void getFOVangle(ref double fovh, ref double fovv)
{
double focallen = (double)NUM_focallength.Value;
double sensorwidth = double.Parse(TXT_senswidth.Text);
double sensorheight = double.Parse(TXT_sensheight.Text);
fovh = (float)(Math.Atan(sensorwidth / (2 * focallen)) * rad2deg * 2);
fovv = (float)(Math.Atan(sensorheight / (2 * focallen)) * rad2deg * 2);
}