Subversion Repositories planix.SVN

#include "astro.h"

void
geo(void)
{

/*
 *      uses alpha, delta, rp
 */

/*
 *      sets ra, decl, lha, decl2, az, el
 */

/*
 *      geo converts geocentric equatorial coordinates
 *      to topocentric equatorial and topocentric horizon
 *      coordinates.
 *      All are (usually) referred to the true equator.
 */

        double sel, saz, caz;
        double f;
        double sa, ca, sd;

/*
 *      convert to local hour angle and declination
 */

        lha = gst - alpha - wlong;
        decl = delta;

/*
 *      compute diurnal parallax (requires geocentric latitude)
 */

        sa = cos(decl)*sin(lha);
        ca = cos(decl)*cos(lha) - erad*cos(glat)*sin(hp);
        sd = sin(decl)           - erad*sin(glat)*sin(hp);

        lha = atan2(sa, ca);
        decl2 = atan2(sd, sqrt(sa*sa+ca*ca));
        f = sqrt(sa*sa+ca*ca+sd*sd);
        semi2 = semi/f;
        ra = gst - lha - wlong;
        ra = pinorm(ra);

/*
 *      convert to horizon coordinates
 */

        sel = sin(nlat)*sin(decl2) + cos(nlat)*cos(decl2)*cos(lha);
        el = atan2(sel, pyth(sel));
        saz = sin(lha)*cos(decl2);
        caz = cos(nlat)*sin(decl2) - sin(nlat)*cos(decl2)*cos(lha);
        az = pi + atan2(saz, -caz);

        az /= radian;
        el /= radian;
}