup_name
. Returns
 nmslist
The aliases for coordinate systems.

get_transform
(fromsys, tosys)[source]¶ Generates and returns the
CompositeTransform
for a transformation between two coordinate systems. Parameters
 fromsysclass
The coordinate frame class to start from.
 tosysclass
The coordinate frame class to transform into.
 Returns
 trans
CompositeTransform
orNone
If there is a path from
fromsys
totosys
, this is a transform object for that path. If no path could be found, this isNone
.
 trans
Notes
This function always returns a
CompositeTransform
, becauseCompositeTransform
is slightly more adaptable in the way it can be called than other transform classes. Specifically, it takes care of intermediate steps of transformations in a way that is consistent with 1hop transformations.

impose_finite_difference_dt
(dt)[source]¶ Context manager to impose a finitedifference time step on all applicable transformations
For each transformation in this transformation graph that has the attribute
finite_difference_dt
, that attribute is set to the provided value. The only standard transformation with this attribute isFunctionTransformWithFiniteDifference
. Parameters
 dt
Quantity
or callable If a quantity, this is the size of the differential used to do the finite difference. If a callable, should accept
(fromcoord, toframe)
and return thedt
value.
 dt

invalidate_cache
()[source]¶ 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)[source]¶ Tries to locate the coordinate class with the provided alias.
 Parameters
 namestr
The alias to look up.
 Returns
 coordcls
The coordinate class corresponding to the
name
orNone
if no such class exists.

remove_transform
(fromsys, tosys, transform)[source]¶ Removes a coordinate transform from the graph.
 Parameters
 fromsysclass or
None
The coordinate frame class to start from. If
None
,transform
will be searched for and removed (tosys
must also beNone
). tosysclass or
None
The coordinate frame class to transform into. If
None
,transform
will be searched for and removed (fromsys
must also beNone
). transformcallable or
None
The transformation object to be removed or
None
. IfNone
andtosys
andfromsys
are supplied, there will be no check to ensure the correct object is removed.
 fromsysclass or

to_dot_graph
(priorities=True, addnodes=[], savefn=None, savelayout='plain', saveformat=None, color_edges=True)[source]¶ Converts this transform graph to the graphviz DOT format.
Optionally saves it (requires graphviz be installed and on your path).
 Parameters
 prioritiesbool
If
True
, show the priority values for each transform. Otherwise, the will not be included in the graph. addnodessequence 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. savelayoutstr
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
isNone
. saveformatstr
The graphviz output format. (e.g. the
Txxx
option for the command line program  see graphviz docs for details). Ignored ifsavefn
isNone
. color_edgesbool
Color the edges between two nodes (frames) based on the type of transform.
FunctionTransform
: red,StaticMatrixTransform
: blue,DynamicMatrixTransform
: green.
 Returns
 dotgraphstr
A string with the DOT format graph.

to_networkx_graph
()[source]¶ Converts this transform graph into a networkx graph.
Note
You must have the networkx package installed for this to work.
 Returns
 nxgraphnetworkx.Graph
This
TransformGraph
as a networkx.Graph.

transform
(transcls, fromsys, tosys, priority=1, **kwargs)[source]¶ A function decorator for defining transformations.
Note
If decorating a static method of a class,
@staticmethod
should be added above this decorator. Parameters
 transclsclass
The class of the transformation object to create.
 fromsysclass
The coordinate frame class to start from.
 tosysclass
The coordinate frame class to transform into.
 prioritynumber
The priority if this transform when finding the shortest coordinate transform path  large numbers are lower priorities.
 Additional keyword arguments are passed into the ``transcls``
 constructor.
 Returns
 decofunction
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 arefromsys
andtosys
. If this is not true, you should just initialize the class manually and useadd_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
