public HealpixPos Ang2Xy(double phi, double theta)
{
// longitude, latitude radians
var result = new HealpixPos();
var omega = K % 2 == 1 || theta > 0 ? 1 : 0;
if (Math.Abs(theta) > Thetax)
{
// polar
var sign = theta > 0 ? -1 : 1;
var sigma = Math.Sqrt(K * (1 - Math.Abs(Math.Sin(theta))));
var phic = -Math.PI
+ (2 * Math.Floor((phi + Math.PI) * H / (2 * Math.PI) + (1d - omega) / 2) + omega) * Math.PI /
H;
result.X = phic + (phi - phic) * sigma;
result.Y = sign * Math.PI / H * ((K + 1d) / 2 - sigma);
}
else
{
// equatorial
result.X = phi;
result.Y = K * Math.PI / (2 * H) * Math.Sin(theta);
}
return(result);
}
public Coor Xy2Ang(HealpixPos healPos)
{
var result = new Coor();
if (Math.Abs(healPos.Y) > Math.PI / 2 * (K - 1) / H)
{
// polar
var sign = healPos.Y > 0 ? 1 : -1;
var sigma = (K + 1d) / 2 - Math.Abs(healPos.Y * H) / Math.PI;
result.Beta = sign * Math.Asin(1 - sigma * sigma / K);
var omega = K % 2 == 1 || result.Beta > 0 ? 1 : 0;
var xc = -Math.PI +
(2 * Math.Floor((healPos.X + Math.PI) * H / (2 * Math.PI) + (1d - omega) / 2) + omega) *
Math.PI / H;
result.Lambda = xc + (healPos.X - xc) / sigma;
}
else
{
// equatorial
result.Lambda = healPos.X;
result.Beta = Math.Asin(healPos.Y * H * 2 / (Math.PI * K));
}
return(result);
}
