public static double Atan2d(double y, double x)
{
// In order to minimize round-off errors, this function rearranges the
// arguments so that result of atan2 is in the range [-pi/4, pi/4] before
// converting it to degrees and mapping the result to the correct
// quadrant.
int q = 0;
if (Math.Abs(y) > Math.Abs(x))
{
double t; t = x; x = y; y = t; q = 2;
}
if (x < 0)
{
x = -x; ++q;
}
// here x >= 0 and x >= abs(y), so angle is in [-pi/4, pi/4]
double ang = GeoMath.ToDegrees(Math.Atan2(y, x));
switch (q)
{
// Note that atan2d(-0.0, 1.0) will return -0. However, we expect that
// atan2d will not be called with y = -0. If need be, include
//
// case 0: ang = 0 + ang; break;
//
// and handle mpfr as in AngRound.
case 1: ang = (y >= 0 ? 180 : -180) - ang; break;
case 2: ang = 90 - ang; break;
case 3: ang = -90 + ang; break;
}
return(ang);
}