ccw.py

def formatPolygon(coords):
    """Accepts a set of coordinates, in sequence, and checks that they
    are formatted counter-clockwise; returns an Earth Engine polygon.

    Works for non-convex polygons."""
    def _edger(c0, c1):
        # anonymous function to generate the edge value between
        # coordinate tuples `c0` and `c1`
        x0, y0 = c0
        x1, y1 = c1
        return (x1 - x0) * (y1 + y0)

    coord_seq = range(0, len(coords)-1)
    coll = [_edger(coords[i], coords[i+1]) for i in coord_seq]

    if sum(coll) > 0:
        coords = list(reversed(coords))

    # return an Earth Engine polygon
    return ee.Feature.Polygon(coords)