source: ntrip/trunk/BNC/src/combination/bnccomb.cpp@ 4281

/* -------------------------------------------------------------------------
 * BKG NTRIP Client
 * -------------------------------------------------------------------------
 *
 * Class:      bncComb
 *
 * Purpose:    Combinations of Orbit/Clock Corrections
 *
 * Author:     L. Mervart
 *
 * Created:    22-Jan-2011
 *
 * Changes:    
 *
 * -----------------------------------------------------------------------*/

#include <newmatio.h>
#include <iomanip>
#include <sstream>

#include "bnccomb.h"
#include "bncapp.h"
#include "upload/bncrtnetdecoder.h"
#include "bncsettings.h"
#include "bncmodel.h"
#include "bncutils.h"
#include "bncpppclient.h"
#include "bncsp3.h"
#include "bncantex.h"
#include "bnctides.h"

const double sig0_offAC    = 1000.0;
const double sig0_offACSat =  100.0;
const double sigP_offACSat =   0.01;
const double sig0_clkSat   =  100.0;

const double sigObs        =   0.05;

const int MAXPRN_GPS     = 32;
const int MAXPRN_GLONASS = 24;

using namespace std;

// Constructor
////////////////////////////////////////////////////////////////////////////
cmbParam::cmbParam(parType type_, int index_,
                   const QString& ac_, const QString& prn_) {

  type   = type_;
  index  = index_;
  AC     = ac_;
  prn    = prn_;
  xx     = 0.0;
  eph    = 0;

  if      (type == offACgps) {
    epoSpec = true;
    sig0    = sig0_offAC;
    sigP    = sig0;
  }
  else if (type == offACglo) {
    epoSpec = true;
    sig0    = sig0_offAC;
    sigP    = sig0;
  }
  else if (type == offACSat) {
    epoSpec = false;
    sig0    = sig0_offACSat;
    sigP    = sigP_offACSat;
  }
  else if (type == clkSat) {
    epoSpec = true;
    sig0    = sig0_clkSat;
    sigP    = sig0;
  }
}

// Destructor
////////////////////////////////////////////////////////////////////////////
cmbParam::~cmbParam() {
}

// Partial
////////////////////////////////////////////////////////////////////////////
double cmbParam::partial(const QString& AC_, const QString& prn_) {
  
  if      (type == offACgps) {
    if (AC == AC_ && prn_[0] == 'G') {
      return 1.0;
    }
  }
  else if (type == offACglo) {
    if (AC == AC_ && prn_[0] == 'R') {
      return 1.0;
    }
  }
  else if (type == offACSat) {
    if (AC == AC_ && prn == prn_) {
      return 1.0;
    }
  }
  else if (type == clkSat) {
    if (prn == prn_) {
      return 1.0;
    }
  }

  return 0.0;
}

// 
////////////////////////////////////////////////////////////////////////////
QString cmbParam::toString() const {

  QString outStr;
 
  if      (type == offACgps) {
    outStr = "AC offset GPS " + AC;
  }
  else if (type == offACglo) {
    outStr = "AC offset GLO " + AC;
  }
  else if (type == offACSat) {
    outStr = "Sat Offset " + AC + " " + prn;
  }
  else if (type == clkSat) {
    outStr = "Clk Corr " + prn;
  }

  return outStr;
}

// Constructor
////////////////////////////////////////////////////////////////////////////
bncComb::bncComb() {

  bncSettings settings;

  QStringList combineStreams = settings.value("combineStreams").toStringList();

  _cmbSampl = settings.value("cmbSampl").toInt();
  if (_cmbSampl <= 0) {
    _cmbSampl = 10;
  }

  _masterMissingEpochs = 0;

  if (combineStreams.size() >= 1 && !combineStreams[0].isEmpty()) {
    QListIterator<QString> it(combineStreams);
    while (it.hasNext()) {
      QStringList hlp = it.next().split(" ");
      cmbAC* newAC = new cmbAC();
      newAC->mountPoint = hlp[0];
      newAC->name       = hlp[1];
      newAC->weight     = hlp[2].toDouble();
      if (_masterOrbitAC.isEmpty()) {
        _masterOrbitAC = newAC->name;
      }
      _ACs.append(newAC);
    }
  }

  _rtnetDecoder = 0;

  connect(this, SIGNAL(newMessage(QByteArray,bool)), 
          ((bncApp*)qApp), SLOT(slotMessage(const QByteArray,bool)));

  // Combination Method
  // ------------------
  if (settings.value("cmbMethod").toString() == "Single-Epoch") {
    _method = singleEpoch;
  }
  else {
    _method = filter;
  }

  // Use Glonass
  // -----------
  if ( Qt::CheckState(settings.value("pppGLONASS").toInt()) == Qt::Checked) {
    _useGlonass = true;
  }
  else {
    _useGlonass = false;
  }

  // Initialize Parameters (model: Clk_Corr = AC_Offset + Sat_Offset + Clk)
  // ----------------------------------------------------------------------
  if (_method == filter) {
    int nextPar = 0;
    QListIterator<cmbAC*> it(_ACs);
    while (it.hasNext()) {
      cmbAC* AC = it.next();
      _params.push_back(new cmbParam(cmbParam::offACgps, ++nextPar, AC->name, ""));
      for (int iGps = 1; iGps <= MAXPRN_GPS; iGps++) {
        QString prn = QString("G%1").arg(iGps, 2, 10, QChar('0'));
        _params.push_back(new cmbParam(cmbParam::offACSat, ++nextPar, 
                                       AC->name, prn));
      }
      if (_useGlonass) {
        _params.push_back(new cmbParam(cmbParam::offACglo, ++nextPar, AC->name, ""));
        for (int iGlo = 1; iGlo <= MAXPRN_GLONASS; iGlo++) {
          QString prn = QString("R%1").arg(iGlo, 2, 10, QChar('0'));
          _params.push_back(new cmbParam(cmbParam::offACSat, ++nextPar, 
                                         AC->name, prn));
        }
      }
    }
    for (int iGps = 1; iGps <= MAXPRN_GPS; iGps++) {
      QString prn = QString("G%1").arg(iGps, 2, 10, QChar('0'));
      _params.push_back(new cmbParam(cmbParam::clkSat, ++nextPar, "", prn));
    }
    if (_useGlonass) {
      for (int iGlo = 1; iGlo <= MAXPRN_GLONASS; iGlo++) {
        QString prn = QString("R%1").arg(iGlo, 2, 10, QChar('0'));
        _params.push_back(new cmbParam(cmbParam::clkSat, ++nextPar, "", prn));
      }
    }
    
    // Initialize Variance-Covariance Matrix
    // -------------------------------------
    _QQ.ReSize(_params.size());
    _QQ = 0.0;
    for (int iPar = 1; iPar <= _params.size(); iPar++) {
      cmbParam* pp = _params[iPar-1];
      _QQ(iPar,iPar) = pp->sig0 * pp->sig0;
    }
  }

  // ANTEX File
  // ----------
  _antex = 0;
  QString antexFileName = settings.value("pppAntex").toString();
  if (!antexFileName.isEmpty()) {
    _antex = new bncAntex();
    if (_antex->readFile(antexFileName) != success) {
      emit newMessage("wrong ANTEX file", true);
      delete _antex;
      _antex = 0;
    }
  }

  // Maximal Residuum
  // ----------------
  _MAXRES = settings.value("cmbMaxres").toDouble();
  if (_MAXRES <= 0.0) {
    _MAXRES = 999.0;
  }
}

// Destructor
////////////////////////////////////////////////////////////////////////////
bncComb::~bncComb() {
  QListIterator<cmbAC*> icAC(_ACs);
  while (icAC.hasNext()) {
    delete icAC.next();
  }
  delete _rtnetDecoder;
  delete _antex;
  for (int iPar = 1; iPar <= _params.size(); iPar++) {
    delete _params[iPar-1];
  }
  QListIterator<bncTime> itTime(_buffer.keys());
  while (itTime.hasNext()) {
    bncTime epoTime = itTime.next();
    _buffer.remove(epoTime);
  }
  QMapIterator<QString, cmbCorr*> itOrbCorr(_orbitCorrs);
  while (itOrbCorr.hasNext()) {
    itOrbCorr.next();
    delete itOrbCorr.value();
  }
}

// Read and store one correction line
////////////////////////////////////////////////////////////////////////////
void bncComb::processCorrLine(const QString& staID, const QString& line) {
  QMutexLocker locker(&_mutex);

  // Find the AC Name
  // ----------------
  QString acName;
  QListIterator<cmbAC*> icAC(_ACs);
  while (icAC.hasNext()) {
    cmbAC* AC = icAC.next();
    if (AC->mountPoint == staID) {
      acName = AC->name;
      break;
    }
  }
  if (acName.isEmpty()) {
    return;
  }

  // Read the Correction
  // -------------------
  cmbCorr* newCorr = new cmbCorr();
  newCorr->acName = acName;
  if (!newCorr->readLine(line) == success) {
    delete newCorr;
    return;
  }

  // Check Glonass
  // -------------
  if (!_useGlonass) {
    if (newCorr->prn[0] == 'R') {
      delete newCorr;
      return;
    }
  }

  // Save Orbit-Only Corrections
  // ---------------------------
  if (newCorr->tRao.valid() && !newCorr->tClk.valid()) {
    QString corrID = newCorr->ID();
    if (_orbitCorrs.find(corrID) != _orbitCorrs.end()) {
      delete _orbitCorrs[corrID];
    }
    _orbitCorrs[corrID] = newCorr;
    return;
  }

  // Merge with saved orbit correction
  // ---------------------------------
  else if (newCorr->tClk.valid() && !newCorr->tRao.valid()) {
    QString corrID = newCorr->ID();
    if (_orbitCorrs.find(corrID) != _orbitCorrs.end()) {
      mergeOrbitCorr(_orbitCorrs[corrID], newCorr);
    }
  }

  // Check Modulo Time
  // -----------------
  if (int(newCorr->tClk.gpssec()) % _cmbSampl != 0.0) {
    delete newCorr;
    return;
  }

  // Delete old corrections
  // ----------------------
  if (_resTime.valid() && newCorr->tClk <= _resTime) {
    delete newCorr;
    return;
  }

  // Check the Ephemeris
  //--------------------
  if (_eph.find(newCorr->prn) == _eph.end()) {
    delete newCorr;
    return;
  }
  else {
    t_eph* lastEph = _eph[newCorr->prn]->last;
    t_eph* prevEph = _eph[newCorr->prn]->prev;
    if      (lastEph && lastEph->IOD() == newCorr->iod) {
      newCorr->eph = lastEph;
    }
    else if (lastEph && prevEph && prevEph->IOD() == newCorr->iod) {
      newCorr->eph = prevEph;
      switchToLastEph(lastEph, newCorr);
    }
    else {
      delete newCorr;
      return;
    }
  }

  // Process previous Epoch(s)
  // -------------------------
  QListIterator<bncTime> itTime(_buffer.keys());
  while (itTime.hasNext()) {
    bncTime epoTime = itTime.next();
    if (epoTime < newCorr->tClk - _cmbSampl) {
      _resTime = epoTime;
      processEpoch();
    }
  }

  // Merge or add the correction
  // ---------------------------
  QVector<cmbCorr*>& corrs = _buffer[newCorr->tClk].corrs;
  cmbCorr* existingCorr = 0;
  QVectorIterator<cmbCorr*> itCorr(corrs);
  while (itCorr.hasNext()) {
    cmbCorr* hlp = itCorr.next();
    if (hlp->prn == newCorr->prn && hlp->acName == newCorr->acName) {
      existingCorr = hlp;
      break;
    }
  }
  if (existingCorr) {
    delete newCorr; newCorr = 0;
    existingCorr->readLine(line); // merge (multiple messages)
   
  }
  else {
    corrs.append(newCorr);
  }
}

// Change the correction so that it refers to last received ephemeris 
////////////////////////////////////////////////////////////////////////////
void bncComb::switchToLastEph(const t_eph* lastEph, t_corr* corr) {

  if (corr->eph == lastEph) {
    return;
  }

  ColumnVector oldXC(4);
  ColumnVector oldVV(3);
  corr->eph->position(corr->tRao.gpsw(), corr->tRao.gpssec(), 
                      oldXC.data(), oldVV.data());

  ColumnVector newXC(4);
  ColumnVector newVV(3);
  lastEph->position(corr->tRao.gpsw(), corr->tRao.gpssec(), 
                    newXC.data(), newVV.data());

  ColumnVector dX = newXC.Rows(1,3) - oldXC.Rows(1,3);
  ColumnVector dV = newVV           - oldVV;
  double       dC = newXC(4)        - oldXC(4);

  ColumnVector dRAO(3);
  XYZ_to_RSW(newXC.Rows(1,3), newVV, dX, dRAO);

  ColumnVector dDotRAO(3);
  XYZ_to_RSW(newXC.Rows(1,3), newVV, dV, dDotRAO);

  QString msg = "switch corr " + corr->prn 
    + QString(" %1 -> %2 %3").arg(corr->iod,3)
    .arg(lastEph->IOD(),3).arg(dC*t_CST::c, 8, 'f', 4);

  emit newMessage(msg.toAscii(), false);

  corr->iod     = lastEph->IOD();
  corr->eph     = lastEph;
  corr->rao    += dRAO;
  corr->dotRao += dDotRAO;
  corr->dClk   -= dC;
}

// Process Epoch
////////////////////////////////////////////////////////////////////////////
void bncComb::processEpoch() {

  _log.clear();

  QTextStream out(&_log, QIODevice::WriteOnly);

  out << endl <<           "Combination:" << endl 
      << "------------------------------" << endl;

  // Observation Statistics
  // ----------------------
  bool masterPresent = false;
  QListIterator<cmbAC*> icAC(_ACs);
  while (icAC.hasNext()) {
    cmbAC* AC = icAC.next();
    AC->numObs = 0;
    QVectorIterator<cmbCorr*> itCorr(corrs());
    while (itCorr.hasNext()) {
      cmbCorr* corr = itCorr.next();
      if (corr->acName == AC->name) {
        AC->numObs += 1;
        if (AC->name == _masterOrbitAC) {
          masterPresent = true;
        }
      }
    }
    out << AC->name.toAscii().data() << ": " << AC->numObs << endl;
  }

  // If Master not present, switch to another one
  // --------------------------------------------
  if (masterPresent) {
    _masterMissingEpochs = 0;
  }
  else {
    ++_masterMissingEpochs;
    if (_masterMissingEpochs < 10) {
      out << "Missing Master, Epoch skipped" << endl;
      _buffer.remove(_resTime);
      emit newMessage(_log, false);
      return;
    }
    else {
      _masterMissingEpochs = 0;
      QListIterator<cmbAC*> icAC(_ACs);
      while (icAC.hasNext()) {
        cmbAC* AC = icAC.next();
        if (AC->numObs > 0) {
          out << "Switching Master AC "
              << _masterOrbitAC.toAscii().data() << " --> " 
              << AC->name.toAscii().data()   << " " 
              << _resTime.datestr().c_str()    << " " 
              << _resTime.timestr().c_str()    << endl;
          _masterOrbitAC = AC->name;
          break;
        }
      }
    }
  }

  QMap<QString, t_corr*> resCorr;

  // Perform the actual Combination using selected Method
  // ----------------------------------------------------
  t_irc irc;
  ColumnVector dx;
  if (_method == filter) {
    irc = processEpoch_filter(out, resCorr, dx);
  }
  else {
    irc = processEpoch_singleEpoch(out, resCorr, dx);
  }

  // Update Parameter Values, Print Results
  // --------------------------------------
  if (irc == success) {
    for (int iPar = 1; iPar <= _params.size(); iPar++) {
      cmbParam* pp = _params[iPar-1];
      pp->xx += dx(iPar);
      if (pp->type == cmbParam::clkSat) {
        if (resCorr.find(pp->prn) != resCorr.end()) {
          resCorr[pp->prn]->dClk = pp->xx / t_CST::c;
        }
      }
      out << _resTime.datestr().c_str() << " " 
          << _resTime.timestr().c_str() << " ";
      out.setRealNumberNotation(QTextStream::FixedNotation);
      out.setFieldWidth(8);
      out.setRealNumberPrecision(4);
      out << pp->toString() << " "
          << pp->xx << " +- " << sqrt(_QQ(pp->index,pp->index)) << endl;
      out.setFieldWidth(0);
    }
    printResults(out, resCorr);
    dumpResults(resCorr);
  }

  // Delete Data, emit Message
  // -------------------------
  _buffer.remove(_resTime);
  emit newMessage(_log, false);
}

// Process Epoch - Filter Method
////////////////////////////////////////////////////////////////////////////
t_irc bncComb::processEpoch_filter(QTextStream& out,
                                   QMap<QString, t_corr*>& resCorr,
                                   ColumnVector& dx) {

  // Prediction Step
  // ---------------
  int nPar = _params.size();
  ColumnVector x0(nPar);
  for (int iPar = 1; iPar <= _params.size(); iPar++) {
    cmbParam* pp  = _params[iPar-1];
    if (pp->epoSpec) {
      pp->xx = 0.0;
      _QQ.Row(iPar)    = 0.0;
      _QQ.Column(iPar) = 0.0;
      _QQ(iPar,iPar) = pp->sig0 * pp->sig0;
    }
    else {
      _QQ(iPar,iPar) += pp->sigP * pp->sigP;
    }
    x0(iPar) = pp->xx;
  }

  // Check Satellite Positions for Outliers
  // --------------------------------------
  if (checkOrbits(out) != success) {
    return failure;
  }

  // Update and outlier detection loop
  // ---------------------------------
  SymmetricMatrix QQ_sav = _QQ;
  while (true) {

    Matrix         AA;
    ColumnVector   ll;
    DiagonalMatrix PP;

    if (createAmat(AA, ll, PP, x0, resCorr) != success) {
      return failure;
    }

    bncModel::kalman(AA, ll, PP, _QQ, dx);
    ColumnVector vv = ll - AA * dx;

    int     maxResIndex;
    double  maxRes = vv.maximum_absolute_value1(maxResIndex);   
    out.setRealNumberNotation(QTextStream::FixedNotation);
    out.setRealNumberPrecision(3);  
    out << _resTime.datestr().c_str() << " " << _resTime.timestr().c_str()
        << " Maximum Residuum " << maxRes << ' '
        << corrs()[maxResIndex-1]->acName << ' ' << corrs()[maxResIndex-1]->prn;

    if (maxRes > _MAXRES) {
      for (int iPar = 1; iPar <= _params.size(); iPar++) {
        cmbParam* pp = _params[iPar-1];
        if (pp->type == cmbParam::offACSat            && 
            pp->AC   == corrs()[maxResIndex-1]->acName &&
            pp->prn  == corrs()[maxResIndex-1]->prn) { 
          QQ_sav.Row(iPar)    = 0.0;
          QQ_sav.Column(iPar) = 0.0;
          QQ_sav(iPar,iPar)   = pp->sig0 * pp->sig0;
        }
      }

      out << "  Outlier" << endl;
      _QQ = QQ_sav;
      corrs().remove(maxResIndex-1);
    }
    else {
      out << "  OK" << endl;
      break;
    }
  }

  return success;
}

// Print results
////////////////////////////////////////////////////////////////////////////
void bncComb::printResults(QTextStream& out,
                           const QMap<QString, t_corr*>& resCorr) {

  QMapIterator<QString, t_corr*> it(resCorr);
  while (it.hasNext()) {
    it.next();
    t_corr* corr = it.value();
    const t_eph* eph = corr->eph;
    if (eph) {
      double xx, yy, zz, cc;
      eph->position(_resTime.gpsw(), _resTime.gpssec(), xx, yy, zz, cc);

      out << _resTime.datestr().c_str() << " " 
          << _resTime.timestr().c_str() << " ";
      out.setFieldWidth(3);
      out << "Full Clock " << corr->prn << " " << corr->iod << " ";
      out.setFieldWidth(14);
      out << (cc + corr->dClk) * t_CST::c << endl;
      out.setFieldWidth(0);
    }
    else {
      out << "bncComb::printResuls bug" << endl;
    }
  }
}

// Send results to RTNet Decoder and directly to PPP Client
////////////////////////////////////////////////////////////////////////////
void bncComb::dumpResults(const QMap<QString, t_corr*>& resCorr) {

  ostringstream out; out.setf(std::ios::fixed);
  QStringList   corrLines;

  unsigned year, month, day, hour, minute;
  double   sec;
  _resTime.civil_date(year, month, day);
  _resTime.civil_time(hour, minute, sec);

  out << "*  " 
      << setw(4)  << year   << " " 
      << setw(2)  << month  << " " 
      << setw(2)  << day    << " " 
      << setw(2)  << hour   << " " 
      << setw(2)  << minute << " " 
      << setw(12) << setprecision(8) << sec << " "
      << endl; 

  QMapIterator<QString, t_corr*> it(resCorr);
  while (it.hasNext()) {
    it.next();
    t_corr* corr = it.value();

    double dT = 60.0;

    for (int iTime = 1; iTime <= 2; iTime++) {

      bncTime time12 = (iTime == 1) ? _resTime : _resTime + dT;

      ColumnVector xc(4);
      ColumnVector vv(3);
      corr->eph->position(time12.gpsw(), time12.gpssec(), 
                          xc.data(), vv.data());
      bncPPPclient::applyCorr(time12, corr, xc, vv);
      
      // Relativistic Correction
      // -----------------------
      double relCorr = - 2.0 * DotProduct(xc.Rows(1,3),vv) / t_CST::c / t_CST::c;
      xc(4) -= relCorr;
      
      // Code Biases
      // -----------
      double dcbP1C1 = 0.0;
      double dcbP1P2 = 0.0;
      
      // Correction Phase Center --> CoM
      // -------------------------------
      ColumnVector dx(3); dx = 0.0;
      if (_antex) {
        double Mjd = time12.mjd() + time12.daysec()/86400.0;
        if (_antex->satCoMcorrection(corr->prn, Mjd, xc.Rows(1,3), dx) == success) {
          xc(1) -= dx(1);
          xc(2) -= dx(2);
          xc(3) -= dx(3);
        }
        else {
          cout << "antenna not found" << endl;
        }
      }
      
      if (iTime == 1) {
        out << 'P' << corr->prn.toAscii().data()
            << setw(14) << setprecision(6) << xc(1) / 1000.0
            << setw(14) << setprecision(6) << xc(2) / 1000.0
            << setw(14) << setprecision(6) << xc(3) / 1000.0
            << setw(14) << setprecision(6) << xc(4) * 1e6
            << setw(14) << setprecision(6) << relCorr * 1e6
            << setw(8)  << setprecision(3) << dx(1)
            << setw(8)  << setprecision(3) << dx(2)
            << setw(8)  << setprecision(3) << dx(3)
            << setw(8)  << setprecision(3) << dcbP1C1
            << setw(8)  << setprecision(3) << dcbP1P2
            << setw(6)  << setprecision(1) << dT;

        QString line;
        int messageType = COTYPE_GPSCOMBINED;
        int updateInt   = 0;
        line.sprintf("%d %d %d %.1f %s"
                     "   %3d"
                     "   %8.3f %8.3f %8.3f %8.3f"
                     "   %10.5f %10.5f %10.5f %10.5f"
                     "   %10.5f  %10.5f %10.5f %10.5f INTERNAL",
                     messageType, updateInt, time12.gpsw(), time12.gpssec(),
                     corr->prn.toAscii().data(),
                     corr->iod,
                     corr->dClk * t_CST::c,
                     corr->rao[0],
                     corr->rao[1],
                     corr->rao[2],
                     corr->dotDClk * t_CST::c,
                     corr->dotRao[0],
                     corr->dotRao[1],
                     corr->dotRao[2],
                     corr->dotDotDClk * t_CST::c,
                     corr->dotDotRao[0],
                     corr->dotDotRao[1],
                     corr->dotDotRao[2]);
        corrLines << line;
      }
      else {
        out << setw(14) << setprecision(6) << xc(1) / 1000.0
            << setw(14) << setprecision(6) << xc(2) / 1000.0
            << setw(14) << setprecision(6) << xc(3) / 1000.0 << endl;
      }
    }

    delete corr;
  }
  out << "EOE" << endl; // End Of Epoch flag

  if (!_rtnetDecoder) {
    _rtnetDecoder = new bncRtnetDecoder();
  }

  vector<string> errmsg;
  _rtnetDecoder->Decode((char*) out.str().data(), out.str().size(), errmsg);

  // Optionally send new Corrections to PPP
  // --------------------------------------
  bncApp* app = (bncApp*) qApp;
  if (app->_bncPPPclient) {
    app->_bncPPPclient->slotNewCorrections(corrLines);
  }
}

// Create First Design Matrix and Vector of Measurements
////////////////////////////////////////////////////////////////////////////
t_irc bncComb::createAmat(Matrix& AA, ColumnVector& ll, DiagonalMatrix& PP,
                          const ColumnVector& x0, 
                          QMap<QString, t_corr*>& resCorr) {

  unsigned nPar = _params.size();
  unsigned nObs = corrs().size(); 

  if (nObs == 0) {
    return failure;
  }

  int MAXPRN = MAXPRN_GPS;
//  if (_useGlonass) {
//    MAXPRN = MAXPRN_GPS + MAXPRN_GLONASS;
//  }

  const int nCon = (_method == filter) ? 1 + MAXPRN : 0;

  AA.ReSize(nObs+nCon, nPar);  AA = 0.0;
  ll.ReSize(nObs+nCon);        ll = 0.0;
  PP.ReSize(nObs+nCon);        PP = 1.0 / (sigObs * sigObs);

  int iObs = 0;

  QVectorIterator<cmbCorr*> itCorr(corrs());
  while (itCorr.hasNext()) {
    cmbCorr* corr = itCorr.next();
    QString  prn  = corr->prn;

    ++iObs;

    if (corr->acName == _masterOrbitAC && resCorr.find(prn) == resCorr.end()) {
      resCorr[prn] = new t_corr(*corr);
    }

    for (int iPar = 1; iPar <= _params.size(); iPar++) {
      cmbParam* pp = _params[iPar-1];
      AA(iObs, iPar) = pp->partial(corr->acName, prn);
    }

    ll(iObs) = corr->dClk * t_CST::c - DotProduct(AA.Row(iObs), x0);
  }

  // Regularization
  // --------------
  if (_method == filter) {
    const double Ph = 1.e6;
    PP(nObs+1) = Ph;
    for (int iPar = 1; iPar <= _params.size(); iPar++) {
      cmbParam* pp = _params[iPar-1];
      if ( AA.Column(iPar).maximum_absolute_value() > 0.0 &&
           pp->type == cmbParam::clkSat ) {
        AA(nObs+1, iPar) = 1.0;
      }
    }
    int iCond = 1;
    for (int iGps = 1; iGps <= MAXPRN_GPS; iGps++) {
      QString prn = QString("G%1").arg(iGps, 2, 10, QChar('0'));
      ++iCond;
      PP(nObs+iCond) = Ph;
      for (int iPar = 1; iPar <= _params.size(); iPar++) {
        cmbParam* pp = _params[iPar-1];
        if ( AA.Column(iPar).maximum_absolute_value() > 0.0 &&
             pp->type == cmbParam::offACSat                 && 
             pp->prn == prn) {
          AA(nObs+iCond, iPar) = 1.0;
        }
      }
    }
//    if (_useGlonass) {
//      for (int iGlo = 1; iGlo <= MAXPRN_GLONASS; iGlo++) {
//        QString prn = QString("R%1").arg(iGlo, 2, 10, QChar('0'));
//        ++iCond;
//        PP(nObs+iCond) = Ph;
//        for (int iPar = 1; iPar <= _params.size(); iPar++) {
//          cmbParam* pp = _params[iPar-1];
//          if ( AA.Column(iPar).maximum_absolute_value() > 0.0 &&
//               pp->type == cmbParam::offACSat                 && 
//               pp->prn == prn) {
//            AA(nObs+iCond, iPar) = 1.0;
//          }
//        }
//      }
//    }
  }

  return success;
}

// Process Epoch - Single-Epoch Method
////////////////////////////////////////////////////////////////////////////
t_irc bncComb::processEpoch_singleEpoch(QTextStream& out,
                                        QMap<QString, t_corr*>& resCorr,
                                        ColumnVector& dx) {

  // Check Satellite Positions for Outliers
  // --------------------------------------
  if (checkOrbits(out) != success) {
    return failure;
  }

  // Outlier Detection Loop
  // ----------------------
  while (true) {
    
    // Remove Satellites that are not in Master
    // ----------------------------------------
    QMutableVectorIterator<cmbCorr*> it(corrs());
    while (it.hasNext()) {
      cmbCorr* corr = it.next();
      QString  prn  = corr->prn;
      bool foundMaster = false;
      QVectorIterator<cmbCorr*> itHlp(corrs());
      while (itHlp.hasNext()) {
        cmbCorr* corrHlp = itHlp.next();
        QString  prnHlp  = corrHlp->prn;
        QString  ACHlp   = corrHlp->acName;
        if (ACHlp == _masterOrbitAC && prn == prnHlp) {
          foundMaster = true;
          break;
        }
      }
      if (!foundMaster) {
        delete corr;
        it.remove();
      }
    }
    
    // Count Number of Observations per Satellite and per AC
    // -----------------------------------------------------
    QMap<QString, int> numObsPrn;
    QMap<QString, int> numObsAC;
    QVectorIterator<cmbCorr*> itCorr(corrs());
    while (itCorr.hasNext()) {
      cmbCorr* corr = itCorr.next();
      QString  prn  = corr->prn;
      QString  AC   = corr->acName;
      if (numObsPrn.find(prn) == numObsPrn.end()) {
        numObsPrn[prn]  = 1;
      }
      else {
        numObsPrn[prn] += 1;
      }
      if (numObsAC.find(AC) == numObsAC.end()) {
        numObsAC[AC]  = 1;
      }
      else {
        numObsAC[AC] += 1;
      }
    }
    
    // Clean-Up the Paramters
    // ----------------------
    for (int iPar = 1; iPar <= _params.size(); iPar++) {
      delete _params[iPar-1];
    }
    _params.clear();
    
    // Set new Parameters
    // ------------------
    int nextPar = 0;
    
    QMapIterator<QString, int> itAC(numObsAC);
    while (itAC.hasNext()) {
      itAC.next();
      const QString& AC     = itAC.key();
      int            numObs = itAC.value();
      if (AC != _masterOrbitAC && numObs > 0) {
        _params.push_back(new cmbParam(cmbParam::offACgps, ++nextPar, AC, ""));
        if (_useGlonass) {
          _params.push_back(new cmbParam(cmbParam::offACglo, ++nextPar, AC, ""));
        }
      }
    } 
    
    QMapIterator<QString, int> itPrn(numObsPrn);
    while (itPrn.hasNext()) {
      itPrn.next();
      const QString& prn    = itPrn.key();
      int            numObs = itPrn.value();
      if (numObs > 0) {
        _params.push_back(new cmbParam(cmbParam::clkSat, ++nextPar, "", prn));
      }
    }  
    
    int nPar = _params.size();
    ColumnVector x0(nPar); 
    x0 = 0.0;
    
    // Create First-Design Matrix
    // --------------------------
    Matrix         AA;
    ColumnVector   ll;
    DiagonalMatrix PP;
    if (createAmat(AA, ll, PP, x0, resCorr) != success) {
      return failure;
    }
    
    ColumnVector vv;
    try {
      Matrix          ATP = AA.t() * PP;
      SymmetricMatrix NN; NN << ATP * AA;
      ColumnVector    bb = ATP * ll;
      _QQ = NN.i();
      dx  = _QQ * bb;
      vv  = ll - AA * dx;
    }
    catch (Exception& exc) {
      out << exc.what() << endl;
      return failure;
    }

    int     maxResIndex;
    double  maxRes = vv.maximum_absolute_value1(maxResIndex);   
    out.setRealNumberNotation(QTextStream::FixedNotation);
    out.setRealNumberPrecision(3);  
    out << _resTime.datestr().c_str() << " " << _resTime.timestr().c_str()
        << " Maximum Residuum " << maxRes << ' '
        << corrs()[maxResIndex-1]->acName << ' ' << corrs()[maxResIndex-1]->prn;

    if (maxRes > _MAXRES) {
      out << "  Outlier" << endl;
      delete corrs()[maxResIndex-1];
      corrs().remove(maxResIndex-1);
    }
    else {
      out << "  OK" << endl;
      out.setRealNumberNotation(QTextStream::FixedNotation);
      out.setRealNumberPrecision(3);  
      for (int ii = 0; ii < vv.Nrows(); ii++) {
        const cmbCorr* corr = corrs()[ii];
        out << _resTime.datestr().c_str() << ' ' 
            << _resTime.timestr().c_str() << " "
            << corr->acName << ' ' << corr->prn;
        out.setFieldWidth(6);
        out << " dClk = " << corr->dClk * t_CST::c << " res = " << vv[ii] << endl;
        out.setFieldWidth(0);
      }
      return success;
    }

  }

  return failure;
}

// Check Satellite Positions for Outliers
////////////////////////////////////////////////////////////////////////////
t_irc bncComb::checkOrbits(QTextStream& out) {

  const double MAX_DISPLACEMENT = 0.20;

  // Switch to last ephemeris (if possible)
  // --------------------------------------
  QMutableVectorIterator<cmbCorr*> im(corrs());
  while (im.hasNext()) {
    cmbCorr* corr = im.next();
    QString  prn  = corr->prn;
    if      (_eph.find(prn) == _eph.end()) {
      out << "checkOrbit: missing eph (not found) " << corr->prn << endl;
      delete corr;
      im.remove();
    }
    else if (corr->eph == 0) {
      out << "checkOrbit: missing eph (zero) " << corr->prn << endl;
      delete corr;
      im.remove();
    }
    else {
      if ( corr->eph == _eph[prn]->last || corr->eph == _eph[prn]->prev ) {
        switchToLastEph(_eph[prn]->last, corr);
      }
      else {
        out << "checkOrbit: missing eph (deleted) " << corr->prn << endl;
        delete corr;
        im.remove();
      }
    }
  }

  while (true) {

    // Compute Mean Corrections for all Satellites
    // -------------------------------------------
    QMap<QString, int>          numCorr;
    QMap<QString, ColumnVector> meanRao;
    QVectorIterator<cmbCorr*> it(corrs());
    while (it.hasNext()) {
      cmbCorr* corr = it.next();
      QString  prn  = corr->prn;
      if (meanRao.find(prn) == meanRao.end()) {
        meanRao[prn].ReSize(4);
        meanRao[prn].Rows(1,3) = corr->rao;
        meanRao[prn](4)        = 1; 
      }
      else {
        meanRao[prn].Rows(1,3) += corr->rao;
        meanRao[prn](4)        += 1; 
      }
      if (numCorr.find(prn) == numCorr.end()) {
        numCorr[prn] = 1;
      }
      else {
        numCorr[prn] += 1;
      }
    }
    
    // Compute Differences wrt Mean, find Maximum
    // ------------------------------------------
    QMap<QString, cmbCorr*> maxDiff;
    it.toFront();
    while (it.hasNext()) {
      cmbCorr* corr = it.next();
      QString  prn  = corr->prn;
      if (meanRao[prn](4) != 0) {
        meanRao[prn] /= meanRao[prn](4);
        meanRao[prn](4) = 0;
      }
      corr->diffRao = corr->rao - meanRao[prn].Rows(1,3);
      if (maxDiff.find(prn) == maxDiff.end()) {
        maxDiff[prn] = corr;
      }
      else {
        double normMax = maxDiff[prn]->diffRao.norm_Frobenius();
        double norm    = corr->diffRao.norm_Frobenius();
        if (norm > normMax) {
          maxDiff[prn] = corr;
        }
      } 
    }
    
    if (_ACs.size() == 1) {
      break;
    }

    // Remove Outliers
    // ---------------
    bool removed = false;
    QMutableVectorIterator<cmbCorr*> im(corrs());
    while (im.hasNext()) {
      cmbCorr* corr = im.next();
      QString  prn  = corr->prn;
      if      (numCorr[prn] < 2) {
        delete corr;
        im.remove();
      }
      else if (corr == maxDiff[prn]) {
        double norm = corr->diffRao.norm_Frobenius();
        if (norm > MAX_DISPLACEMENT) {
          out << _resTime.datestr().c_str()    << " "
              << _resTime.timestr().c_str()    << " "
              << "Orbit Outlier: " 
              << corr->acName.toAscii().data() << " " 
              << prn.toAscii().data()          << " "
              << corr->iod                     << " " 
              << norm                          << endl;
          delete corr;
          im.remove();
          removed = true;
        }
      }
    }
    
    if (!removed) {
      break;
    }
  }

  return success;
}

// 
////////////////////////////////////////////////////////////////////////////
t_irc bncComb::mergeOrbitCorr(const cmbCorr* orbitCorr, cmbCorr* clkCorr) {

  clkCorr->iod       = orbitCorr->iod; // is it always correct?
  clkCorr->eph       = orbitCorr->eph; 
  clkCorr->tRao      = orbitCorr->tRao;
  clkCorr->rao       = orbitCorr->rao;
  clkCorr->dotRao    = orbitCorr->dotRao;
  clkCorr->dotDotRao = orbitCorr->dotDotRao;

  return success;
}