code: public double getSpatproduct(Vector3d a, Vector3d b, Vector3d c) {
          return (c.x * (b.y * a.z - b.z * a.y) + c.y * (b.z * a.x - b.x * a.z) + c.z * (b.x * a.y - b.y * a.x));
      }
docs: Gets the spatproduct of three vectors.
  
  @param  a  vector a
  @param  b  vector b
  @param  c  vector c
  @return    double value of the spatproduct