/// <summary>
/// Get WCS at any pixel in the image
/// </summary>
/// <param name="crpix1">pixel coord 1 (double)</param>
/// <param name="crpix2">pixel coord 2 (double)</param>
/// <returns>WCS</returns>
public WCS Wcs(double crpix1, double crpix2)
{
SdssCoord[] corner;
center = CoordsAtPix(crpix1, crpix2);
corner = CornerCoords();
double mu, nu, ra, dec;
// build linear eqns and solve for affine transform
double mumu = 0, nunu = 0, munu = 0, ramu = 0, ranu = 0, decmu = 0, decnu = 0;
for (int i = 0; i < corner.Length; i++)
{
mu = corner[i].mu - center.mu;
nu = corner[i].nu - center.nu;
ra = corner[i].ra - center.ra;
dec = corner[i].dec - center.dec;
// increment
mumu += mu * mu;
munu += mu * nu;
nunu += nu * nu;
ramu += ra * mu;
ranu += ra * nu;
decmu += dec * mu;
decnu += dec * nu;
}
double p, q, s, r;
SolveSym2D(mumu, munu, nunu, ramu, ranu, out p, out q);
SolveSym2D(mumu, munu, nunu, decmu, decnu, out s, out r);
WCS wcs = new WCS();
wcs.EPOCH = "J2000";
wcs.CTYPE2 = "DEC--TAN";
wcs.CTYPE1 = "RA---TAN";
wcs.CUNIT1 = "deg";
wcs.CUNIT2 = "deg";
wcs.NAXIS1 = this.npix1;
wcs.NAXIS2 = this.npix2;
wcs.CRPIX1 = crpix1 + 0.5; // different SDSS vs FITS convention (Steve Kent)
wcs.CRPIX2 = crpix2 + 0.5; // -"-
wcs.CRVAL1 = center.ra;
wcs.CRVAL2 = center.dec;
wcs.CD1_1 = p * b + q * e;
wcs.CD1_2 = s * b + r * e;
wcs.CD2_1 = p * c + q * f;
wcs.CD2_2 = s * c + r * f;
// john's suggestions for a fix
double scale = Math.Cos(center.dec * Math.PI / 180);
wcs.CD1_1 *= scale;
wcs.CD1_2 *= scale;
return(wcs);
}
/// <summary>
/// Get the corners of the frame
/// </summary>
/// <returns>list of corner coords (SdssCoord[])</returns>
public SdssCoord[] CornerCoords()
{
SdssCoord[] corner = new SdssCoord[4];
int n = 0;
for (int i = 0; i < 2; i++)
{
for (int j = 0; j < 2; j++)
{
corner[n++] = CoordsAtMuNu(a + i * (npix1 * c + npix2 * b), d + j * (npix1 * f + npix2 * e));
}
}
return(corner);
}