demo2_sun_tracking.c

Repeated calculation (tracking) of the Sun using interpolation

void demo2(void)
/*! Sample code using the greatly simplified calculation of the position
 *  of the Sun using interpolated coordinates.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
{
    Sky_DeltaTs     deltaTs;        /* Differences between timescales */
    Sky_SiteProp    site;           /* Properties of the site */
    Sky_SiteHorizon topo;           /* Sun position, as seen from the site */
    double          j2kUtc_d;       /* Time, expressed as a count of days */
    char            azStr[24], elStr[24];
    int             i;
 
    /* Set up the various delta T values. Values are taken from Bulletin A of
     * 16-Jul-2020, using the approximate "DUT1" value for deltaUT_s */
    sky_initTime(37, -0.2, &deltaTs);
 
    /* Set up the fixed site data */
    sky_setSiteLocation(SITE_LATITUDE_deg,
                        SITE_LONGITUDE_deg,
                        SITE_HEIGHT_m,
                        &site);
    sky_setSiteTempPress(SITE_TEMPERATURE_degC,
                         SITE_PRESSURE_hPa,
                         &site);
    sky_setSiteTimeZone(SITE_TIMEZONE_h, &site);
 
    /* Get the current time in days since 2000-01-01 Greenwich noon */
    j2kUtc_d = sky_unixTimeToJ2kd(time(NULL));
 
    /* Set up the interpolation algorithm to calculate Sun positions  */
    skyfast_init(j2kUtc_d, 720, &deltaTs, &sun_nrelApparent);
 
    printf("Fast sun calculation\n");
    for (i = 0; i < 100; i++) {
        /* Get sun position using interpolation */
        j2kUtc_d = sky_unixTimeToJ2kd(time(NULL));
        sunTopocentricFast(j2kUtc_d, &deltaTs, &site, &topo);
 
        skyio_printJ2kd(j2kUtc_d + site.timeZone_d);
        skyio_radToDmsStr(azStr, sizeof(azStr), topo.azimuth_rad, 2);
        skyio_radToDmsStr(elStr, sizeof(elStr), topo.elevation_rad, 2);
        printf(" Sun Azimuth: %s, Elevation: %s\n", azStr, elStr);
 
        sleep(1);       /* Just use a simple delay for this demo. */
    }
}