code: def signed_area(ring):
      """Return the signed area enclosed by a ring in linear time using the
      algorithm at: https://web.archive.org/web/20080209143651/http://cgafaq.info:80/wiki/Polygon_Area
      """
      coords = np.array(ring.coords)[:, :2]
      xs, ys = np.vstack([coords, coords[1]]).T
      return np.sum(xs[1:-1] * (ys[2:] - ys[:-2])) / 2.0
  
label_desc: Use image node_id 1 for calling a global function with example usage: signed_area(ring) and returns: unknown