16 const double PI = 3.141592653589793238462643383279502884;
17 const double PI_2 = 1.570796326794896619231321691639751442;
18 const double PI_4 = 0.785398163397448309615660845819875721;
19 const double deg2rad = 0.017453292519943295769236907684886127;
20 const double rad2deg = 57.29577951308232087679815481410517033;