/*** File saoimage/wcslib/platepos.c *** February 29, 2000 *** By Jessica Mink, jmink@cfa.harvard.edu *** Harvard-Smithsonian Center for Astrophysics *** Copyright (C) 1998-2002 *** Smithsonian Astrophysical Observatory, Cambridge, MA, USA This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Correspondence concerning WCSTools should be addressed as follows: Internet email: jmink@cfa.harvard.edu Postal address: Jessica Mink Smithsonian Astrophysical Observatory 60 Garden St. Cambridge, MA 02138 USA * Module: platepos.c (Plate solution WCS conversion * Purpose: Compute WCS from plate fit * Subroutine: platepos() converts from pixel location to RA,Dec * Subroutine: platepix() converts from RA,Dec to pixel location These functions are based on the astrmcal.c portion of GETIMAGE by J. Doggett and the documentation distributed with the Digital Sky Survey. */ #include #include #include #include "wcs.h" int platepos (xpix, ypix, wcs, xpos, ypos) /* Routine to determine accurate position for pixel coordinates */ /* returns 0 if successful otherwise 1 = angle too large for projection; */ /* based on amdpos() from getimage */ /* Input: */ double xpix; /* x pixel number (RA or long without rotation) */ double ypix; /* y pixel number (dec or lat without rotation) */ struct WorldCoor *wcs; /* WCS parameter structure */ /* Output: */ double *xpos; /* Right ascension or longitude in degrees */ double *ypos; /* Declination or latitude in degrees */ { double x, y, x2, y2, x3, y3, r2; double xi, xir, eta, etar, raoff, ra, dec, ra0, dec0; double twopi = 6.28318530717959; double ctan, ccos; int ncoeff1 = wcs->ncoeff1; int ncoeff2 = wcs->ncoeff2; /* Ignore magnitude and color terms double mag = 0.0; double color = 0.0; */ /* Convert from pixels to millimeters */ x = xpix - wcs->crpix[0]; y = ypix - wcs->crpix[1]; x2 = x * x; y2 = y * y; x3 = x * x2; y3 = y * y2; r2 = x2 + y2; /* Compute xi,eta coordinates in degrees from x,y and plate model */ xi = wcs->x_coeff[ 0] + wcs->x_coeff[ 1]*x + wcs->x_coeff[ 2]*y + wcs->x_coeff[ 3]*x2 + wcs->x_coeff[ 4]*y2 + wcs->x_coeff[ 5]*x*y; if (ncoeff1 > 6) xi = xi + wcs->x_coeff[ 6]*x3 + wcs->x_coeff[ 7]*y3; if (ncoeff1 > 8) { xi = xi + wcs->x_coeff[ 8]*x2*y + wcs->x_coeff[ 9]*x*y2 + wcs->x_coeff[10]*(r2) + wcs->x_coeff[11]*x*r2 + wcs->x_coeff[12]*y*r2; } eta = wcs->y_coeff[ 0] + wcs->y_coeff[ 1]*x + wcs->y_coeff[ 2]*y + wcs->y_coeff[ 3]*x2 + wcs->y_coeff[ 4]*y2 + wcs->y_coeff[ 5]*x*y; if (ncoeff2 > 6) eta = eta + wcs->y_coeff[ 6]*x3 + wcs->y_coeff[ 7]*y3; if (ncoeff2 > 8) { eta = eta + wcs->y_coeff[ 8]*x2*y + wcs->y_coeff[ 9]*y2*x + wcs->y_coeff[10]*r2 + wcs->y_coeff[11]*x*r2 + wcs->y_coeff[12]*y*r2; } /* Convert to radians */ xir = degrad (xi); etar = degrad (eta); /* Convert to RA and Dec */ ra0 = degrad (wcs->crval[0]); dec0 = degrad (wcs->crval[1]); ctan = tan (dec0); ccos = cos (dec0); raoff = atan2 (xir / ccos, 1.0 - etar * ctan); ra = raoff + ra0; if (ra < 0.0) ra = ra + twopi; *xpos = raddeg (ra); dec = atan (cos (raoff) / ((1.0 - (etar * ctan)) / (etar + ctan))); *ypos = raddeg (dec); return 0; } int platepix (xpos, ypos, wcs, xpix, ypix) /* Routine to determine pixel coordinates for sky position */ /* returns 0 if successful otherwise 1 = angle too large for projection; */ /* based on amdinv() from getimage */ /* Input: */ double xpos; /* Right ascension or longitude in degrees */ double ypos; /* Declination or latitude in degrees */ struct WorldCoor *wcs; /* WCS parameter structure */ /* Output: */ double *xpix; /* x pixel number (RA or long without rotation) */ double *ypix; /* y pixel number (dec or lat without rotation) */ { double xi,eta,x,y,xy,x2,y2,x2y,y2x,x3,y3,r2,dx,dy; double tdec,ctan,ccos,traoff, craoff, etar, xir; double f,fx,fy,g,gx,gy; double ra0, dec0, ra, dec; double tolerance = 0.0000005; int max_iterations = 50; int i; int ncoeff1 = wcs->ncoeff1; int ncoeff2 = wcs->ncoeff2; /* Convert RA and Dec in radians to standard coordinates on a plate */ ra = degrad (xpos); dec = degrad (ypos); tdec = tan (dec); ra0 = degrad (wcs->crval[0]); dec0 = degrad (wcs->crval[1]); ctan = tan (dec0); ccos = cos (dec0); traoff = tan (ra - ra0); craoff = cos (ra - ra0); etar = (1.0 - ctan * craoff / tdec) / (ctan + (craoff / tdec)); xir = traoff * ccos * (1.0 - (etar * ctan)); xi = raddeg (xir); eta = raddeg (etar); /* Set initial value for x,y */ x = xi * wcs->dc[0] + eta * wcs->dc[1]; y = xi * wcs->dc[2] + eta * wcs->dc[3]; /* if (wcs->x_coeff[1] == 0.0) x = xi - wcs->x_coeff[0]; else x = (xi - wcs->x_coeff[0]) / wcs->x_coeff[1]; if (wcs->y_coeff[2] == 0.0) y = eta - wcs->y_coeff[0]; else y = (eta - wcs->y_coeff[0]) / wcs->y_coeff[2]; */ /* Iterate by Newton's method */ for (i = 0; i < max_iterations; i++) { /* X plate model */ xy = x * y; x2 = x * x; y2 = y * y; x3 = x2 * x; y3 = y2 * y; x2y = x2 * y; y2x = y2 * x; r2 = x2 + y2; f = wcs->x_coeff[0] + wcs->x_coeff[1]*x + wcs->x_coeff[2]*y + wcs->x_coeff[3]*x2 + wcs->x_coeff[4]*y2 + wcs->x_coeff[5]*xy; /* Derivative of X model wrt x */ fx = wcs->x_coeff[1] + wcs->x_coeff[3]*2.0*x + wcs->x_coeff[5]*y; /* Derivative of X model wrt y */ fy = wcs->x_coeff[2] + wcs->x_coeff[4]*2.0*y + wcs->x_coeff[5]*x; if (ncoeff1 > 6) { f = f + wcs->x_coeff[6]*x3 + wcs->x_coeff[7]*y3; fx = fx + wcs->x_coeff[6]*3.0*x2; fy = fy + wcs->x_coeff[7]*3.0*y2; } if (ncoeff1 > 8) { f = f + wcs->x_coeff[8]*x2y + wcs->x_coeff[9]*y2x + wcs->x_coeff[10]*r2 + wcs->x_coeff[11]*x*r2 + wcs->x_coeff[12]*y*r2; fx = fx + wcs->x_coeff[8]*2.0*xy + wcs->x_coeff[9]*y2 + wcs->x_coeff[10]*2.0*x + wcs->x_coeff[11]*(3.0*x2+y2) + wcs->x_coeff[12]*2.0*xy; fy = fy + wcs->x_coeff[8]*x2 + wcs->x_coeff[9]*2.0*xy + wcs->x_coeff[10]*2.0*y + wcs->x_coeff[11]*2.0*xy + wcs->x_coeff[12]*(3.0*y2+x2); } /* Y plate model */ g = wcs->y_coeff[0] + wcs->y_coeff[1]*x + wcs->y_coeff[2]*y + wcs->y_coeff[3]*x2 + wcs->y_coeff[4]*y2 + wcs->y_coeff[5]*xy; /* Derivative of Y model wrt x */ gx = wcs->y_coeff[1] + wcs->y_coeff[3]*2.0*x + wcs->y_coeff[5]*y; /* Derivative of Y model wrt y */ gy = wcs->y_coeff[2] + wcs->y_coeff[4]*2.0*y + wcs->y_coeff[5]*x; if (ncoeff2 > 6) { g = g + wcs->y_coeff[6]*x3 + wcs->y_coeff[7]*y3; gx = gx + wcs->y_coeff[6]*3.0*x2; gy = gy + wcs->y_coeff[7]*3.0*y2; } if (ncoeff2 > 8) { g = g + wcs->y_coeff[8]*x2y + wcs->y_coeff[9]*y2x + wcs->y_coeff[10]*r2 + wcs->y_coeff[11]*x*r2 + wcs->y_coeff[12]*y*r2; gx = gx + wcs->y_coeff[8]*2.0*xy + wcs->y_coeff[9]*y2 + wcs->y_coeff[10]*2.0*x + wcs->y_coeff[11]*(3.0*x2+y2) + wcs->y_coeff[12]*2.0*xy; gy = gy + wcs->y_coeff[8]*x2 + wcs->y_coeff[9]*2.0*xy + wcs->y_coeff[10]*2.0*y + wcs->y_coeff[11]*2.0*xy + wcs->y_coeff[12]*(3.0*y2+x2); } f = f - xi; g = g - eta; dx = ((-f * gy) + (g * fy)) / ((fx * gy) - (fy * gx)); dy = ((-g * fx) + (f * gx)) / ((fx * gy) - (fy * gx)); x = x + dx; y = y + dy; if ((fabs(dx) < tolerance) && (fabs(dy) < tolerance)) break; } /* Convert from plate pixels to image pixels */ *xpix = x + wcs->crpix[0]; *ypix = y + wcs->crpix[1]; /* If position is off of the image, return offscale code */ if (*xpix < 0.5 || *xpix > wcs->nxpix+0.5) return -1; if (*ypix < 0.5 || *ypix > wcs->nypix+0.5) return -1; return 0; } /* Set plate fit coefficients in structure from arguments */ int SetPlate (wcs, ncoeff1, ncoeff2, coeff) struct WorldCoor *wcs; /* World coordinate system structure */ int ncoeff1; /* Number of coefficients for x */ int ncoeff2; /* Number of coefficients for y */ double *coeff; /* Plate fit coefficients */ { int i; if (nowcs (wcs) || (ncoeff1 < 1 && ncoeff2 < 1)) return 1; wcs->ncoeff1 = ncoeff1; wcs->ncoeff2 = ncoeff2; wcs->prjcode = WCS_PLT; for (i = 0; i < 20; i++) { if (i < ncoeff1) wcs->x_coeff[i] = coeff[i]; else wcs->x_coeff[i] = 0.0; } for (i = 0; i < 20; i++) { if (i < ncoeff2) wcs->y_coeff[i] = coeff[ncoeff1+i]; else wcs->y_coeff[i] = 0.0; } return 0; } /* Return plate fit coefficients from structure in arguments */ int GetPlate (wcs, ncoeff1, ncoeff2, coeff) struct WorldCoor *wcs; /* World coordinate system structure */ int *ncoeff1; /* Number of coefficients for x */ int *ncoeff2; /* Number of coefficients for y) */ double *coeff; /* Plate fit coefficients */ { int i; if (nowcs (wcs)) return 1; *ncoeff1 = wcs->ncoeff1; *ncoeff2 = wcs->ncoeff2; for (i = 0; i < *ncoeff1; i++) coeff[i] = wcs->x_coeff[i]; for (i = 0; i < *ncoeff2; i++) coeff[*ncoeff1+i] = wcs->y_coeff[i]; return 0; } /* Set FITS header plate fit coefficients from structure */ void SetFITSPlate (header, wcs) char *header; /* Image FITS header */ struct WorldCoor *wcs; /* WCS structure */ { char keyword[16]; int i; for (i = 0; i < wcs->ncoeff1; i++) { sprintf (keyword,"CO1_%d",i+1); hputnr8 (header, keyword, -15, wcs->x_coeff[i]); } for (i = 0; i < wcs->ncoeff2; i++) { sprintf (keyword,"CO2_%d",i+1); hputnr8 (header, keyword, -15, wcs->y_coeff[i]); } return; } /* Mar 27 1998 New subroutines for direct image pixel <-> sky polynomials * Apr 10 1998 Make terms identical for both x and y polynomials * Apr 10 1998 Allow different numbers of coefficients for x and y * Apr 16 1998 Drom NCOEFF header parameter * Apr 28 1998 Change projection flags to WCS_* * Sep 10 1998 Check for xc1 and yc2 divide by zero after Allen Harris, SAO * * Oct 21 1999 Drop unused variables after lint * * Feb 29 2000 Use inverse CD matrix to get initial X,Y in platepix() * as suggested by Paolo Montegriffo from Bologna Ast. Obs. */