Method inCircleExact

Slow exact in-circle test. Returns a positive value if the point pd lies inside the circle passing through pa, pb, and pc; a negative value if it lies outside; and zero if the four points are cocircular. The points pa, pb, and pc must be in counterclockwise order, or the sign of the result will be r

(
    double xa, double ya,
    double xb, double yb,
    double xc, double yc,
    double xd, double yd)