main/src/georegression/geometry/algs/AndrewMonotoneConvexHull_F64.java
private static double subtractThenCross( Point2D_F64 a , Point2D_F64 b , Point2D_F64 c ) {
		double x0 = b.x - a.x;
		double y0 = b.y - a.y;

		double x1 = c.x - a.x;
		double y1 = c.y - a.y;

		return x0 * y1 - y0 * x1;
	}
private static double subtractThenCross( Point2D_F64 a , Point2D_F64 b , Point2D_F64 c ) {
		double x0 = b.x - a.x;
		double y0 = b.y - a.y;

		double x1 = c.x - a.x;
		double y1 = c.y - a.y;

		return x0 * y1 - y0 * x1;
	}
Performs the following operation: output = z-component[ (a-b) cross (a-c) ]