// Find the appropriate time system correction object in the collection for the
// given time systems, and dump it to a string and return that string.
string Rinex3EphemerisStore::dumpTimeSystemCorrection(
const TimeSystem fromSys, const TimeSystem toSys) const
{
string msg;
ostringstream oss;
oss << "Convert from " << fromSys.asString()
<< " to " << toSys.asString() << " : ";
if(toSys == fromSys) {
oss << "time systems are the same";
return oss.str();
}
// look up the TimeSystemCorr in list, and dump it
map<string, TimeSystemCorrection>::const_iterator it;
for(it = mapTimeCorr.begin(); it != mapTimeCorr.end(); ++it) {
if(it->second.isConverterFor(fromSys, toSys)) {
it->second.dump(oss);
return oss.str();
}
}
oss << "conversion not found!";
return oss.str();
}
// Utility routine for getXvt and addEphemeris to convert time systems.
// Convert ttag to the target time system, using the first appropriate correction
// in the list, and return it. If no correction is found, ttag is unchanged and
// an exception is thrown.
CommonTime Rinex3EphemerisStore::correctTimeSystem(const CommonTime ttag,
const TimeSystem targetSys)
const
{
CommonTime toReturn(ttag);
TimeSystem fromSys(ttag.getTimeSystem());
// is a conversion necessary?
if(fromSys == targetSys)
return toReturn;
// first correct for leap seconds
const CivilTime civt(ttag);
double dt = TimeSystem::Correction(fromSys, targetSys,
civt.year, civt.month, civt.day);
toReturn += dt;
toReturn.setTimeSystem(targetSys);
// the corrected timetag: now only the system, not the value, matters
toReturn.setTimeSystem(targetSys);
// look up the TimeSystemCorr in list, and do the conversion
map<string, TimeSystemCorrection>::const_iterator it;
for(it = mapTimeCorr.begin(); it != mapTimeCorr.end(); ++it) {
if(it->second.isConverterFor(fromSys, targetSys)) {
dt = it->second.Correction(ttag);
toReturn += dt;
return toReturn;
}
}
// failure
InvalidRequest e("Unable to convert time systems from "
+ ttag.getTimeSystem().asString() + " to " + targetSys.asString());
GPSTK_THROW(e);
return toReturn; // never reached, satisfy some compilers
}
// Compute the conversion (in seconds) from one time system (inTS) to another
// (outTS), given the year and month of the time to be converted.
// Result is to be added to the first time (inTS) to yield the converted (outTS),
// that is t(outTS) = t(inTS) + correction(inTS,outTS).
// NB. the caller must not forget to change to outTS after adding this correction.
// @param TimeSystem inTS, input system
// @param TimeSystem outTS, output system
// @param int year, year of the time to be converted.
// @param int month, month (1-12) of the time to be converted.
// @return double dt, correction (sec) to be added to t(in) to yield t(out).
// @throw if input system(s) are invalid or Unknown.
double TimeSystem::Correction(const TimeSystem& inTS,
const TimeSystem& outTS,
const int year,
const int month,
const double day)
{
double dt(0.0);
// identity
if(inTS == outTS)
return dt;
// cannot convert unknowns
if(inTS == Unknown || outTS == Unknown) {
Exception e("Cannot compute correction for TimeSystem::Unknown");
GPSTK_THROW(e);
}
// compute TT-TDB here; ref Astronomical Almanac B7
double TDBmTT(0.0);
if(inTS == TDB || outTS == TDB) {
int iday = int(day);
long jday = convertCalendarToJD(year, month, iday) ;
double frac(day-iday);
double TJ2000(jday-2451545.5+frac); // t-J2000
// 0.0001657 sec * sin(357.53 + 0.98560028 * TJ2000 deg)
frac = ::fmod(0.017201969994578 * TJ2000, 6.2831853071796);
TDBmTT = 0.0001657 * ::sin(6.240075674 + frac);
// 0.000022 sec * sin(246.11 + 0.90251792 * TJ2000 deg)
frac = ::fmod(0.015751909262251 * TJ2000, 6.2831853071796);
TDBmTT += 0.000022 * ::sin(4.295429822 + frac);
}
// -----------------------------------------------------------
// conversions: first convert inTS->TAI ...
// TAI = GPS + 19s
// TAI = UTC + getLeapSeconds()
// TAI = TT - 32.184s
if(inTS == GPS || // GPS -> TAI
inTS == GAL) // GAL -> TAI
dt = 19.;
else if(inTS == UTC || // UTC -> TAI
inTS == BDT || // BDT -> TAI // TD is this right?
inTS == GLO) // GLO -> TAI
dt = getLeapSeconds(year, month, day);
//else if(inTS == BDT) // BDT -> TAI // RINEX 3.02 seems to say this
// dt = 34.;
else if(inTS == TAI) // TAI
;
else if(inTS == TT) // TT -> TAI
dt = -32.184;
else if(inTS == TDB) // TDB -> TAI
dt = -32.184 + TDBmTT;
else { // other
Exception e("Invalid input TimeSystem " + inTS.asString());
GPSTK_THROW(e);
}
// -----------------------------------------------------------
// ... then convert TAI->outTS
// GPS = TAI - 19s
// UTC = TAI - getLeapSeconds()
// TT = TAI + 32.184s
if(outTS == GPS || // TAI -> GPS
outTS == GAL) // TAI -> GAL
dt -= 19.;
else if(outTS == UTC || // TAI -> UTC
outTS == BDT || // TAI -> BDT
outTS == GLO) // TAI -> GLO
dt -= getLeapSeconds(year, month, day);
//else if(outTS == BDT) // TAI -> BDT
// dt -= 34.;
else if(outTS == TAI) // TAI
;
else if(outTS == TT) // TAI -> TT
dt += 32.184;
else if(outTS == TDB) // TAI -> TDB
dt += 32.184 - TDBmTT;
else if(outTS == GAL) // TD
dt = 0.0;
else { // other
Exception e("Invalid output TimeSystem " + outTS.asString());
GPSTK_THROW(e);
}
return dt;
}
