Split out conversion from CircleSkyRegion to PolygonSkyRegion

regions/core/core.py

@@ -284,6 +284,17 @@ def area(self):
         Returns the area of the region as a `~astropy.units.Quantity`.
         """
 
+    @abc.abstractmethod
+    def to_polygon(self, points=100):
+        """
+        Convert the region to a polygon.
+
+        Parameters
+        ----------
+        points : int, optional
+            Number of points in the final polygon.
+        """
+
     @abc.abstractmethod
     def to_pixel(self, wcs, mode='local', tolerance=None):
         """

regions/shapes/circle.py

@@ -7,11 +7,11 @@
 
 from astropy import units as u
 from astropy.coordinates import Angle, SkyCoord
-from astropy.wcs.utils import pixel_to_skycoord, skycoord_to_pixel
+from astropy.wcs.utils import pixel_to_skycoord
 
-from .polygon import PolygonPixelRegion
+from .polygon import PolygonSkyRegion
 
-from ..core import PixelRegion, SkyRegion, Mask, BoundingBox, PixCoord
+from ..core import PixelRegion, SkyRegion, Mask, BoundingBox
 from .._utils.wcs_helpers import skycoord_to_pixel_scale_angle
 from .._geometry import circular_overlap_grid, rotate_polygon
 
@@ -158,6 +158,28 @@ def area(self):
     def contains(self, skycoord):
         return self.center.separation(skycoord) < self.radius
 
+    def to_polygon(self, points=100):
+
+        # TODO: avoid converting to unit spherical or spherical if already
+        #       using a spherical representation
+
+        # Extract longitude/latitude, either from a tuple of two quantities, or
+        # a single 2-element Quantity.
+        rep = self.center.represent_as('unitspherical')
+        longitude, latitude = rep.lon, rep.lat
+
+        # Start off by generating the circle around the North pole
+        lon = np.linspace(0., 2 * np.pi, points + 1)[:-1] * u.radian
+        lat = np.repeat(0.5 * np.pi - self.radius.to(u.radian).value, points) * u.radian
+
+        # Now rotate it to the correct longitude/latitude
+        lon, lat = rotate_polygon(lon, lat, longitude, latitude)
+
+        # Make a new SkyCoord
+        vertices_sky = SkyCoord(lon, lat, frame=self.center)
+
+        return PolygonSkyRegion(vertices_sky)
+
     def to_pixel(self, wcs, mode='local', tolerance=100):
         """
         Given a WCS, convert the circle to a best-approximation circle in pixel
@@ -187,30 +209,7 @@ def to_pixel(self, wcs, mode='local', tolerance=100):
 
         elif mode == 'full':
 
-            # TODO: avoid converting to unit spherical or spherical if already
-            #       using a spherical representation
-
-            # Extract longitude/latitude, either from a tuple of two quantities, or
-            # a single 2-element Quantity.
-            rep = self.center.represent_as('unitspherical')
-            longitude, latitude = rep.lon, rep.lat
-
-            # Start off by generating the circle around the North pole
-            lon = np.linspace(0., 2 * np.pi, tolerance + 1)[:-1] * u.radian
-            lat = np.repeat(0.5 * np.pi - self.radius.to(u.radian).value, tolerance) * u.radian
-
-            # Now rotate it to the correct longitude/latitude
-            lon, lat = rotate_polygon(lon, lat, longitude, latitude)
-
-            # Make a new SkyCoord
-            vertices_sky = SkyCoord(lon, lat, frame=self.center)
-
-            # Convert to PixCoord
-            x, y = skycoord_to_pixel(vertices_sky, wcs)
-            vertices_pix = PixCoord(x, y)
-
-            # Make polygon
-            return PolygonPixelRegion(vertices_pix)
+            return self.to_polygon(points=tolerance).to_pixel(wcs)
 
         else:
             raise ValueError('mode should be one of local/affine/full')

regions/shapes/ellipse.py

@@ -196,6 +196,10 @@ def contains(self, skycoord):
         # TODO: needs to be implemented
         raise NotImplementedError
 
+    def to_polygon(self, points=100):
+        # TODO: needs to be implemented
+        raise NotImplementedError
+
     def to_pixel(self, wcs, mode='local', tolerance=None):
         # TODO: needs to be implemented
         raise NotImplementedError

regions/shapes/point.py

@@ -88,6 +88,10 @@ def area(self):
     def contains(self, skycoord):
         return False
 
+    def to_polygon(self, points=100):
+        # TODO: needs to be implemented
+        raise NotImplementedError
+
     def to_pixel(self, wcs, mode='local', tolerance=None):
         # TODO: needs to be implemented
         raise NotImplementedError

regions/shapes/polygon.py

@@ -4,7 +4,9 @@
 
 import numpy as np
 
-from ..core import PixelRegion, SkyRegion, Mask, BoundingBox
+from astropy.wcs.utils import skycoord_to_pixel
+
+from ..core import PixelRegion, SkyRegion, Mask, BoundingBox, PixCoord
 from .._geometry import polygonal_overlap_grid
 from .._geometry.pnpoly import points_in_polygon
 
@@ -140,6 +142,16 @@ def contains(self, skycoord):
         # TODO: needs to be implemented
         raise NotImplementedError
 
-    def to_pixel(self, wcs, mode='local', tolerance=None):
-        # TODO: needs to be implemented
+    def to_polygon(self, points=100):
+        # TODO: decide how this should behave. Return self?
         raise NotImplementedError
+
+    def to_pixel(self, wcs, mode='local', tolerance=None):
+
+        if mode == 'local':
+            x, y = skycoord_to_pixel(self.vertices, wcs)
+            vertices_pix = PixCoord(x, y)
+            return PolygonPixelRegion(vertices_pix)
+        else:
+
+            raise NotImplementedError()

regions/shapes/rectangle.py

@@ -215,6 +215,10 @@ def contains(self, skycoord):
         # TODO: needs to be implemented
         raise NotImplementedError
 
+    def to_polygon(self, points=100):
+        # TODO: needs to be implemented
+        raise NotImplementedError
+
     def to_pixel(self, wcs, mode='local', tolerance=None):
         # TODO: needs to be implemented
         raise NotImplementedError