[u/mrichter/AliRoot.git] / TRD / AliTRDseedV1.cxx

/**************************************************************************
 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
 *                                                                        *
 * Author: The ALICE Off-line Project.                                    *
 * Contributors are mentioned in the code where appropriate.              *
 *                                                                        *
 * Permission to use, copy, modify and distribute this software and its   *
 * documentation strictly for non-commercial purposes is hereby granted   *
 * without fee, provided that the above copyright notice appears in all   *
 * copies and that both the copyright notice and this permission notice   *
 * appear in the supporting documentation. The authors make no claims     *
 * about the suitability of this software for any purpose. It is          *
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/

/* $Id$ */

////////////////////////////////////////////////////////////////////////////
//                                                                        //
//  The TRD track seed                                                    //
//                                                                        //
//  Authors:                                                              //
//    Alex Bercuci <A.Bercuci@gsi.de>                                     //
//    Markus Fasel <M.Fasel@gsi.de>                                       //
//                                                                        //
////////////////////////////////////////////////////////////////////////////

#include "TMath.h"
#include "TLinearFitter.h"
#include "TClonesArray.h" // tmp
#include <TTreeStream.h>

#include "AliLog.h"
#include "AliMathBase.h"

#include "AliTRDcluster.h"
#include "AliTRDseedV1.h"
#include "AliTRDtrackV1.h"
#include "AliTRDcalibDB.h"
#include "AliTRDchamberTimeBin.h"
#include "AliTRDtrackingChamber.h"
#include "AliTRDtrackerV1.h"
#include "AliTRDReconstructor.h"
#include "AliTRDrecoParam.h"
#include "AliTRDgeometry.h"
#include "Cal/AliTRDCalPID.h"

ClassImp(AliTRDseedV1)

//____________________________________________________________________
AliTRDseedV1::AliTRDseedV1(Int_t plane) 
  :AliTRDseed()
  ,fPlane(plane)
  ,fMom(0.)
  ,fSnp(0.)
  ,fTgl(0.)
  ,fdX(0.)
{
  //
  // Constructor
  //
	for(int islice=0; islice < knSlices; islice++) fdEdx[islice] = 0.;
	for(int ispec=0; ispec<AliPID::kSPECIES; ispec++) fProb[ispec]  = -1.;
}

//____________________________________________________________________
AliTRDseedV1::AliTRDseedV1(const AliTRDseedV1 &ref)
  :AliTRDseed((AliTRDseed&)ref)
  ,fPlane(ref.fPlane)
  ,fMom(ref.fMom)
  ,fSnp(ref.fSnp)
  ,fTgl(ref.fTgl)
  ,fdX(ref.fdX)
{
  //
  // Copy Constructor performing a deep copy
  //

	//AliInfo("");
	for(int islice=0; islice < knSlices; islice++) fdEdx[islice] = ref.fdEdx[islice];
	for(int ispec=0; ispec<AliPID::kSPECIES; ispec++) fProb[ispec] = ref.fProb[ispec];
}


//____________________________________________________________________
AliTRDseedV1& AliTRDseedV1::operator=(const AliTRDseedV1 &ref)
{
  //
  // Assignment Operator using the copy function
  //

	//AliInfo("");
	if(this != &ref){
		ref.Copy(*this);
	}
	return *this;

}

//____________________________________________________________________
AliTRDseedV1::~AliTRDseedV1()
{
  //
  // Destructor. The RecoParam object belongs to the underlying tracker.
  //

	//AliInfo(Form("fOwner[%s]", fOwner?"YES":"NO"));

	if(IsOwner()) 
		for(int itb=0; itb<knTimebins; itb++){
			if(!fClusters[itb]) continue; 
			//AliInfo(Form("deleting c %p @ %d", fClusters[itb], itb));
			delete fClusters[itb];
			fClusters[itb] = 0x0;
		}
}

//____________________________________________________________________
void AliTRDseedV1::Copy(TObject &ref) const
{
  //
  // Copy function
  //

	//AliInfo("");
	AliTRDseedV1 &target = (AliTRDseedV1 &)ref; 
	
	target.fPlane         = fPlane;
	target.fMom           = fMom;
	target.fSnp           = fSnp;
	target.fTgl           = fTgl;
	target.fdX            = fdX;
	
	for(int islice=0; islice < knSlices; islice++) target.fdEdx[islice] = fdEdx[islice];
	for(int ispec=0; ispec<AliPID::kSPECIES; ispec++) target.fProb[ispec] = fProb[ispec];
	
	AliTRDseed::Copy(target);
}


//____________________________________________________________
Bool_t AliTRDseedV1::Init(AliTRDtrackV1 *track)
{
// Initialize this tracklet using the track information
//
// Parameters:
//   track - the TRD track used to initialize the tracklet
// 
// Detailed description
// The function sets the starting point and direction of the
// tracklet according to the information from the TRD track.
// 
// Caution
// The TRD track has to be propagated to the beginning of the
// chamber where the tracklet will be constructed
//

	Double_t y, z; 
	if(!track->GetProlongation(fX0, y, z)) return kFALSE;
	fYref[0] = y;
	fYref[1] = track->GetSnp()/(1. - track->GetSnp()*track->GetSnp());
	fZref[0] = z;
	fZref[1] = track->GetTgl();

	//printf("Tracklet ref x[%7.3f] y[%7.3f] z[%7.3f], snp[%f] tgl[%f]\n", fX0, fYref[0], fZref[0], track->GetSnp(), track->GetTgl());
	return kTRUE;
}


//____________________________________________________________________
void AliTRDseedV1::CookdEdx(Int_t nslices)
{
// Calculates average dE/dx for all slices and store them in the internal array fdEdx. 
//
// Parameters:
//  nslices : number of slices for which dE/dx should be calculated
// Output:
//  store results in the internal array fdEdx. This can be accessed with the method
//  AliTRDseedV1::GetdEdx()
//
// Detailed description
// Calculates average dE/dx for all slices. Depending on the PID methode 
// the number of slices can be 3 (LQ) or 8(NN). 
// The calculation of dQ/dl are done using the tracklet fit results (see AliTRDseedV1::GetdQdl(Int_t)) i.e.
//
// dQ/dl = qc/(dx * sqrt(1 + dy/dx^2 + dz/dx^2))
//
// The following effects are included in the calculation:
// 1. calibration values for t0 and vdrift (using x coordinate to calculate slice)
// 2. cluster sharing (optional see AliTRDrecoParam::SetClusterSharing())
// 3. cluster size
//

	Int_t nclusters[knSlices];
	for(int i=0; i<knSlices; i++){ 
		fdEdx[i]     = 0.;
		nclusters[i] = 0;
	}
	Float_t clength = (/*.5 * */AliTRDgeometry::AmThick() + AliTRDgeometry::DrThick());

	AliTRDcluster *cluster = 0x0;
	for(int ic=0; ic<AliTRDtrackerV1::GetNTimeBins(); ic++){
		if(!(cluster = fClusters[ic])) continue;
		Float_t x = cluster->GetX();
		
		// Filter clusters for dE/dx calculation
		
		// 1.consider calibration effects for slice determination
		Int_t slice; 
		if(cluster->IsInChamber()) slice = Int_t(TMath::Abs(fX0 - x) * nslices / clength);
		else slice = x < fX0 ? 0 : nslices-1;
		
		// 2. take sharing into account
		Float_t w = cluster->IsShared() ? .5 : 1.;
		
		// 3. take into account large clusters TODO
		//w *= c->GetNPads() > 3 ? .8 : 1.;
		
		//CHECK !!!
		fdEdx[slice]   += w * GetdQdl(ic); //fdQdl[ic];
		nclusters[slice]++;
	} // End of loop over clusters

	if(AliTRDReconstructor::GetRecoParam()->GetPIDMethod() == AliTRDrecoParam::kLQPID){
	// calculate mean charge per slice (only LQ PID)
		for(int is=0; is<nslices; is++){ 
	    if(nclusters[is]) fdEdx[is] /= nclusters[is];
	  }
	}
}


//____________________________________________________________________
Float_t AliTRDseedV1::GetdQdl(Int_t ic) const
{
	return fClusters[ic] ? TMath::Abs(fClusters[ic]->GetQ()) /fdX / TMath::Sqrt(1. + fYfit[1]*fYfit[1] + fZref[1]*fZref[1]) : 0.;
}

//____________________________________________________________________
Double_t* AliTRDseedV1::GetProbability()
{	
// Fill probability array for tracklet from the DB.
//
// Parameters
//
// Output
//   returns pointer to the probability array and 0x0 if missing DB access 
//
// Detailed description

	
	// retrive calibration db
  AliTRDcalibDB *calibration = AliTRDcalibDB::Instance();
  if (!calibration) {
    AliError("No access to calibration data");
    return 0x0;
  }

  const AliTRDrecoParam *rec = AliTRDReconstructor::GetRecoParam();
  if (!rec) {
    AliError("No TRD reco param.");
    return 0x0;
  }

  // Retrieve the CDB container class with the parametric detector response
  const AliTRDCalPID *pd = calibration->GetPIDObject(rec->GetPIDMethod());
  if (!pd) {
    AliError("No access to AliTRDCalPID object");
    return 0x0;
  }
	//AliInfo(Form("Method[%d] : %s", AliTRDReconstructor::GetRecoParam()->GetPIDMethod(), pd->IsA()->GetName()));

	// calculate tracklet length TO DO
  Float_t length = (AliTRDgeometry::AmThick() + AliTRDgeometry::DrThick());
  /// TMath::Sqrt((1.0 - fSnp[iPlane]*fSnp[iPlane]) / (1.0 + fTgl[iPlane]*fTgl[iPlane]));
  
  //calculate dE/dx
  CookdEdx(rec->GetNdEdxSlices());
  
  // Sets the a priori probabilities
  for(int ispec=0; ispec<AliPID::kSPECIES; ispec++) {
    fProb[ispec] = pd->GetProbability(ispec, fMom, &fdEdx[0], length, fPlane);	
  }

	return &fProb[0];
}

//____________________________________________________________________
Float_t AliTRDseedV1::GetQuality(Bool_t kZcorr) const
{
  //
  // Returns a quality measurement of the current seed
  //

	Float_t zcorr = kZcorr ? fTilt * (fZProb - fZref[0]) : 0.;
	return 
		  .5 * TMath::Abs(18.0 - fN2)
		+ 10.* TMath::Abs(fYfit[1] - fYref[1])
		+ 5. * TMath::Abs(fYfit[0] - fYref[0] + zcorr)
		+ 2. * TMath::Abs(fMeanz - fZref[0]) / fPadLength;
}

//____________________________________________________________________
void AliTRDseedV1::GetCovAt(Double_t /*x*/, Double_t *cov) const
{
// Computes covariance in the y-z plane at radial point x

	Int_t ic = 0; while (!fClusters[ic]) ic++; 
  AliTRDcalibDB *fCalib = AliTRDcalibDB::Instance();
	Double_t exB         = fCalib->GetOmegaTau(fCalib->GetVdriftAverage(fClusters[ic]->GetDetector()), -AliTracker::GetBz()*0.1);

	Double_t sy2    = fSigmaY2*fSigmaY2 + .2*(fYfit[1]-exB)*(fYfit[1]-exB);
	Double_t sz2    = fPadLength/12.;


	//printf("Yfit[1] %f sy20 %f SigmaY2 %f\n", fYfit[1], sy20, fSigmaY2);

	cov[0] = sy2;
	cov[1] = fTilt*(sy2-sz2);
	cov[2] = sz2;
}


//____________________________________________________________________
void AliTRDseedV1::SetOwner(Bool_t own)
{
	//AliInfo(Form("own [%s] fOwner[%s]", own?"YES":"NO", fOwner?"YES":"NO"));
	
	if(own){
		for(int ic=0; ic<knTimebins; ic++){
			if(!fClusters[ic]) continue;
			fClusters[ic] = new AliTRDcluster(*fClusters[ic]);
		}
		SetBit(1);
	} else {
		if(IsOwner()){
			for(int ic=0; ic<knTimebins; ic++){
				if(!fClusters[ic]) continue;
				delete fClusters[ic];
				//fClusters[ic] = tracker->GetClusters(index) TODO
			}
		}
		SetBit(1, kFALSE);
	}
}

//____________________________________________________________________
Bool_t	AliTRDseedV1::AttachClustersIter(AliTRDtrackingChamber *chamber, Float_t quality, Bool_t kZcorr, AliTRDcluster *c)
{
  //
  // Iterative process to register clusters to the seed.
  // In iteration 0 we try only one pad-row and if quality not
  // sufficient we try 2 pad-rows (about 5% of tracks cross 2 pad-rows)
  //
	// debug level 7
	//
	
	if(!AliTRDReconstructor::GetRecoParam()){
		AliError("Seed can not be used without a valid RecoParam.");
		return kFALSE;
	}

	AliTRDchamberTimeBin *layer = 0x0;
	if(AliTRDReconstructor::GetRecoParam()->GetStreamLevel()>=7 && c){
		TClonesArray clusters("AliTRDcluster", 24);
		clusters.SetOwner(kTRUE);
		AliTRDcluster *cc = 0x0;
		Int_t det=-1, ncl, ncls = 0;
		for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
			if(!(layer = chamber->GetTB(iTime))) continue;
			if(!(ncl = Int_t(*layer))) continue;
			for(int ic=0; ic<ncl; ic++){ 
				cc = (*layer)[ic];
				det = cc->GetDetector();
				new(clusters[ncls++]) AliTRDcluster(*cc);
			}
		}
		AliInfo(Form("N clusters[%d] = %d", fPlane, ncls));
		
		Int_t ref = c ? 1 : 0;
		TTreeSRedirector &cstreamer = *AliTRDtrackerV1::DebugStreamer();
		cstreamer << "AttachClustersIter"
			<< "det="        << det 
			<< "ref="        << ref 
			<< "clusters.="  << &clusters
			<< "tracklet.="  << this
			<< "cl.="        << c
			<< "\n";	
	}

	Float_t  tquality;
	Double_t kroady = AliTRDReconstructor::GetRecoParam()->GetRoad1y();
	Double_t kroadz = fPadLength * .5 + 1.;
	
	// initialize configuration parameters
	Float_t zcorr = kZcorr ? fTilt * (fZProb - fZref[0]) : 0.;
	Int_t   niter = kZcorr ? 1 : 2;
	
	Double_t yexp, zexp;
	Int_t ncl = 0;
	// start seed update
	for (Int_t iter = 0; iter < niter; iter++) {
		ncl = 0;
		for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
			if(!(layer = chamber->GetTB(iTime))) continue;
			if(!Int_t(*layer)) continue;
			
			// define searching configuration
			Double_t dxlayer = layer->GetX() - fX0;
			if(c){
				zexp = c->GetZ();
				//Try 2 pad-rows in second iteration
				if (iter > 0) {
					zexp = fZref[0] + fZref[1] * dxlayer - zcorr;
					if (zexp > c->GetZ()) zexp = c->GetZ() + fPadLength*0.5;
					if (zexp < c->GetZ()) zexp = c->GetZ() - fPadLength*0.5;
				}
			} else zexp = fZref[0] + (kZcorr ? fZref[1] * dxlayer : 0.);
			yexp  = fYref[0] + fYref[1] * dxlayer - zcorr;
			
			// Get and register cluster
			Int_t    index = layer->SearchNearestCluster(yexp, zexp, kroady, kroadz);
			if (index < 0) continue;
			AliTRDcluster *cl = (*layer)[index];
			
			fIndexes[iTime]  = layer->GetGlobalIndex(index);
			fClusters[iTime] = cl;
			fY[iTime]        = cl->GetY();
			fZ[iTime]        = cl->GetZ();
			ncl++;
		}
  	if(AliTRDReconstructor::GetRecoParam()->GetStreamLevel()>=7) AliInfo(Form("iter = %d ncl [%d] = %d", iter, fPlane, ncl));
		
		if(ncl>1){	
			// calculate length of the time bin (calibration aware)
			Int_t irp = 0; Float_t x[2]; Int_t tb[2];
			for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
				if(!fClusters[iTime]) continue;
				x[irp]  = fClusters[iTime]->GetX();
				tb[irp] = iTime;
				irp++;
				if(irp==2) break;
			} 
			fdX = (x[1] - x[0]) / (tb[0] - tb[1]);
	
			// update X0 from the clusters (calibration/alignment aware)
			for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
				if(!(layer = chamber->GetTB(iTime))) continue;
				if(!layer->IsT0()) continue;
				if(fClusters[iTime]){ 
					fX0 = fClusters[iTime]->GetX();
					break;
				} else { // we have to infere the position of the anode wire from the other clusters
					for (Int_t jTime = iTime+1; jTime < AliTRDtrackerV1::GetNTimeBins(); jTime++) {
						if(!fClusters[jTime]) continue;
						fX0 = fClusters[jTime]->GetX() + fdX * (jTime - iTime);
					}
					break;
				}
			}	
			
			// update YZ reference point
			// TODO
			
			// update x reference positions (calibration/alignment aware)
			for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
				if(!fClusters[iTime]) continue;
				fX[iTime] = fClusters[iTime]->GetX() - fX0;
			} 
			
			AliTRDseed::Update();
		}
  	if(AliTRDReconstructor::GetRecoParam()->GetStreamLevel()>=7) AliInfo(Form("iter = %d nclFit [%d] = %d", iter, fPlane, fN2));
		
		if(IsOK()){
			tquality = GetQuality(kZcorr);
			if(tquality < quality) break;
			else quality = tquality;
		}
		kroadz *= 2.;
	} // Loop: iter
	if (!IsOK()) return kFALSE;

	CookLabels();
	UpdateUsed();
	return kTRUE;	
}

//____________________________________________________________________
Bool_t	AliTRDseedV1::AttachClusters(AliTRDtrackingChamber *chamber
                                       ,Bool_t kZcorr)
{
  //
  // Projective algorithm to attach clusters to seeding tracklets
  //
  // Parameters
  //
  // Output
  //
  // Detailed description
  // 1. Collapse x coordinate for the full detector plane
  // 2. truncated mean on y (r-phi) direction
  // 3. purge clusters
  // 4. truncated mean on z direction
  // 5. purge clusters
  // 6. fit tracklet
  //	

	if(!AliTRDReconstructor::GetRecoParam()){
		AliError("Seed can not be used without a valid RecoParam.");
		return kFALSE;
	}

	const Int_t kClusterCandidates = 2 * knTimebins;
	
	//define roads
	Double_t kroady = AliTRDReconstructor::GetRecoParam()->GetRoad1y();
	Double_t kroadz = fPadLength * 1.5 + 1.;
	// correction to y for the tilting angle
	Float_t zcorr = kZcorr ? fTilt * (fZProb - fZref[0]) : 0.;

	// working variables
	AliTRDcluster *clusters[kClusterCandidates];
	Double_t cond[4], yexp[knTimebins], zexp[knTimebins],
		yres[kClusterCandidates], zres[kClusterCandidates];
	Int_t ncl, *index = 0x0, tboundary[knTimebins];
	
	// Do cluster projection
	AliTRDchamberTimeBin *layer = 0x0;
	Int_t nYclusters = 0; Bool_t kEXIT = kFALSE;
	for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
		if(!(layer = chamber->GetTB(iTime))) continue;
		if(!Int_t(*layer)) continue;
		
		fX[iTime] = layer->GetX() - fX0;
		zexp[iTime] = fZref[0] + fZref[1] * fX[iTime];
		yexp[iTime] = fYref[0] + fYref[1] * fX[iTime] - zcorr;
		
		// build condition and process clusters
		cond[0] = yexp[iTime] - kroady; cond[1] = yexp[iTime] + kroady;
		cond[2] = zexp[iTime] - kroadz; cond[3] = zexp[iTime] + kroadz;
		layer->GetClusters(cond, index, ncl);
		for(Int_t ic = 0; ic<ncl; ic++){
			AliTRDcluster *c = layer->GetCluster(index[ic]);
			clusters[nYclusters] = c;
			yres[nYclusters++] = c->GetY() - yexp[iTime];
			if(nYclusters >= kClusterCandidates) {
				AliWarning(Form("Cluster candidates reached limit %d. Some may be lost.", kClusterCandidates));
				kEXIT = kTRUE;
				break;
			}
		}
		tboundary[iTime] = nYclusters;
		if(kEXIT) break;
	}
	
	// Evaluate truncated mean on the y direction
	Double_t mean, sigma;
	AliMathBase::EvaluateUni(nYclusters, yres, mean, sigma, Int_t(nYclusters*.8)-2);
	// purge cluster candidates
	Int_t nZclusters = 0;
	for(Int_t ic = 0; ic<nYclusters; ic++){
		if(yres[ic] - mean > 4. * sigma){
			clusters[ic] = 0x0;
			continue;
		}
		zres[nZclusters++] = clusters[ic]->GetZ() - zexp[clusters[ic]->GetLocalTimeBin()];
	}
	
	// Evaluate truncated mean on the z direction
	AliMathBase::EvaluateUni(nZclusters, zres, mean, sigma, Int_t(nZclusters*.8)-2);
	// purge cluster candidates
	for(Int_t ic = 0; ic<nZclusters; ic++){
		if(zres[ic] - mean > 4. * sigma){
			clusters[ic] = 0x0;
			continue;
		}
	}

	
	// Select only one cluster/TimeBin
	Int_t lastCluster = 0;
	fN2 = 0;
	for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
		ncl = tboundary[iTime] - lastCluster;
		if(!ncl) continue;
		Int_t iptr = lastCluster;
		if(ncl > 1){
			Float_t dold = 9999.;
			for(int ic=lastCluster; ic<tboundary[iTime]; ic++){
				if(!clusters[ic]) continue;
				Float_t y = yexp[iTime] - clusters[ic]->GetY();
				Float_t z = zexp[iTime] - clusters[ic]->GetZ();
				Float_t d = y * y + z * z;
				if(d > dold) continue;
				dold = d;
				iptr = ic;
			}
		}
		fIndexes[iTime]  = chamber->GetTB(iTime)->GetGlobalIndex(iptr);
		fClusters[iTime] = clusters[iptr];
		fY[iTime]        = clusters[iptr]->GetY();
		fZ[iTime]        = clusters[iptr]->GetZ();
		lastCluster      = tboundary[iTime];
		fN2++;
	}
	
	// number of minimum numbers of clusters expected for the tracklet
	Int_t kClmin = Int_t(AliTRDReconstructor::GetRecoParam()->GetFindableClusters()*AliTRDtrackerV1::GetNTimeBins());
  if (fN2 < kClmin){
		AliWarning(Form("Not enough clusters to fit the tracklet %d [%d].", fN2, kClmin));
    fN2 = 0;
    return kFALSE;
  }

	// update used clusters
	fNUsed = 0;
	for (Int_t iTime = 0; iTime < AliTRDtrackerV1::GetNTimeBins(); iTime++) {
		if(!fClusters[iTime]) continue;
		if((fClusters[iTime]->IsUsed())) fNUsed++;
	}

  if (fN2-fNUsed < kClmin){
		AliWarning(Form("Too many clusters already in use %d (from %d).", fNUsed, fN2));
    fN2 = 0;
    return kFALSE;
  }
	
	return kTRUE;
}

//____________________________________________________________________
Bool_t AliTRDseedV1::Fit()
{
  //
  // Linear fit of the tracklet
  //
  // Parameters :
  //
  // Output :
  //  True if successful
  //
  // Detailed description
  // 2. Check if tracklet crosses pad row boundary
  // 1. Calculate residuals in the y (r-phi) direction
  // 3. Do a Least Square Fit to the data
  //

	const Int_t kClmin = 8;
	const Int_t kNtb = AliTRDtrackerV1::GetNTimeBins();
	AliTRDtrackerV1::AliTRDLeastSquare fitterY, fitterZ;

	// convertion factor from square to gauss distribution for sigma
	Double_t convert = 1./TMath::Sqrt(12.);

	// book cluster information
	Double_t xc[knTimebins+1], yc[knTimebins], zc[knTimebins+1], sy[knTimebins], sz[knTimebins+1];
	Int_t zRow[knTimebins];
	AliTRDcluster *c = 0x0;
	Int_t nc = 0;
	for (Int_t ic=0; ic<kNtb; ic++) {
		zRow[ic] = -1;
		xc[ic]  = -1.;
		yc[ic]  = 999.;
		zc[ic]  = 999.;
		sy[ic]  = 0.;
		sz[ic]  = 0.;
		if(!(c = fClusters[ic])) continue;
		if(!c->IsInChamber()) continue;
		Float_t w = 1.;
		if(c->GetNPads()>4) w = .5;
		if(c->GetNPads()>5) w = .2;
		zRow[nc] = c->GetPadRow();
		xc[nc]   = fX0 - c->GetX();
		yc[nc]   = c->GetY();
		zc[nc]   = c->GetZ();
		sy[ic]   = w; // all clusters have the same sigma
		sz[ic]   = fPadLength*convert;
		fitterZ.AddPoint(&xc[ic], zc[ic], sz[ic]);
		nc++;
	}
  // to few clusters
	if (nc < kClmin) return kFALSE; 
	

	Int_t zN[2*35];
  Int_t nz = AliTRDtrackerV1::Freq(nc, zRow, zN, kFALSE);
	// more than one pad row crossing
	if(nz>2) return kFALSE; 
	
	// estimate reference parameter at average x
	Double_t y0 = fYref[0];
	Double_t dydx = fYref[1]; 
	Double_t dzdx = fZref[1];
	zc[nc]  = fZref[0];

	// determine z offset of the fit
	Int_t nchanges = 0, nCross = 0;
	if(nz==2){ // tracklet is crossing pad row
		// Find the break time allowing one chage on pad-rows
		// with maximal number of accepted clusters
		Int_t padRef = zRow[0];
		for (Int_t ic=1; ic<nc; ic++) {
			if(zRow[ic] == padRef) continue;
			
			// debug
			if(zRow[ic-1] == zRow[ic]){
				printf("ERROR in pad row change!!!\n");
			}
		
			// evaluate parameters of the crossing point
			Float_t sx = (xc[ic-1] - xc[ic])*convert;
			xc[nc] = .5 * (xc[ic-1] + xc[ic]);
			zc[nc] = .5 * (zc[ic-1] + zc[ic]);
			sz[nc] = TMath::Max(dzdx * sx, .01);
			dzdx   = zc[ic-1] > zc[ic] ? 1. : -1.;
			padRef = zRow[ic];
			nCross = ic;
			nchanges++;
		}
	}

	// condition on nCross and reset nchanges TODO

	if(nchanges==1){
		if(dzdx * fZref[1] < 0.){
			AliInfo("tracklet direction does not correspond to the track direction. TODO.");
		}
		SetBit(2, kTRUE); // mark pad row crossing
		fCross[0] = xc[nc]; fCross[2] = zc[nc]; fCross[3] = sz[nc]; 
		fitterZ.AddPoint(&xc[nc], zc[nc], sz[nc]);
		fitterZ.Eval();
		dzdx = fZref[1]; // we don't trust Parameter[1] ??;
		zc[nc] = fitterZ.GetFunctionParameter(0); 
	} else if(nchanges > 1){ // debug
		AliInfo("ERROR in n changes!!!");
		return kFALSE;
	}

	
	// estimate deviation from reference direction
	dzdx *= fTilt;
	for (Int_t ic=0; ic<nc; ic++) {
		yc[ic] -= y0 + xc[ic]*(dydx + dzdx) + fTilt * (zc[ic] - zc[nc]);
		fitterY.AddPoint(&xc[ic], yc[ic], sy[ic]);
	}
	fitterY.Eval();
	fYfit[0] = y0+fitterY.GetFunctionParameter(0);
	fYfit[1] = dydx+fitterY.GetFunctionParameter(1);
	if(nchanges) fCross[1] = fYfit[0] + fCross[0] * fYfit[1];

// 	printf("\nnz = %d\n", nz);
// 	for(int ic=0; ic<35; ic++) printf("%d row[%d]\n", ic, zRow[ic]);	
// 
// 	for(int ic=0; ic<nz; ic++) printf("%d n[%d]\n", ic, zN[ic]);	

	return kTRUE;
}

//___________________________________________________________________
void AliTRDseedV1::Draw(Option_t*)
{
}

//___________________________________________________________________
void AliTRDseedV1::Print(Option_t*) const
{
  //
  // Printing the seedstatus
  //

	printf("Seed status :\n");
	printf("  fTilt      = %f\n", fTilt);
	printf("  fPadLength = %f\n", fPadLength);
	printf("  fX0        = %f\n", fX0);
	for(int ic=0; ic<AliTRDtrackerV1::GetNTimeBins(); ic++) {
          const Char_t *isUsable = fUsable[ic]?"Yes":"No";
	  printf("  %d X[%f] Y[%f] Z[%f] Indexes[%d] clusters[%p] usable[%s]\n"
                , ic
                , fX[ic]
                , fY[ic]
                , fZ[ic]
                , fIndexes[ic]
                , ((void*) fClusters[ic])
                , isUsable);
        }

	printf("  fYref[0] =%f fYref[1] =%f\n", fYref[0], fYref[1]);
	printf("  fZref[0] =%f fZref[1] =%f\n", fZref[0], fZref[1]);
	printf("  fYfit[0] =%f fYfit[1] =%f\n", fYfit[0], fYfit[1]);
	printf("  fYfitR[0]=%f fYfitR[1]=%f\n", fYfitR[0], fYfitR[1]);
	printf("  fZfit[0] =%f fZfit[1] =%f\n", fZfit[0], fZfit[1]);
	printf("  fZfitR[0]=%f fZfitR[1]=%f\n", fZfitR[0], fZfitR[1]);
	printf("  fSigmaY =%f\n", fSigmaY);
	printf("  fSigmaY2=%f\n", fSigmaY2);            
	printf("  fMeanz  =%f\n", fMeanz);
	printf("  fZProb  =%f\n", fZProb);
	printf("  fLabels[0]=%d fLabels[1]=%d\n", fLabels[0], fLabels[1]);
	printf("  fN      =%d\n", fN);
	printf("  fN2     =%d (>8 isOK)\n",fN2);
	printf("  fNUsed  =%d\n", fNUsed);
	printf("  fFreq   =%d\n", fFreq);
	printf("  fNChange=%d\n",  fNChange);
	printf("  fMPads  =%f\n", fMPads);
	
	printf("  fC      =%f\n", fC);        
	printf("  fCC     =%f\n",fCC);      
	printf("  fChi2   =%f\n", fChi2);  
	printf("  fChi2Z  =%f\n", fChi2Z);
}