Function S2Loop.getTurningAngle

Returns the sum of the turning angles at each vertex. The return value is positive if the loop is counter-clockwise, negative if the loop is clockwise, and zero if the loop is a great circle. Degenerate and nearly-degenerate loops are handled consistently with s2pred::Sign(). So for example, if a loop has zero area (i.e., it is a very small CCW loop) then the turning angle will always be negative.

This quantity is also called the "geodesic curvature" of the loop.