JSOC_Documentation: proj/cgem/prep/apps/img2helioVector.c Source File

00001 #include <math.h>
00002 
00003 int img2helioVector (double bxImg, double byImg, double bzImg, double *bxHelio, 
00004                      double *byHelio, double *bzHelio, double lon, double lat,
00005                      double lonc, double latc, double pAng) {
00006 /*
00007 *     perform tramsformation of a vector from image location (lon, lat) to
00008 *     heliographic center. The formula is from Hagyard (1987), and further
00009 *     developed by Gary & Hagyard (1990).
00010 *
00011 * Arguments:
00012 *
00013 *    bxImg, byImg, bzImg: three components of vector magnetic field on image
00014 *                         coordinates.
00015 *    lon, lat:            heliographic coordinates of the location where the vector field
00016 *                         measured. They are in radians.
00017 *    lonc, latc:          heliographic coordinates of the image disk center. They are in
00018 *                         radians.
00019 *    pAng:                position angle of the heliographic north pole, measured eastward
00020 *                         from the north. It's in radians.   
00021 */
00022 
00023     static double raddeg = M_PI / 180.;
00024     double a11, a12, a13, a21, a22, a23, a31, a32, a33;
00025 
00026     a11 = -sin(latc) * sin(pAng) * sin(lon - lonc) + cos(pAng) * cos(lon - lonc);
00027     a12 =  sin(latc) * cos(pAng) * sin(lon - lonc) + sin(pAng) * cos(lon - lonc);
00028     a13 = -cos(latc) * sin(lon - lonc);
00029     a21 = -sin(lat) * (sin(latc) * sin(pAng) * cos(lon - lonc) + cos(pAng) * sin(lon - lonc)) 
00030           - cos(lat) * cos(latc) * sin(pAng);
00031     a22 =  sin(lat) * (sin(latc) * cos(pAng) * cos(lon - lonc) - sin(pAng) * sin(lon - lonc))
00032           + cos(lat) * cos(latc) * cos(pAng);
00033     a23 = -cos(latc) * sin(lat) * cos(lon - lonc) + sin(latc) * cos(lat);
00034     a31 =  cos(lat) * (sin(latc) * sin(pAng) * cos(lon - lonc) + cos(pAng) * sin(lon - lonc))
00035           - sin(lat) * cos(latc) * sin(pAng);
00036     a32 = -cos(lat) * (sin(latc) * cos(pAng) * cos(lon - lonc) - sin(pAng) * sin(lon - lonc))
00037           + sin(lat) * cos(latc) * cos(pAng);
00038     a33 =  cos(lat) * cos(latc) * cos(lon - lonc) + sin(lat) * sin(latc);
00039 
00040     *bxHelio = a11 * bxImg + a12 * byImg + a13 * bzImg;
00041     *byHelio = a21 * bxImg + a22 * byImg + a23 * bzImg;
00042     *bzHelio = a31 * bxImg + a32 * byImg + a33 * bzImg;
00043 
00044 return 0;
00045 }