diff options
Diffstat (limited to 'stsci/sphere/graph.py')
| -rw-r--r-- | stsci/sphere/graph.py | 38 |
1 files changed, 30 insertions, 8 deletions
diff --git a/stsci/sphere/graph.py b/stsci/sphere/graph.py index bae1c60..01c582a 100644 --- a/stsci/sphere/graph.py +++ b/stsci/sphere/graph.py @@ -814,6 +814,28 @@ class Graph: else: break + @staticmethod + def _fast_area(points): + """ + Calculates an approximate area of a polygon. Unlike the area + calculation in `SphericalPolygon`, this does not interpolate + along the arcs, so is not useful for getting an actual area, + but only whether the area is positive or negative, telling us + whether the points proceed clockwise or counter-clockwise + respectively. + """ + # Rotate polygon so that center of polygon is at north pole + centroid = np.mean(points[:-1], axis=0) + centroid = vector.normalize_vector(centroid) + points = points - (centroid + np.array([0, 0, 1])) + vector.normalize_vector(points, output=points) + + XY = vector.equal_area_proj(points) + X = XY[..., 0] + Y = XY[..., 1] + + return np.sum(X[:-1] * Y[1:] - X[1:] * Y[:-1]) + def _trace(self): """ Given a graph that has had cutlines removed and all @@ -824,13 +846,7 @@ class Graph: edges = set(self._edges) # copy while len(edges): polygon = [] - # Carefully pick out an "original" edge first. Synthetic - # edges may not be pointing in the right direction to - # properly calculate the area. - for edge in edges: - if len(edge._source_polygons) == 1: - break - edges.remove(edge) + edge = edges.pop() start_node = node = edge._nodes[0] while True: # TODO: Do we need this if clause any more? @@ -846,7 +862,13 @@ class Graph: polygon.append(node._point) break - polygons.append(np.asarray(polygon)) + polygon = np.asarray(polygon) + area = self._fast_area(polygon) + if area < 0: + # Reverse the points + polygon = polygon[::-1, ...] + + polygons.append(polygon) if len(polygons) == 1: return polygons[0] |