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/*** File saoimage/wcslib/dsspos.c
*** October 21, 1999
*** By Doug Mink, dmink@cfa.harvard.edu
*** Harvard-Smithsonian Center for Astrophysics
* Module: dsspos.c (Plate solution WCS conversion)
* Purpose: Compute WCS from Digital Sky Survey plate fit
* Subroutine: dsspos() converts from pixel location to RA,Dec
* Subroutine: dsspix() 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 <math.h>
#include <string.h>
#include <stdio.h>
#include "vimoswcs.h"
int
dsspos (xpix, ypix, vimoswcs, 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 *vimoswcs; /* WCS parameter structure */
/* Output: */
double *xpos; /* Right ascension or longitude in degrees */
double *ypos; /* Declination or latitude in degrees */
{
double x, y, xmm, ymm, xmm2, ymm2, xmm3, ymm3, x2y2;
double xi, xir, eta, etar, raoff, ra, dec;
double cond2r = 1.745329252e-2;
double cons2r = 206264.8062470964;
double twopi = 6.28318530717959;
double ctan, ccos;
/* Ignore magnitude and color terms
double mag = 0.0;
double color = 0.0; */
/* Convert from image pixels to plate pixels */
x = xpix + vimoswcs->x_pixel_offset - 1.0 + 0.5;
y = ypix + vimoswcs->y_pixel_offset - 1.0 + 0.5;
/* Convert from pixels to millimeters */
xmm = (vimoswcs->ppo_coeff[2] - x * vimoswcs->x_pixel_size) / 1000.0;
ymm = (y * vimoswcs->y_pixel_size - vimoswcs->ppo_coeff[5]) / 1000.0;
xmm2 = xmm * xmm;
ymm2 = ymm * ymm;
xmm3 = xmm * xmm2;
ymm3 = ymm * ymm2;
x2y2 = xmm2 + ymm2;
/* Compute coordinates from x,y and plate model */
xi = vimoswcs->x_coeff[ 0]*xmm + vimoswcs->x_coeff[ 1]*ymm +
vimoswcs->x_coeff[ 2] + vimoswcs->x_coeff[ 3]*xmm2 +
vimoswcs->x_coeff[ 4]*xmm*ymm + vimoswcs->x_coeff[ 5]*ymm2 +
vimoswcs->x_coeff[ 6]*(x2y2) + vimoswcs->x_coeff[ 7]*xmm3 +
vimoswcs->x_coeff[ 8]*xmm2*ymm + vimoswcs->x_coeff[ 9]*xmm*ymm2 +
vimoswcs->x_coeff[10]*ymm3 + vimoswcs->x_coeff[11]*xmm*(x2y2) +
vimoswcs->x_coeff[12]*xmm*x2y2*x2y2;
/* Ignore magnitude and color terms
+ vimoswcs->x_coeff[13]*mag + vimoswcs->x_coeff[14]*mag*mag +
vimoswcs->x_coeff[15]*mag*mag*mag + vimoswcs->x_coeff[16]*mag*xmm +
vimoswcs->x_coeff[17]*mag*x2y2 + vimoswcs->x_coeff[18]*mag*xmm*x2y2 +
vimoswcs->x_coeff[19]*color; */
eta = vimoswcs->y_coeff[ 0]*ymm + vimoswcs->y_coeff[ 1]*xmm +
vimoswcs->y_coeff[ 2] + vimoswcs->y_coeff[ 3]*ymm2 +
vimoswcs->y_coeff[ 4]*xmm*ymm + vimoswcs->y_coeff[ 5]*xmm2 +
vimoswcs->y_coeff[ 6]*(x2y2) + vimoswcs->y_coeff[ 7]*ymm3 +
vimoswcs->y_coeff[ 8]*ymm2*xmm + vimoswcs->y_coeff[ 9]*ymm*xmm2 +
vimoswcs->y_coeff[10]*xmm3 + vimoswcs->y_coeff[11]*ymm*(x2y2) +
vimoswcs->y_coeff[12]*ymm*x2y2*x2y2;
/* Ignore magnitude and color terms
+ vimoswcs->y_coeff[13]*mag + vimoswcs->y_coeff[14]*mag*mag +
vimoswcs->y_coeff[15]*mag*mag*mag + vimoswcs->y_coeff[16]*mag*ymm +
vimoswcs->y_coeff[17]*mag*x2y2) + vimoswcs->y_coeff[18]*mag*ymm*x2y2 +
vimoswcs->y_coeff[19]*color; */
/* Convert to radians */
xir = xi / cons2r;
etar = eta / cons2r;
/* Convert to RA and Dec */
ctan = tan (vimoswcs->plate_dec);
ccos = cos (vimoswcs->plate_dec);
raoff = atan2 (xir / ccos, 1.0 - etar * ctan);
ra = raoff + vimoswcs->plate_ra;
if (ra < 0.0) ra = ra + twopi;
*xpos = ra / cond2r;
dec = atan (cos (raoff) * ((etar + ctan) / (1.0 - (etar * ctan))));
*ypos = dec / cond2r;
return 0;
}
int
dsspix (xpos, ypos, vimoswcs, 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 *vimoswcs; /* 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 div,xi,eta,x,y,xy,x2,y2,x2y,y2x,x3,y3,x4,y4,x2y2,cjunk,dx,dy;
double sypos,cypos,syplate,cyplate,sxdiff,cxdiff;
double f,fx,fy,g,gx,gy, xmm, ymm;
double conr2s = 206264.8062470964;
double tolerance = 0.0000005;
int max_iterations = 50;
int i;
double xr, yr; /* position in radians */
*xpix = 0.0;
*ypix = 0.0;
/* Convert RA and Dec in radians to standard coordinates on a plate */
xr = degrad (xpos);
yr = degrad (ypos);
sypos = sin (yr);
cypos = cos (yr);
if (vimoswcs->plate_dec == 0.0)
vimoswcs->plate_dec = degrad (vimoswcs->yref);
syplate = sin (vimoswcs->plate_dec);
cyplate = cos (vimoswcs->plate_dec);
if (vimoswcs->plate_ra == 0.0)
vimoswcs->plate_ra = degrad (vimoswcs->yref);
sxdiff = sin (xr - vimoswcs->plate_ra);
cxdiff = cos (xr - vimoswcs->plate_ra);
div = (sypos * syplate) + (cypos * cyplate * cxdiff);
if (div == 0.0)
return (1);
xi = cypos * sxdiff * conr2s / div;
eta = ((sypos * cyplate) - (cypos * syplate * cxdiff)) * conr2s / div;
/* Set initial value for x,y */
if (vimoswcs->plate_scale == 0.0)
return (1);
xmm = xi / vimoswcs->plate_scale;
ymm = eta / vimoswcs->plate_scale;
/* Iterate by Newton's method */
for (i = 0; i < max_iterations; i++) {
/* X plate model */
xy = xmm * ymm;
x2 = xmm * xmm;
y2 = ymm * ymm;
x2y = x2 * ymm;
y2x = y2 * xmm;
x2y2 = x2 + y2;
cjunk = x2y2 * x2y2;
x3 = x2 * xmm;
y3 = y2 * ymm;
x4 = x2 * x2;
y4 = y2 * y2;
f = vimoswcs->x_coeff[0]*xmm + vimoswcs->x_coeff[1]*ymm +
vimoswcs->x_coeff[2] + vimoswcs->x_coeff[3]*x2 +
vimoswcs->x_coeff[4]*xy + vimoswcs->x_coeff[5]*y2 +
vimoswcs->x_coeff[6]*x2y2 + vimoswcs->x_coeff[7]*x3 +
vimoswcs->x_coeff[8]*x2y + vimoswcs->x_coeff[9]*y2x +
vimoswcs->x_coeff[10]*y3 + vimoswcs->x_coeff[11]*xmm*x2y2 +
vimoswcs->x_coeff[12]*xmm*cjunk;
/* magnitude and color terms ignored
+ vimoswcs->x_coeff[13]*mag +
vimoswcs->x_coeff[14]*mag*mag + vimoswcs->x_coeff[15]*mag*mag*mag +
vimoswcs->x_coeff[16]*mag*xmm + vimoswcs->x_coeff[17]*mag*(x2+y2) +
vimoswcs->x_coeff[18]*mag*xmm*(x2+y2) + vimoswcs->x_coeff[19]*color;
*/
/* Derivative of X model wrt x */
fx = vimoswcs->x_coeff[0] + vimoswcs->x_coeff[3]*2.0*xmm +
vimoswcs->x_coeff[4]*ymm + vimoswcs->x_coeff[6]*2.0*xmm +
vimoswcs->x_coeff[7]*3.0*x2 + vimoswcs->x_coeff[8]*2.0*xy +
vimoswcs->x_coeff[9]*y2 + vimoswcs->x_coeff[11]*(3.0*x2+y2) +
vimoswcs->x_coeff[12]*(5.0*x4 +6.0*x2*y2+y4);
/* magnitude and color terms ignored
vimoswcs->x_coeff[16]*mag + vimoswcs->x_coeff[17]*mag*2.0*xmm +
vimoswcs->x_coeff[18]*mag*(3.0*x2+y2);
*/
/* Derivative of X model wrt y */
fy = vimoswcs->x_coeff[1] + vimoswcs->x_coeff[4]*xmm +
vimoswcs->x_coeff[5]*2.0*ymm + vimoswcs->x_coeff[6]*2.0*ymm +
vimoswcs->x_coeff[8]*x2 + vimoswcs->x_coeff[9]*2.0*xy +
vimoswcs->x_coeff[10]*3.0*y2 + vimoswcs->x_coeff[11]*2.0*xy +
vimoswcs->x_coeff[12]*4.0*xy*x2y2;
/* magnitude and color terms ignored
vimoswcs->x_coeff[17]*mag*2.0*ymm +
vimoswcs->x_coeff[18]*mag*2.0*xy;
*/
/* Y plate model */
g = vimoswcs->y_coeff[0]*ymm + vimoswcs->y_coeff[1]*xmm +
vimoswcs->y_coeff[2] + vimoswcs->y_coeff[3]*y2 +
vimoswcs->y_coeff[4]*xy + vimoswcs->y_coeff[5]*x2 +
vimoswcs->y_coeff[6]*x2y2 + vimoswcs->y_coeff[7]*y3 +
vimoswcs->y_coeff[8]*y2x + vimoswcs->y_coeff[9]*x2y +
vimoswcs->y_coeff[10]*x3 + vimoswcs->y_coeff[11]*ymm*x2y2 +
vimoswcs->y_coeff[12]*ymm*cjunk;
/* magnitude and color terms ignored
vimoswcs->y_coeff[13]*mag + vimoswcs->y_coeff[14]*mag*mag +
vimoswcs->y_coeff[15]*mag*mag*mag + vimoswcs->y_coeff[16]*mag*ymm +
vimoswcs->y_coeff[17]*mag*x2y2 +
vimoswcs->y_coeff[18]*mag*ymm*x2y2 + vimoswcs->y_coeff[19]*color;
*/
/* Derivative of Y model wrt x */
gx = vimoswcs->y_coeff[1] + vimoswcs->y_coeff[4]*ymm +
vimoswcs->y_coeff[5]*2.0*xmm + vimoswcs->y_coeff[6]*2.0*xmm +
vimoswcs->y_coeff[8]*y2 + vimoswcs->y_coeff[9]*2.0*xy +
vimoswcs->y_coeff[10]*3.0*x2 + vimoswcs->y_coeff[11]*2.0*xy +
vimoswcs->y_coeff[12]*4.0*xy*x2y2;
/* magnitude and color terms ignored
vimoswcs->y_coeff[17]*mag*2.0*xmm +
vimoswcs->y_coeff[18]*mag*ymm*2.0*xmm;
*/
/* Derivative of Y model wrt y */
gy = vimoswcs->y_coeff[0] + vimoswcs->y_coeff[3]*2.0*ymm +
vimoswcs->y_coeff[4]*xmm + vimoswcs->y_coeff[6]*2.0*ymm +
vimoswcs->y_coeff[7]*3.0*y2 + vimoswcs->y_coeff[8]*2.0*xy +
vimoswcs->y_coeff[9]*x2 + vimoswcs->y_coeff[11]*(x2+3.0*y2) +
vimoswcs->y_coeff[12]*(5.0*y4 + 6.0*x2*y2 + x4);
/* magnitude and color terms ignored
vimoswcs->y_coeff[16]*mag + vimoswcs->y_coeff[17]*mag*2.0*ymm +
vimoswcs->y_coeff[18]*mag*(x2+3.0*y2);
*/
f = f - xi;
g = g - eta;
dx = ((-f * gy) + (g * fy)) / ((fx * gy) - (fy * gx));
dy = ((-g * fx) + (f * gx)) / ((fx * gy) - (fy * gx));
xmm = xmm + dx;
ymm = ymm + dy;
if ((fabs(dx) < tolerance) && (fabs(dy) < tolerance)) break;
}
/* Convert mm from plate center to plate pixels */
if (vimoswcs->x_pixel_size == 0.0 || vimoswcs->y_pixel_size == 0.0)
return (1);
x = (vimoswcs->ppo_coeff[2] - xmm*1000.0) / vimoswcs->x_pixel_size;
y = (vimoswcs->ppo_coeff[5] + ymm*1000.0) / vimoswcs->y_pixel_size;
/* Convert from plate pixels to image pixels */
*xpix = x - vimoswcs->x_pixel_offset + 1.0 - 0.5;
*ypix = y - vimoswcs->y_pixel_offset + 1.0 - 0.5;
/* If position is off of the image, return offscale code */
if (*xpix < 0.5 || *xpix > vimoswcs->nxpix+0.5)
return -1;
if (*ypix < 0.5 || *ypix > vimoswcs->nypix+0.5)
return -1;
return 0;
}
/* Mar 6 1995 Original version of this code
* May 4 1995 Fix eta cross terms which were all in y
* Jun 21 1995 Add inverse routine
* Oct 17 1995 Fix inverse routine (degrees -> radians)
* Nov 7 1995 Add half pixel to image coordinates to get astrometric
* plate coordinates
* Feb 26 1996 Fix plate to image pixel conversion error
*
* Mar 23 1998 Change names from plate*() to dss*()
* Apr 7 1998 Change amd_i_coeff to i_coeff
* Sep 4 1998 Fix possible divide by zero in dsspos() from Allen Harris, SAO
* Sep 10 1998 Fix possible divide by zero in dsspix() from Allen Harris, SAO
*
* Oct 21 1999 Drop declaration of cond2r in dsspix()
*/
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