/* Diurnal parallax, AA page D3 */#include "kep.h"/* Earth radii per au. */static double DISFAC;extern double aearth, au;/* distance to center of Earth, in Earth radii */extern double trho;/* observer's geocentric latitude, degrees */extern double tlat;int diurpx( last, ra, dec, dist )double last;  /* local apparent sidereal time, radians */double *ra;  /* right ascension, radians */double *dec; /* declination, radians */double dist; /* Earth - object distance, au */{double cosdec, sindec, coslat, sinlat;double p[3], dp[3], x, y, z, D;/* Don't bother with this unless the equatorial horizontal parallax * is at least 0.005" */if( dist > 1758.8 )	return(-1);DISFAC = au / (0.001 * aearth);cosdec = cos(*dec);sindec = sin(*dec);/* Observer's astronomical latitude */x = tlat * DTR;coslat = cos(x);sinlat = sin(x);/* Convert to equatorial rectangular coordinates * in which unit distance = earth radius */D = dist * DISFAC;p[0] = D*cosdec*cos(*ra);p[1] = D*cosdec*sin(*ra);p[2] = D*sindec;dp[0] = -trho*coslat*cos(last);dp[1] = -trho*coslat*sin(last);dp[2] = -trho*sinlat;x = p[0] + dp[0];y = p[1] + dp[1];z = p[2] + dp[2];D = x*x + y*y + z*z;D = sqrt(D);	/* topocentric distance *//* recompute ra and dec */*ra = zatan2(x,y);*dec = asin(z/D);showcor( "diurnal parallax", p, dp );return(0);}