void RadioTap::init() {
channel(Utils::channel_to_mhz(1), 0xa0);
flags(FCS);
tsft(0);
dbm_signal(0xce);
rx_flags(0);
antenna(0);
}
/* Compute the value of satellite antenna phase correction, in meters.
* @param satid Satellite ID
* @param time Epoch of interest
* @param satpos Satellite position, as a Triple
* @param sunpos Sun position, as a Triple
*
* @return Satellite antenna phase correction, in meters.
*/
double ComputeSatPCenter::getSatPCenter( const SatID& satid,
const DayTime& time,
const Triple& satpos,
const Triple& sunPosition )
{
// Unitary vector from satellite to Earth mass center (ECEF)
Triple rk( ( (-1.0)*(satpos.unitVector()) ) );
// Unitary vector from Earth mass center to Sun (ECEF)
Triple ri( sunPosition.unitVector() );
// rj = rk x ri: Rotation axis of solar panels (ECEF)
Triple rj(rk.cross(ri));
// Redefine ri: ri = rj x rk (ECEF)
ri = rj.cross(rk);
// Let's convert ri to an unitary vector. (ECEF)
ri = ri.unitVector();
// Get vector from Earth mass center to receiver
Triple rxPos(nominalPos.X(), nominalPos.Y(), nominalPos.Z());
// Compute unitary vector vector from satellite to RECEIVER
Triple rrho( (rxPos-satpos).unitVector() );
// When not using Antex information, if satellite belongs to block
// "IIR" its correction is 0.0, else it will depend on satellite model.
// This variable that will hold the correction, 0.0 by default
double svPCcorr(0.0);
// Check is Antex antenna information is available or not, and if
// available, whether satellite phase center information is absolute
// or relative
bool absoluteModel( false );
if( pAntexReader != NULL )
{
absoluteModel = pAntexReader->isAbsolute();
}
if( absoluteModel )
{
// We will need the elevation, in degrees. It is found using
// dot product and the corresponding unitary angles
double elev( 90.0 - (std::acos( rrho.dot(rk) ) * RAD_TO_DEG) );
// Get satellite information in Antex format. Currently this
// only works for GPS and Glonass.
if( satid.system == SatID::systemGPS )
{
std::stringstream sat;
sat << "G";
if( satid.id < 10 )
{
sat << "0";
}
sat << satid.id;
// Get satellite antenna information out of AntexReader object
Antenna antenna( pAntexReader->getAntenna( sat.str(), time ) );
// Get antenna eccentricity for frequency "G01" (L1), in
// satellite reference system.
// NOTE: It is NOT in ECEF, it is in UEN!!!
Triple satAnt( antenna.getAntennaEccentricity( Antenna::G01) );
// Now, get the phase center variation.
Triple var( antenna.getAntennaPCVariation( Antenna::G01, elev) );
// We must substract them
satAnt = satAnt - var;
// Change to ECEF
Triple svAntenna( satAnt[2]*ri + satAnt[1]*rj + satAnt[0]*rk );
// Projection of "svAntenna" vector to line of sight vector rrho
svPCcorr = (rrho.dot(svAntenna));
}
else
{
// Check if this satellite belongs to Glonass system
if( satid.system == SatID::systemGlonass )
{
std::stringstream sat;
sat << "R";
if( satid.id < 10 )
{
sat << "0";
}
sat << satid.id;
// Get satellite antenna information out of AntexReader object
Antenna antenna( pAntexReader->getAntenna( sat.str(), time ) );
// Get antenna offset for frequency "R01" (Glonass), in
// satellite reference system.
// NOTE: It is NOT in ECEF, it is in UEN!!!
Triple satAnt( antenna.getAntennaEccentricity( Antenna::R01) );
// Now, get the phase center variation.
Triple var( antenna.getAntennaPCVariation( Antenna::R01, elev) );
// We must substract them
satAnt = satAnt - var;
// Change to ECEF
Triple svAntenna( satAnt[2]*ri + satAnt[1]*rj + satAnt[0]*rk );
// Project "svAntenna" vector to line of sight vector rrho
svPCcorr = (rrho.dot(svAntenna));
}
else
{
// In this case no correction will be computed
svPCcorr = 0.0;
}
} // End of 'if( satid.system == SatID::systemGPS )...'
}
else
{
// If no Antex information is given, or if phase center information
// uses a relative model, then use a simpler, older approach
// Please note that in this case all GLONASS satellite are
// considered as having phase center at (0.0, 0.0, 0.0). The former
// is not true for 'GLONASS-M' satellites (-0.545, 0.0, 0.0 ), but
// currently there is no simple way to take this into account.
// For satellites II and IIA:
if( (satData.getBlock( satid, time ) == "II") ||
(satData.getBlock( satid, time ) == "IIA") )
{
// First, build satellite antenna vector for models II/IIA
Triple svAntenna(0.279*ri + 1.023*rk);
// Projection of "svAntenna" vector to line of sight vector rrho
svPCcorr = (rrho.dot(svAntenna));
}
else
{
// For satellites belonging to block "I"
if( (satData.getBlock( satid, time ) == "I") )
{
// First, build satellite antenna vector for model I
Triple svAntenna(0.210*ri + 0.854*rk);
// Projection of "svAntenna" to line of sight vector (rrho)
svPCcorr = (rrho.dot(svAntenna));
}
} // End of 'if( (satData.getBlock( satid, time ) == "II") ||...'
} // End of 'if( absoluteModel )...'
// This correction is interpreted as an "advance" in the signal,
// instead of a delay. Therefore, it has negative sign
return (-svPCcorr);
} // End of method 'ComputeSatPCenter::getSatPCenter()'
