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alt_az.cpp
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/
alt_az.cpp
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/* alt_az.cpp: functions for coordinate conversions
Copyright (C) 2010, Project Pluto
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA. */
#include <math.h>
#include <stdio.h>
#include "watdefs.h"
#include "afuncs.h"
#include "lunar.h"
#define PI 3.1415926535897932384626433832795028841971693993751058209749445923
#define CONVERT (1000000. * 180. / PI)
#define TWO_PI (2. * PI)
#define J2000 2451545.0
static void ra_dec_to_alt_az( const double hr_ang, const double dec,
double DLLPTR *alt, double DLLPTR *az, const double lat)
{
double temp, cos_lat = cos( lat);
*alt = asine( sin( lat) * sin( dec) + cos_lat * cos( dec) * cos( hr_ang));
if( cos_lat < .00001) /* polar case */
*az = hr_ang;
else
{
temp = (sin( dec) - sin( *alt) * sin( lat)) / (cos( *alt) * cos_lat);
temp = PI - acose( temp);
*az = ((sin( hr_ang) < 0.) ? temp : -temp);
}
}
/* Normally, the following will take the J2000 RA/dec and compute
the mean location at the epoch given by 'jd_utc'. The result is
then stored in *loc_epoch. However, one can pass a NULL RA/dec;
in that case, it's assumed that the location at epoch is already
stored in *loc_epoch. The hour angle and nutation are then computed,
and the alt/azimuth. You can optionally pass in NULLs for 'hr_ang'
and 'loc_epoch' in the (rather common) situations where you're
really just interested in the alt/az. */
void DLL_FUNC full_ra_dec_to_alt_az( const DPT DLLPTR *ra_dec,
DPT DLLPTR *alt_az,
DPT DLLPTR *loc_epoch, const DPT DLLPTR *latlon,
const double jd_utc, double DLLPTR *hr_ang)
{
double ha, nutation_lon;
const double t_centuries = (jd_utc - J2000) / 36525.;
const double cos_obliq_2000 = 0.917482062069181825744000384639406458043;
DPT loc_at_epoch;
if( ra_dec)
precess_pt( &loc_at_epoch, ra_dec, 2000., 2000. + t_centuries * 100.);
else /* no RA/dec at J2000 supplied */
loc_at_epoch = *loc_epoch;
ha = -loc_at_epoch.x - (green_sidereal_time( jd_utc) + latlon->x);
nutation( t_centuries, &nutation_lon, NULL);
ha -= cos_obliq_2000 * nutation_lon * (PI / 180.) / 3600.;
ha = fmod( ha, TWO_PI);
if( ha > PI) ha -= TWO_PI;
if( ha <-PI) ha += TWO_PI;
ra_dec_to_alt_az( ha, loc_at_epoch.y, &alt_az->y, &alt_az->x, latlon->y);
if( hr_ang)
*hr_ang = ha;
if( loc_epoch)
*loc_epoch = loc_at_epoch;
}
static void alt_az_to_ra_dec( double alt, double az,
double DLLPTR *hr_ang,
double DLLPTR *dec, const double lat)
{
double temp, sin_dec, cos_lat = cos( lat);
if( alt > PI / 2.)
{
alt = PI - alt;
az += PI;
}
if( alt < -PI / 2.)
{
alt = -PI - alt;
az -= PI;
}
sin_dec = sin( lat) * sin( alt) + cos_lat * cos( alt) * cos( az);
*dec = asine( sin_dec);
if( cos_lat < .00001) /* polar case */
*hr_ang = az + PI;
else
{
temp = cos_lat * cos( *dec);
temp = (sin( alt) - sin( lat) * sin_dec) / temp;
temp = acose( -temp);
if( sin( az) > 0.)
*hr_ang = PI - temp;
else
*hr_ang = PI + temp;
}
}
void DLL_FUNC full_alt_az_to_ra_dec( DPT DLLPTR *ra_dec,
const DPT DLLPTR *alt_az,
const double jd_utc, const DPT DLLPTR *latlon)
{
double hr_ang, ra;
DPT tmp;
alt_az_to_ra_dec( alt_az->y, alt_az->x, &hr_ang,
&tmp.y, latlon->y);
ra = hr_ang + green_sidereal_time( jd_utc) + latlon->x;
tmp.x = fmod( -ra, TWO_PI);
precess_pt( ra_dec, &tmp, 2000. + (jd_utc - J2000) / 365.25, 2000.);
}
/* The following matrix was derived from the code in 'superga2.cpp'. */
const double * DLL_FUNC j2000_to_supergalactic_matrix( void)
{
static const double rval[9] = {
0.37501548, 0.34135896, 0.86188018,
-0.89832046, -0.09572714, 0.42878511,
0.22887497, -0.93504565, 0.27075058 };
return( rval);
}
void DLL_FUNC ra_dec_to_supergalactic( const double ra, const double dec,
double DLLPTR *glat, double DLLPTR *glon)
{
double ipt[2], opt[2];
ipt[0] = ra;
ipt[1] = dec;
precess_ra_dec( j2000_to_supergalactic_matrix( ), opt, ipt, 0);
*glon = opt[0];
*glat = opt[1];
}
void DLL_FUNC supergalactic_to_ra_dec( const double glat, double glon,
double DLLPTR *ra, double DLLPTR *dec)
{
double ipt[2], opt[2];
ipt[0] = glon;
ipt[1] = glat;
precess_ra_dec( j2000_to_supergalactic_matrix( ), opt, ipt, 1);
*ra = opt[0];
*dec = opt[1];
}
const double * DLL_FUNC j2000_to_galactic_matrix( void)
{
/* The following matrix comes from _The Hipparcos & Tycho */
/* Catalogues: Introduction & Guide to the Data_, p 92: */
static const double rval[9] = {
-.0548755604, -.8734370902, -.4838350155,
.4941094279, -.4448296300, .7469822445,
-.8676661490, -.1980763734, .4559837762 };
return( rval);
}
void DLL_FUNC ra_dec_to_galactic( const double ra, const double dec,
double DLLPTR *glat, double DLLPTR *glon)
{
double ipt[2], opt[2];
ipt[0] = ra;
ipt[1] = dec;
precess_ra_dec( j2000_to_galactic_matrix( ), opt, ipt, 0);
*glon = opt[0];
*glat = opt[1];
}
void DLL_FUNC galactic_to_ra_dec( const double glat, double glon,
double DLLPTR *ra, double DLLPTR *dec)
{
double ipt[2], opt[2];
ipt[0] = glon;
ipt[1] = glat;
precess_ra_dec( j2000_to_galactic_matrix( ), opt, ipt, 1);
*ra = opt[0];
*dec = opt[1];
}
void DLL_FUNC precess_pt( DPT DLLPTR *opt, const DPT DLLPTR *ipt,
double from_time, double to_time)
{
double precess[9];
double temp_opt[2], temp_ipt[2];
int dir = 0;
if( from_time == to_time)
{
*opt = *ipt;
return;
}
if( from_time == 2000.)
{
from_time = to_time;
to_time = 2000.;
dir = 1;
}
setup_precession( precess, from_time, to_time);
temp_ipt[0] = -ipt->x;
temp_ipt[1] = ipt->y;
precess_ra_dec( precess, temp_opt, temp_ipt, dir);
opt->x = -temp_opt[0];
opt->y = temp_opt[1];
}