testbed/matplotlib__matplotlib/lib/matplotlib/projections/__init__.py

"""
Non-separable transforms that map from data space to screen space.

Projections are defined as `~.axes.Axes` subclasses.  They include the
following elements:

- A transformation from data coordinates into display coordinates.

- An inverse of that transformation.  This is used, for example, to convert
  mouse positions from screen space back into data space.

- Transformations for the gridlines, ticks and ticklabels.  Custom projections
  will often need to place these elements in special locations, and Matplotlib
  has a facility to help with doing so.

- Setting up default values (overriding `~.axes.Axes.cla`), since the defaults
  for a rectilinear axes may not be appropriate.

- Defining the shape of the axes, for example, an elliptical axes, that will be
  used to draw the background of the plot and for clipping any data elements.

- Defining custom locators and formatters for the projection.  For example, in
  a geographic projection, it may be more convenient to display the grid in
  degrees, even if the data is in radians.

- Set up interactive panning and zooming.  This is left as an "advanced"
  feature left to the reader, but there is an example of this for polar plots
  in `matplotlib.projections.polar`.

- Any additional methods for additional convenience or features.

Once the projection axes is defined, it can be used in one of two ways:

- By defining the class attribute ``name``, the projection axes can be
  registered with `matplotlib.projections.register_projection` and subsequently
  simply invoked by name::

      fig.add_subplot(projection="my_proj_name")

- For more complex, parameterisable projections, a generic "projection" object
  may be defined which includes the method ``_as_mpl_axes``. ``_as_mpl_axes``
  should take no arguments and return the projection's axes subclass and a
  dictionary of additional arguments to pass to the subclass' ``__init__``
  method.  Subsequently a parameterised projection can be initialised with::

      fig.add_subplot(projection=MyProjection(param1=param1_value))

  where MyProjection is an object which implements a ``_as_mpl_axes`` method.

A full-fledged and heavily annotated example is in
:doc:`/gallery/misc/custom_projection`.  The polar plot functionality in
`matplotlib.projections.polar` may also be of interest.
"""

from .. import axes, _docstring
from .geo import AitoffAxes, HammerAxes, LambertAxes, MollweideAxes
from .polar import PolarAxes
from mpl_toolkits.mplot3d import Axes3D


class ProjectionRegistry:
    """A mapping of registered projection names to projection classes."""

    def __init__(self):
        self._all_projection_types = {}

    def register(self, *projections):
        """Register a new set of projections."""
        for projection in projections:
            name = projection.name
            self._all_projection_types[name] = projection

    def get_projection_class(self, name):
        """Get a projection class from its *name*."""
        return self._all_projection_types[name]

    def get_projection_names(self):
        """Return the names of all projections currently registered."""
        return sorted(self._all_projection_types)


projection_registry = ProjectionRegistry()
projection_registry.register(
    axes.Axes,
    PolarAxes,
    AitoffAxes,
    HammerAxes,
    LambertAxes,
    MollweideAxes,
    Axes3D,
)


def register_projection(cls):
    projection_registry.register(cls)


def get_projection_class(projection=None):
    """
    Get a projection class from its name.

    If *projection* is None, a standard rectilinear projection is returned.
    """
    if projection is None:
        projection = 'rectilinear'

    try:
        return projection_registry.get_projection_class(projection)
    except KeyError as err:
        raise ValueError("Unknown projection %r" % projection) from err


get_projection_names = projection_registry.get_projection_names
_docstring.interpd.update(projection_names=get_projection_names())