Add a context manager for imposing a solar-radius value

sunpy/coordinates/__init__.py

@@ -21,6 +21,7 @@
 from . import sun
 from ._transformations import _make_sunpy_graph, propagate_with_solar_surface, transform_with_sun_center
 from .ephemeris import *
+from .frameattributes import impose_solar_radius
 from .frames import *
 from .metaframes import *
 from .wcs_utils import *

sunpy/coordinates/frameattributes.py

@@ -1,12 +1,15 @@
 import datetime
+from contextlib import contextmanager
 
 import astropy.units as u
-from astropy.coordinates import BaseCoordinateFrame, CoordinateAttribute, SkyCoord, TimeAttribute
+from astropy.coordinates import BaseCoordinateFrame, CoordinateAttribute, QuantityAttribute, SkyCoord, TimeAttribute
 from astropy.time import Time
 
+from sunpy.sun.constants import radius
 from sunpy.time import parse_time
 
-__all__ = ['TimeFrameAttributeSunPy', 'ObserverCoordinateAttribute']
+__all__ = ['TimeFrameAttributeSunPy', 'ObserverCoordinateAttribute',
+           'SolarRadiusAttribute', 'impose_solar_radius']
 
 
 class TimeFrameAttributeSunPy(TimeAttribute):
@@ -155,3 +158,32 @@
                     return observer
 
         return super().__get__(instance, frame_cls=frame_cls)
+
+
+_imposed_solar_radius = None
+
+
+@contextmanager
+@u.quantity_input
+def impose_solar_radius(rsun: u.km = radius.to(u.km)):
+    try:
+        global _imposed_solar_radius
+        old_imposed_solar_radius = _imposed_solar_radius
+        _imposed_solar_radius = rsun
+        yield
+    finally:
+        _imposed_solar_radius = old_imposed_solar_radius
+
+
+class SolarRadiusAttribute(QuantityAttribute):
+    """
+    """
+    def __init__(self, *args, **kwargs):
+        new_kwargs = {'default': radius, 'unit': u.km}
+        new_kwargs.update(kwargs)
+        super().__init__(*args, **new_kwargs)
+
+    def __get__(self, instance, frame_cls=None):
+        if _imposed_solar_radius is not None:
+            return _imposed_solar_radius
+        return super().__get__(instance, frame_cls=frame_cls)

sunpy/coordinates/frames.py

@@ -27,11 +27,10 @@
 from astropy.utils.data import download_file
 
 from sunpy import log
-from sunpy.sun.constants import radius as _RSUN
 from sunpy.time.time import _variables_for_parse_time_docstring
 from sunpy.util.decorators import add_common_docstring
 from sunpy.util.exceptions import warn_user
-from .frameattributes import ObserverCoordinateAttribute, TimeFrameAttributeSunPy
+from .frameattributes import ObserverCoordinateAttribute, TimeFrameAttributeSunPy, SolarRadiusAttribute
 
 _J2000 = Time('J2000.0', scale='tt')
 
@@ -218,7 +217,7 @@ class BaseHeliographic(SunPyBaseCoordinateFrame):
                                 RepresentationMapping('d_distance', 'd_radius', u.km/u.s)],
     }
 
-    rsun = QuantityAttribute(default=_RSUN, unit=u.km)
+    rsun = SolarRadiusAttribute()
 
     def make_3d(self):
         """
@@ -531,7 +530,7 @@ class Helioprojective(SunPyBaseCoordinateFrame):
                                       RepresentationMapping('lat', 'Ty', u.arcsec)],
     }
 
-    rsun = QuantityAttribute(default=_RSUN, unit=u.km)
+    rsun = SolarRadiusAttribute()
     observer = ObserverCoordinateAttribute(HeliographicStonyhurst)
 
     @property