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;