Change polygons defined with cut lines into disjoint polygons #123
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Older versions of spherical_geometry defined disjoint polygons as a single polygon joined by cut lines. When taking the intersection or union between polygons, the first step was to remove thes cut lines. However, when two polygons have a shared edge, the edge looks like a cut line and is removed, causing an error with the intereection and union methods. This fix moves the removal of the cut lines into the initialization of a SphericalPolygon. The single polygon with cut lines is thus transformed into a list of polygons without cut lines. And the initial step of removing cut lines in the union and intersection methods can be removed, which fixes the problem of the spurious removal of the shared edge of two polygons.
The spherical geometry code has been updated to remove cut lines from polygons, but the difficult test cases bypassed the code in SphericalGeometry that implements the fix. The test has been updated to call the new code.
I had deleted a test case from difficult_intersections.txt because it was causing me problems. But as Shakespeare said, "The fault, dear Horatio, is not in the stars, but in ourselves." Changing the test case code, fixed the problem, so I have restored the test case.
As astropy no longer supports python 2.7 and spherical geometry is an astropy affiliated library, so I have removed python 2.7 test cases from the test matrix.
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Older versions of spherical_geometry defined disjoint polygons as a single polygon joined by cut lines. When taking the intersection or union between polygons, the first step was to remove thes cut lines. However, when two polygons have a shared edge, the edge looks like a cut line and is removed, causing an error with the intereection and union methods. This fix moves the removal of the cut lines into the initialization of a SphericalPolygon. The single polygon with cut lines is thus transformed into a list of polygons without cut lines. And the initial step of removing cut lines in the union and intersection methods can be removed, which fixes the problem of the spurious removal of the shared edge of two polygons.