Determines if a point d is left of the plane defined by the points a, b, and c. The latter are assumed to be in CCW order, as viewed from the right side of the plane. @param xa x coordinate of point a. @param ya y coordinate of point a. @param za z coordinate of point a. @param xb x coordinate of po
(
double xa, double ya, double za,
double xb, double yb, double zb,
double xc, double yc, double zc,
double xd, double yd, double zd)
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