private static S2LatLngRect getEdgeBound(double x1,
                                          double y1,
                                          double z1,
                                          double x2,
                                          double y2,
                                          double z2)
 {
     return(S2LatLngRect.FromEdge(
                S2Point.Normalize(new S2Point(x1, y1, z1)), S2Point.Normalize(new S2Point(x2, y2, z2))));
 }