src/sct_timescales.c

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/***************************************************************************
 *   Copyright (C) 2007 by Aleksander Morgado Juez                         *
 *   scitime@aleksander_morgado.mm.st                                      *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU Library 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 Library General Public     *
 *   License along with this program; if not, write to the                 *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/

#include "scitime.h"

typedef struct _TAItoUTC_data {
    double      epochJD;            //Cols [18,26]
    double      leapSeconds;        //Cols [37,48]
    double      fact1;              //Cols [60,65]
    double      fact2;              //Cols [70,79]
} TAItoUTC_data;                    //TAI-UTC=leapSeconds+(MJD-fact1)*fact2


static const TAItoUTC_data _tai_to_utc[] = {
    { 2453736.5 ,  33.0     ,   41317.0 ,   0.0         },
    { 2451179.5 ,  32.0     ,   41317.0 ,   0.0         },
    { 2450630.5 ,  31.0     ,   41317.0 ,   0.0         },
    { 2450083.5 ,  30.0     ,   41317.0 ,   0.0         },
    { 2449534.5 ,  29.0     ,   41317.0 ,   0.0         },
    { 2449169.5 ,  28.0     ,   41317.0 ,   0.0         },
    { 2448804.5 ,  27.0     ,   41317.0 ,   0.0         },
    { 2448257.5 ,  26.0     ,   41317.0 ,   0.0         },
    { 2447892.5 ,  25.0     ,   41317.0 ,   0.0         },
    { 2447161.5 ,  24.0     ,   41317.0 ,   0.0         },
    { 2446247.5 ,  23.0     ,   41317.0 ,   0.0         },
    { 2445516.5 ,  22.0     ,   41317.0 ,   0.0         },
    { 2445151.5 ,  21.0     ,   41317.0 ,   0.0         },
    { 2444786.5 ,  20.0     ,   41317.0 ,   0.0         },
    { 2444239.5 ,  19.0     ,   41317.0 ,   0.0         },
    { 2443874.5 ,  18.0     ,   41317.0 ,   0.0         },
    { 2443509.5 ,  17.0     ,   41317.0 ,   0.0         },
    { 2443144.5 ,  16.0     ,   41317.0 ,   0.0         },
    { 2442778.5 ,  15.0     ,   41317.0 ,   0.0         },
    { 2442413.5 ,  14.0     ,   41317.0 ,   0.0         },
    { 2442048.5 ,  13.0     ,   41317.0 ,   0.0         },
    { 2441683.5 ,  12.0     ,   41317.0 ,   0.0         },
    { 2441499.5 ,  11.0     ,   41317.0 ,   0.0         },
    { 2441317.5 ,  10.0     ,   41317.0 ,   0.0         },
    { 2439887.5 ,   4.21317 ,   39126.0 ,   0.002592    },
    { 2439126.5 ,   4.31317 ,   39126.0 ,   0.002592    },
    { 2439004.5 ,   3.84013 ,   38761.0 ,   0.001296    },
    { 2438942.5 ,   3.74013 ,   38761.0 ,   0.001296    },
    { 2438820.5 ,   3.64013 ,   38761.0 ,   0.001296    },
    { 2438761.5 ,   3.54013 ,   38761.0 ,   0.001296    },
    { 2438639.5 ,   3.44013 ,   38761.0 ,   0.001296    },
    { 2438486.5 ,   3.34013 ,   38761.0 ,   0.001296    },
    { 2438395.5 ,   3.24013 ,   38761.0 ,   0.001296    },
    { 2438334.5 ,   1.945858,   37665.0 ,   0.0011232   },
    { 2437665.5 ,   1.845858,   37665.0 ,   0.0011232   },
    { 2437512.5 ,   1.372818,   37300.0 ,   0.001296    },
    { 2437300.5 ,   1.422818,   37300.0 ,   0.001296    },
    { NAN       ,   0.0     ,       0.0,    0.0         }
};

static double _sct_get_leapseconds_from_epoch(sct_time_ptr pElem);


SCT_TIMESCALE sct_get_timescale (sct_time_ptr pElem)
{
    return pElem->timescale;
}

SCT_RET sct_set_timescale (sct_time_ptr pElem, SCT_TIMESCALE timescale)
{
    pElem->timescale = timescale;
    return  SCT_RET_OK;
}

SCT_RET sct_from_TAI_to_UTC (sct_time_ptr pElem)
{
    double leapseconds;
    sct_time delta;
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_TAI)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from TAI to"
            "UTC a time element which is NOT TAI.\n", __FUNCTION__);
    }
    #endif

    //Get leapseconds for this epoch...
    leapseconds = _sct_get_leapseconds_from_epoch(pElem);
    if(isnan(leapseconds))
    {
        return SCT_RET_INVALID_LEAPSECONDS;
    }
    leapseconds *= (-1.0);

    //Set seconds in delta element...
    sct_set_delta_secs(&delta,leapseconds);

    //Add delta to output element
    sct_add_delta(pElem,pElem,&delta);

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_UTC;

    return SCT_RET_OK;
}


SCT_RET sct_from_TAI_to_GPS (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_TAI)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from TAI to"
            "GPS a time element which is NOT TAI.\n", __FUNCTION__);
    }
    #endif

    //The difference between TAI and GPS is always SCT_GPS_TAI_LEAPSECOND
    // (GPS is behind TAI)
    sct_add_deltaDSF(pElem,pElem,0,-SCT_GPS_TAI_LEAPSECOND,0);

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_GPS;

    return SCT_RET_OK;
}


SCT_RET sct_from_TAI_to_UT (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_TAI)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from TAI to"
            "UT a time element which is NOT TAI.\n", __FUNCTION__);
    }
    #endif

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_UT;

    return SCT_RET_OK;
}


SCT_RET sct_from_UTC_to_TAI (sct_time_ptr pElem)
{
    double leapseconds;
    sct_time delta;

    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_UTC)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from UTC to"
            "TAI a time element which is NOT UTC.\n", __FUNCTION__);
    }
    #endif

    //Get leapseconds for this epoch...
    leapseconds = _sct_get_leapseconds_from_epoch(pElem);
    if(isnan(leapseconds))
    {
        return SCT_RET_INVALID_LEAPSECONDS;
    }

    //Set seconds in delta element...
    sct_set_delta_secs(&delta,leapseconds);

    //Add delta to output element
    sct_add_delta(pElem,pElem,&delta);

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_TAI;

    return SCT_RET_OK;
}


SCT_RET sct_from_UTC_to_GPS (sct_time_ptr pElem)
{
    double leapseconds;
    sct_time delta;

    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_UTC)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from UTC to"
            "GPS a time element which is NOT UTC.\n", __FUNCTION__);
    }
    #endif

    //Get leapseconds for this epoch...
    leapseconds = _sct_get_leapseconds_from_epoch(pElem);
    if(isnan(leapseconds))
    {
        return SCT_RET_INVALID_LEAPSECONDS;
    }

    //Set seconds in delta element... 
    sct_set_delta_secs(&delta,leapseconds);

    //Add delta to output element (so converting to TAI)
    sct_add_delta(pElem,pElem,&delta);

    //The difference between TAI and GPS is always SCT_GPS_TAI_LEAPSECOND
    // (GPS is behind TAI)
    sct_add_deltaDSF(pElem,pElem,0,-SCT_GPS_TAI_LEAPSECOND,0);

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_GPS;

    return SCT_RET_OK;
}


SCT_RET sct_from_UTC_to_UT (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_UTC)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from UTC to"
            "UT a time element which is NOT UTC.\n", __FUNCTION__);
    }
    #endif

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_UT;

    return SCT_RET_OK;
}


SCT_RET sct_from_GPS_to_TAI (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_GPS)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from GPS to"
            "TAI a time element which is NOT GPS.\n", __FUNCTION__);
    }
    #endif

    //The difference between TAI and GPS is always SCT_GPS_TAI_LEAPSECOND
    // (GPS is behind TAI)
    sct_add_deltaDSF(pElem,pElem,0,SCT_GPS_TAI_LEAPSECOND,0);

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_TAI;

    return SCT_RET_OK;
}


SCT_RET sct_from_GPS_to_UTC (sct_time_ptr pElem)
{
    double leapseconds;
    sct_time delta;

    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_GPS)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from GPS to"
            "UTC a time element which is NOT GPS.\n", __FUNCTION__);
    }
    #endif

    //The difference between TAI and GPS is always SCT_GPS_TAI_LEAPSECOND
    // (GPS is behind TAI)... so converting to TAI
    sct_add_deltaDSF(pElem,pElem,0,SCT_GPS_TAI_LEAPSECOND,0);

    //Get leapseconds for this epoch...
    leapseconds = _sct_get_leapseconds_from_epoch(pElem);
    if(isnan(leapseconds))
    {
        return SCT_RET_INVALID_LEAPSECONDS;
    }
    leapseconds *= (-1.0);

    //Set seconds in delta element...
    sct_set_delta_secs(&delta,leapseconds);

    //Add delta to output element (so converting to UTC)
    sct_add_delta(pElem,pElem,&delta);

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_UTC;

    return SCT_RET_OK;
}


SCT_RET sct_from_GPS_to_UT (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_GPS)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from GPS to"
            "UT a time element which is NOT GPS.\n", __FUNCTION__);
    }
    #endif

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_UT;

    return SCT_RET_OK;
}


SCT_RET sct_from_UT_to_TAI (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_UT)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from UT to"
            "TAI a time element which is NOT UT.\n", __FUNCTION__);
    }
    #endif

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_TAI;

    return SCT_RET_OK;
}


SCT_RET sct_from_UT_to_GPS (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_UT)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from UT to"
            "GPS a time element which is NOT UT.\n", __FUNCTION__);
    }
    #endif

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_GPS;

    return SCT_RET_OK;
}


SCT_RET sct_from_UT_to_UTC (sct_time_ptr pElem)
{
    #ifdef SCT_DEBUG
    if(pElem->timescale != SCT_TIMESCALE_UT)
    {
        fprintf(stderr, "[scitime:%s] >> Warning! Trying to convert from UT to"
            "UTC a time element which is NOT UT.\n", __FUNCTION__);
    }
    #endif

    //Set final timescale
    pElem->timescale = SCT_TIMESCALE_UTC;

    return SCT_RET_OK;
}


static double _sct_get_leapseconds_from_epoch(sct_time_ptr pElem)
{
    extern const TAItoUTC_data _tai_to_utc[];
    int ind = 0;
    double elementJD;

    //Get JD epoch...
    sct_get_jd(pElem,&elementJD);

    //Loop the TAI-UTC data...
    while(!isnan(_tai_to_utc[ind].epochJD))
    {
        //Compare epochs...
        if(elementJD > _tai_to_utc[ind].epochJD)
        {
            //Ok, get leapseconds for this epoch...
            if(_tai_to_utc[ind].fact2 == 0.0)
                return _tai_to_utc[ind].leapSeconds;
            else
            {
                double elementMJD;
                sct_get_mjd(pElem,&elementMJD);
                return ( _tai_to_utc[ind].leapSeconds + \
                         (elementMJD - _tai_to_utc[ind].fact1) * \
                         _tai_to_utc[ind].fact2);
            }
        }
        //Update index...
        ind++;
    }

    return NAN;
}

---