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/**
* @file
*
* @date Created on Jan 9, 2025
* @author Attila Kovacs
*
* Example file for using the SuperNOVAS C/C++ library for determining positions for
* Solary-system sources, with the CALCEPH C library providing access to ephemeris
* files.
*
* You will need access to the CALCEPH library (unversioned `libcalceph.so` or else
* `libcalceph.a`) and C headers (`calceph.h`), and the SuperNOVAS
* `libsolsys-calceph.so` (or `libsolsys-calceph.a`) module.
*
* Link with:
*
* ```
* -lsupernovas -lsolsys-calceph -lcalceph
* ```
*/
#define _POSIX_C_SOURCE 199309L ///< for clock_gettime()
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <novas.h> ///< SuperNOVAS functions and definitions
#include <novas-calceph.h> ///< CALCEPH adapter functions to SuperNOVAS
// Below are some Earth orientation values. Here we define them as constants, but they may
// of course be variables. They should be set to the appropriate values for the time
// of observation based on the IERS Bulletins...
#define LEAP_SECONDS 37 ///< [s] current leap seconds from IERS Bulletin C
#define DUT1 0.114 ///< [s] current UT1 - UTC time difference from IERS Bulletin A
#define POLAR_DX 230.0 ///< [mas] Earth polar offset x, e.g. from IERS Bulletin A.
#define POLAR_DY -62.0 ///< [mas] Earth polar offset y, e.g. from IERS Bulletin A.
int main(int argc, char *argv[]) {
// Program Options -------------------------------------------------------->
char *datafile = "/path/to/de440s.bsp"; // Ephemeris file to use
// SuperNOVAS variables used for the calculations ------------------------->
object source; // observed source
observer obs; // observer location
novas_timespec obs_time; // astrometric time of observation
novas_frame obs_frame; // observing frame defined for observing time and location
enum novas_accuracy accuracy; // NOVAS_FULL_ACCURACY or NOVAS_REDUCED_ACCURACY
sky_pos apparent; // calculated precise observed (apparent) position of source
// Calculated quantities ------------------------------------------------->
double az, el; // calculated azimuth and elevation at observing site
// Intermediate variables we'll use -------------------------------------->
t_calcephbin *de440; // CALCEPH ephemeris binary
// Command line argument can define the ephemeris data to use.
if(argc > 1)
datafile = argv[1];
// We'll print debugging messages and error traces...
novas_debug(NOVAS_DEBUG_ON);
// -------------------------------------------------------------------------
// We'll use the CALCEPH library to provide ephemeris data
// First open one or more ephemeris files with CALCEPH to use
// E.g. the DE440 (short-term) ephemeris data from JPL.
de440 = calceph_open(datafile);
if(!de440) {
fprintf(stderr, "ERROR! could not open ephemeris data\n");
return 1;
}
// Make de440 provide ephemeris data for the major planets.
novas_use_calceph_planets(de440);
// We could specify to use a calceph ephemeris binary for generic
// Solar-systems sources also (including planets too if
// novas_use_calceph_planets() is not called separately
//
// E.g. Jovian satellites:
// t_calcephbin jovian = calceph_open("/path/to/jup365.bsp");
// novas_use_calceph(jovian);
// Since we have an ephemeris provider for major planets, we can unlock the
// ultimate accuracy of SuperNOVAS.
accuracy = NOVAS_FULL_ACCURACY; // sub-uas precision
// -------------------------------------------------------------------------
// Define a Solar-system source
// To define a major planet (or Sun, Moon, SSB, or EMB):
if(make_planet(NOVAS_MARS, &source) != 0) {
fprintf(stderr, "ERROR! defining planet.\n");
return 1;
}
// ... Or, to define a minor body, such as an asteroid or satellite
// with a name and ID number.
/*
if(make_ephem_object("Io", 501, &source) != 0) {
fprintf(stderr, "ERROR! defining ephemeris body.\n");
return 1;
}
*/
/*
// If the object uses CALCEPH IDs instead of NAIF, then
novas_calceph_use_ids(NOVAS_ID_CALCEPH);
*/
// -------------------------------------------------------------------------
// Define observer somewhere on Earth (we can also define observers in Earth
// or Sun orbit, at the geocenter or at the Solary-system barycenter...)
// Specify the location we are observing from
// 50.7374 deg N, 7.0982 deg E, 60m elevation (GPS / WGS84)
// (You can set local weather parameters after...)
if(make_gps_observer(50.7374, 7.0982, 60.0, &obs) != 0) {
fprintf(stderr, "ERROR! defining Earth-based observer location.\n");
return 1;
}
// -------------------------------------------------------------------------
// Set the astrometric time of observation...
// Set the time of observation to the current UTC-based UNIX time
if(novas_set_current_time(LEAP_SECONDS, DUT1, &obs_time) != 0) {
fprintf(stderr, "ERROR! failed to set time of observation.\n");
return 1;
}
// ... Or you could set a time explicily in any known timescale.
/*
// Let's set a TDB-based time for the start of the J2000 epoch exactly...
if(novas_set_time(NOVAS_TDB, NOVAS_JD_J2000, 32, 0.0, &obs_time) != 0) {
fprintf(stderr, "ERROR! failed to set time of observation.\n");
return 1;
}
*/
// -------------------------------------------------------------------------
// Initialize the observing frame with the given observing and Earth
// orientation patameters.
//
if(novas_make_frame(accuracy, &obs, &obs_time, POLAR_DX, POLAR_DY, &obs_frame) != 0) {
fprintf(stderr, "ERROR! failed to define observing frame.\n");
return 1;
}
// -------------------------------------------------------------------------
// Calculate the precise apparent position (e.g. in CIRS).
if(novas_sky_pos(&source, &obs_frame, NOVAS_CIRS, &apparent) != 0) {
fprintf(stderr, "ERROR! failed to calculate apparent position.\n");
return 1;
}
// Let's print the apparent position in CIRS
// (Note, CIRS R.A. is relative to CIO, not the true equinox of date.)
printf(" RA = %.9f h, Dec = %.9f deg, rad_vel = %.6f km/s\n", apparent.ra, apparent.dec, apparent.rv);
// -------------------------------------------------------------------------
// Convert the apparent position in CIRS on sky to horizontal coordinates
// We'll use a standard (fixed) atmospheric model to estimate an optical refraction
// (You might use other refraction models, or NULL to ignore refraction corrections)
if(novas_app_to_hor(&obs_frame, NOVAS_CIRS, apparent.ra, apparent.dec, novas_standard_refraction, &az, &el) != 0) {
fprintf(stderr, "ERROR! failed to calculate azimuth / elevation.\n");
return 1;
}
// Let's print the calculated azimuth and elevation
printf(" Az = %.6f deg, El = %.6f deg\n", az, el);
return 0;
}
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