Moved old AliMagFCheb to AliMagF, small fixes/optimizations in field classes
[u/mrichter/AliRoot.git] / ITS / AliITStrackV2.cxx
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006b5f7f 1/**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
3 * *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
6 * *
7 * Permission to use, copy, modify and distribute this software and its *
8 * documentation strictly for non-commercial purposes is hereby granted *
9 * without fee, provided that the above copyright notice appears in all *
10 * copies and that both the copyright notice and this permission notice *
11 * appear in the supporting documentation. The authors make no claims *
12 * about the suitability of this software for any purpose. It is *
13 * provided "as is" without express or implied warranty. *
14 **************************************************************************/
15
ae00569a 16/* $Id$ */
17
66e811e2 18///////////////////////////////////////////////////////////////////////////
006b5f7f 19// Implementation of the ITS track class
20//
21// Origin: Iouri Belikov, CERN, Jouri.Belikov@cern.ch
a9a2d814 22// dEdx analysis by: Boris Batyunya, JINR, Boris.Batiounia@cern.ch
66e811e2 23///////////////////////////////////////////////////////////////////////////
006b5f7f 24#include <TMath.h>
006b5f7f 25
26#include "AliCluster.h"
6c94f330 27#include "AliTracker.h"
83d73500 28#include "AliESDtrack.h"
58e536c5 29#include "AliESDVertex.h"
8a84886c 30#include "AliITSReconstructor.h"
006b5f7f 31#include "AliITStrackV2.h"
32
8602c008 33const Int_t AliITStrackV2::fgkWARN = 5;
34
1aedd96e 35ClassImp(AliITStrackV2)
8676d691 36
e43c066c 37
006b5f7f 38//____________________________________________________________________________
6c94f330 39AliITStrackV2::AliITStrackV2() : AliKalmanTrack(),
22b13da0 40 fdEdx(0),
83d73500 41 fESDtrack(0)
e43c066c 42{
ae00569a 43 for(Int_t i=0; i<2*AliITSgeomTGeo::kNLayers; i++) {fIndex[i]=-1; fModule[i]=-1;}
44 for(Int_t i=0; i<4; i++) fdEdxSample[i]=0;
e43c066c 45}
46
83d73500 47
22b13da0 48//____________________________________________________________________________
67c3dcbe 49AliITStrackV2::AliITStrackV2(AliESDtrack& t,Bool_t c) throw (const Char_t *) :
6c94f330 50 AliKalmanTrack(),
51 fdEdx(t.GetITSsignal()),
52 fESDtrack(&t)
53{
83d73500 54 //------------------------------------------------------------------
67c3dcbe 55 // Conversion ESD track -> ITS track.
56 // If c==kTRUE, create the ITS track out of the constrained params.
83d73500 57 //------------------------------------------------------------------
6c94f330 58 const AliExternalTrackParam *par=&t;
59 if (c) {
6c4ef2ed 60 par=t.GetConstrainedParam();
6c94f330 61 if (!par) throw "AliITStrackV2: conversion failed !\n";
62 }
63 Set(par->GetX(),par->GetAlpha(),par->GetParameter(),par->GetCovariance());
64
65 //if (!Invariant()) throw "AliITStrackV2: conversion failed !\n";
66
83d73500 67 SetLabel(t.GetLabel());
68 SetMass(t.GetMass());
6c94f330 69 SetNumberOfClusters(t.GetITSclusters(fIndex));
006b5f7f 70
83d73500 71 if (t.GetStatus()&AliESDtrack::kTIME) {
72 StartTimeIntegral();
73 Double_t times[10]; t.GetIntegratedTimes(times); SetIntegratedTimes(times);
74 SetIntegratedLength(t.GetIntegratedLength());
75 }
e43c066c 76
68b8060b 77 for(Int_t i=0; i<4; i++) fdEdxSample[i]=0;
006b5f7f 78}
79
7ac23097 80//____________________________________________________________________________
81void AliITStrackV2::ResetClusters() {
82 //------------------------------------------------------------------
83 // Reset the array of attached clusters.
84 //------------------------------------------------------------------
85 for (Int_t i=0; i<2*AliITSgeomTGeo::kNLayers; i++) fIndex[i]=-1;
86 SetChi2(0.);
87 SetNumberOfClusters(0);
88}
89
15dd636f 90void AliITStrackV2::UpdateESDtrack(ULong_t flags) const {
83d73500 91 fESDtrack->UpdateTrackParams(this,flags);
ae00569a 92 // copy the module indices
93 for(Int_t i=0;i<12;i++) {
94 // printf(" %d\n",GetModuleIndex(i));
95 fESDtrack->SetITSModuleIndex(i,GetModuleIndex(i));
96 }
83d73500 97}
98
006b5f7f 99//____________________________________________________________________________
6c94f330 100AliITStrackV2::AliITStrackV2(const AliITStrackV2& t) :
101 AliKalmanTrack(t),
102 fdEdx(t.fdEdx),
103 fESDtrack(t.fESDtrack)
104{
006b5f7f 105 //------------------------------------------------------------------
106 //Copy constructor
107 //------------------------------------------------------------------
ef7253ac 108 Int_t i;
ef7253ac 109 for (i=0; i<4; i++) fdEdxSample[i]=t.fdEdxSample[i];
ae00569a 110 for (i=0; i<2*AliITSgeomTGeo::GetNLayers(); i++) {
111 fIndex[i]=t.fIndex[i];
112 fModule[i]=t.fModule[i];
113 }
006b5f7f 114}
a9a2d814 115
006b5f7f 116//_____________________________________________________________________________
117Int_t AliITStrackV2::Compare(const TObject *o) const {
118 //-----------------------------------------------------------------
119 // This function compares tracks according to the their curvature
120 //-----------------------------------------------------------------
7f6ddf58 121 AliITStrackV2 *t=(AliITStrackV2*)o;
6c23ffed 122 //Double_t co=OneOverPt();
123 //Double_t c =OneOverPt();
15dd636f 124 Double_t co=t->GetSigmaY2()*t->GetSigmaZ2();
125 Double_t c =GetSigmaY2()*GetSigmaZ2();
006b5f7f 126 if (c>co) return 1;
127 else if (c<co) return -1;
128 return 0;
129}
130
006b5f7f 131//____________________________________________________________________________
6c94f330 132Bool_t
133AliITStrackV2::PropagateToVertex(const AliESDVertex *v,Double_t d,Double_t x0)
134{
006b5f7f 135 //------------------------------------------------------------------
136 //This function propagates a track to the minimal distance from the origin
6c94f330 137 //------------------------------------------------------------------
138 Double_t bz=GetBz();
e50912db 139 if (PropagateToDCA(v,bz,kVeryBig)) {
140 Double_t xOverX0,xTimesRho;
141 xOverX0 = d; xTimesRho = d*x0;
142 if (CorrectForMeanMaterial(xOverX0,xTimesRho,kTRUE)) return kTRUE;
143 }
6c94f330 144 return kFALSE;
006b5f7f 145}
146
147//____________________________________________________________________________
6c94f330 148Bool_t AliITStrackV2::
e50912db 149GetGlobalXYZat(Double_t xloc, Double_t &x, Double_t &y, Double_t &z) const {
006b5f7f 150 //------------------------------------------------------------------
151 //This function returns a track position in the global system
152 //------------------------------------------------------------------
6c94f330 153 Double_t r[3];
e50912db 154 Bool_t rc=GetXYZAt(xloc, AliTracker::GetBz(), r);
6c94f330 155 x=r[0]; y=r[1]; z=r[2];
156 return rc;
006b5f7f 157}
158
159//_____________________________________________________________________________
6c94f330 160Double_t AliITStrackV2::GetPredictedChi2(const AliCluster *c) const {
006b5f7f 161 //-----------------------------------------------------------------
162 // This function calculates a predicted chi2 increment.
163 //-----------------------------------------------------------------
6c94f330 164 Double_t p[2]={c->GetY(), c->GetZ()};
165 Double_t cov[3]={c->GetSigmaY2(), 0., c->GetSigmaZ2()};
166 return AliExternalTrackParam::GetPredictedChi2(p,cov);
a9a2d814 167}
168
169//____________________________________________________________________________
6c94f330 170Bool_t AliITStrackV2::PropagateTo(Double_t xk, Double_t d, Double_t x0) {
006b5f7f 171 //------------------------------------------------------------------
172 //This function propagates a track
173 //------------------------------------------------------------------
afd25725 174
6c94f330 175 Double_t oldX=GetX(), oldY=GetY(), oldZ=GetZ();
006b5f7f 176
6c94f330 177 Double_t bz=GetBz();
178 if (!AliExternalTrackParam::PropagateTo(xk,bz)) return kFALSE;
e50912db 179 Double_t xOverX0,xTimesRho;
180 xOverX0 = d; xTimesRho = d*x0;
181 if (!CorrectForMeanMaterial(xOverX0,xTimesRho,kTRUE)) return kFALSE;
006b5f7f 182
dd44614b 183 Double_t x=GetX(), y=GetY(), z=GetZ();
6c94f330 184 if (IsStartedTimeIntegral() && x>oldX) {
185 Double_t l2 = (x-oldX)*(x-oldX) + (y-oldY)*(y-oldY) + (z-oldZ)*(z-oldZ);
f29dbb4b 186 AddTimeStep(TMath::Sqrt(l2));
187 }
f29dbb4b 188
6c94f330 189 return kTRUE;
006b5f7f 190}
191
192//____________________________________________________________________________
db355ee7 193Bool_t AliITStrackV2::PropagateToTGeo(Double_t xToGo, Int_t nstep, Double_t &xOverX0, Double_t &xTimesRho, Bool_t addTime) {
afd25725 194 //-------------------------------------------------------------------
195 // Propagates the track to a reference plane x=xToGo in n steps.
196 // These n steps are only used to take into account the curvature.
197 // The material is calculated with TGeo. (L.Gaudichet)
198 //-------------------------------------------------------------------
199
200 Double_t startx = GetX(), starty = GetY(), startz = GetZ();
201 Double_t sign = (startx<xToGo) ? -1.:1.;
202 Double_t step = (xToGo-startx)/TMath::Abs(nstep);
203
204 Double_t start[3], end[3], mparam[7], bz = GetBz();
205 Double_t x = startx;
206
207 for (Int_t i=0; i<nstep; i++) {
208
209 GetXYZ(start); //starting global position
210 x += step;
211 if (!GetXYZAt(x, bz, end)) return kFALSE;
212 if (!AliExternalTrackParam::PropagateTo(x, bz)) return kFALSE;
213 AliTracker::MeanMaterialBudget(start, end, mparam);
afd25725 214 if (mparam[1]<900000) {
e50912db 215 xTimesRho = sign*mparam[4]*mparam[0];
216 xOverX0 = mparam[1];
afd25725 217 if (!AliExternalTrackParam::CorrectForMeanMaterial(xOverX0,
e50912db 218 xTimesRho,GetMass())) return kFALSE;
afd25725 219 }
220 }
221
db355ee7 222 if (addTime && IsStartedTimeIntegral() && GetX()>startx) {
afd25725 223 Double_t l2 = ( (GetX()-startx)*(GetX()-startx) +
224 (GetY()-starty)*(GetY()-starty) +
225 (GetZ()-startz)*(GetZ()-startz) );
226 AddTimeStep(TMath::Sqrt(l2));
227 }
228
229 return kTRUE;
230}
231
232//____________________________________________________________________________
6c94f330 233Bool_t AliITStrackV2::Update(const AliCluster* c, Double_t chi2, Int_t index)
234{
006b5f7f 235 //------------------------------------------------------------------
236 //This function updates track parameters
237 //------------------------------------------------------------------
6c94f330 238 Double_t p[2]={c->GetY(), c->GetZ()};
239 Double_t cov[3]={c->GetSigmaY2(), 0., c->GetSigmaZ2()};
006b5f7f 240
6c94f330 241 if (!AliExternalTrackParam::Update(p,cov)) return kFALSE;
006b5f7f 242
28d5b13d 243 Int_t n=GetNumberOfClusters();
006b5f7f 244 if (!Invariant()) {
28d5b13d 245 if (n>fgkWARN) AliWarning("Wrong invariant !");
6c94f330 246 return kFALSE;
006b5f7f 247 }
248
6c94f330 249 if (chi2<0) return kTRUE;
67c3dcbe 250
150f264c 251 AliTracker::FillResiduals(this,p,cov,c->GetVolumeId());
252
006b5f7f 253 fIndex[n]=index;
254 SetNumberOfClusters(n+1);
255 SetChi2(GetChi2()+chi2);
256
6c94f330 257 return kTRUE;
006b5f7f 258}
259
6c94f330 260Bool_t AliITStrackV2::Invariant() const {
006b5f7f 261 //------------------------------------------------------------------
262 // This function is for debugging purpose only
263 //------------------------------------------------------------------
7f6ddf58 264 Int_t n=GetNumberOfClusters();
6c94f330 265
8a84886c 266 // take into account the misalignment error
267 Float_t maxMisalErrY2=0,maxMisalErrZ2=0;
268 for (Int_t lay=0; lay<AliITSgeomTGeo::kNLayers; lay++) {
269 maxMisalErrY2 = TMath::Max(maxMisalErrY2,AliITSReconstructor::GetRecoParam()->GetClusterMisalErrorY(lay));
270 maxMisalErrZ2 = TMath::Max(maxMisalErrZ2,AliITSReconstructor::GetRecoParam()->GetClusterMisalErrorZ(lay));
271 }
272 maxMisalErrY2 *= maxMisalErrY2;
273 maxMisalErrZ2 *= maxMisalErrZ2;
274 // this is because when we reset before refitting, we multiply the
275 // matrix by 10
276 maxMisalErrY2 *= 10.;
277 maxMisalErrZ2 *= 10.;
278
6c94f330 279 Double_t sP2=GetParameter()[2];
280 if (TMath::Abs(sP2) >= kAlmost1){
8602c008 281 if (n>fgkWARN) Warning("Invariant","fP2=%f\n",sP2);
6c94f330 282 return kFALSE;
a9a2d814 283 }
6c94f330 284 Double_t sC00=GetCovariance()[0];
8a84886c 285 if (sC00<=0 || sC00>(9.+maxMisalErrY2)) {
8602c008 286 if (n>fgkWARN) Warning("Invariant","fC00=%f\n",sC00);
6c94f330 287 return kFALSE;
a9a2d814 288 }
6c94f330 289 Double_t sC11=GetCovariance()[2];
8a84886c 290 if (sC11<=0 || sC11>(9.+maxMisalErrZ2)) {
8602c008 291 if (n>fgkWARN) Warning("Invariant","fC11=%f\n",sC11);
6c94f330 292 return kFALSE;
a9a2d814 293 }
6c94f330 294 Double_t sC22=GetCovariance()[5];
295 if (sC22<=0 || sC22>1.) {
8602c008 296 if (n>fgkWARN) Warning("Invariant","fC22=%f\n",sC22);
6c94f330 297 return kFALSE;
a9a2d814 298 }
6c94f330 299 Double_t sC33=GetCovariance()[9];
300 if (sC33<=0 || sC33>1.) {
8602c008 301 if (n>fgkWARN) Warning("Invariant","fC33=%f\n",sC33);
6c94f330 302 return kFALSE;
a9a2d814 303 }
6c94f330 304 Double_t sC44=GetCovariance()[14];
305 if (sC44<=0 /*|| sC44>6e-5*/) {
8602c008 306 if (n>fgkWARN) Warning("Invariant","fC44=%f\n",sC44);
6c94f330 307 return kFALSE;
14825d5a 308 }
6c94f330 309
310 return kTRUE;
006b5f7f 311}
312
313//____________________________________________________________________________
6c94f330 314Bool_t AliITStrackV2::Propagate(Double_t alp,Double_t xk) {
006b5f7f 315 //------------------------------------------------------------------
316 //This function propagates a track
317 //------------------------------------------------------------------
6c94f330 318 Double_t bz=GetBz();
319 if (!AliExternalTrackParam::Propagate(alp,xk,bz)) return kFALSE;
006b5f7f 320
006b5f7f 321 if (!Invariant()) {
8a84886c 322 Int_t n=GetNumberOfClusters();
323 if (n>fgkWARN) AliWarning("Wrong invariant !");
324 return kFALSE;
791f9a2a 325 }
326
6c94f330 327 return kTRUE;
a9a2d814 328}
006b5f7f 329
afd25725 330Bool_t AliITStrackV2::MeanBudgetToPrimVertex(Double_t xyz[3], Double_t step, Double_t &d) const {
331
332 //-------------------------------------------------------------------
333 // Get the mean material budget between the actual point and the
334 // primary vertex. (L.Gaudichet)
335 //-------------------------------------------------------------------
336
337 Double_t cs=TMath::Cos(GetAlpha()), sn=TMath::Sin(GetAlpha());
338 Double_t vertexX = xyz[0]*cs + xyz[1]*sn;
339
340 Int_t nstep = Int_t((GetX()-vertexX)/step);
341 if (nstep<1) nstep = 1;
342 step = (GetX()-vertexX)/nstep;
343
c7719399 344 // Double_t mparam[7], densMean=0, radLength=0, length=0;
345 Double_t mparam[7];
afd25725 346 Double_t p1[3], p2[3], x = GetX(), bz = GetBz();
347 GetXYZ(p1);
348
349 d=0.;
350
351 for (Int_t i=0; i<nstep; i++) {
352 x += step;
353 if (!GetXYZAt(x, bz, p2)) return kFALSE;
354 AliTracker::MeanMaterialBudget(p1, p2, mparam);
355 if (mparam[1]>900000) return kFALSE;
356 d += mparam[1];
357
358 p1[0] = p2[0];
359 p1[1] = p2[1];
360 p1[2] = p2[2];
361 }
362
363 return kTRUE;
364}
365
6c94f330 366Bool_t AliITStrackV2::Improve(Double_t x0,Double_t xyz[3],Double_t ers[3]) {
babd135a 367 //------------------------------------------------------------------
6c94f330 368 //This function improves angular track parameters
babd135a 369 //------------------------------------------------------------------
6c94f330 370 Double_t cs=TMath::Cos(GetAlpha()), sn=TMath::Sin(GetAlpha());
371//Double_t xv = xyz[0]*cs + xyz[1]*sn; // vertex
372 Double_t yv =-xyz[0]*sn + xyz[1]*cs; // in the
373 Double_t zv = xyz[2]; // local frame
babd135a 374
6c94f330 375 Double_t dy = Par(0) - yv, dz = Par(1) - zv;
376 Double_t r2=GetX()*GetX() + dy*dy;
6c23ffed 377 Double_t p2=(1.+ GetTgl()*GetTgl())/(GetSigned1Pt()*GetSigned1Pt());
a9a2d814 378 Double_t beta2=p2/(p2 + GetMass()*GetMass());
379 x0*=TMath::Sqrt((1.+ GetTgl()*GetTgl())/(1.- GetSnp()*GetSnp()));
8676d691 380 Double_t theta2=14.1*14.1/(beta2*p2*1e6)*x0;
381 //Double_t theta2=1.0259e-6*14*14/28/(beta2*p2)*x0*9.36*2.33;
6c94f330 382
383 Double_t cnv=GetBz()*kB2C;
a9a2d814 384 {
6c94f330 385 Double_t dummy = 4/r2 - GetC()*GetC();
386 if (dummy < 0) return kFALSE;
387 Double_t parp = 0.5*(GetC()*GetX() + dy*TMath::Sqrt(dummy));
388 Double_t sigma2p = theta2*(1.- GetSnp()*GetSnp())*(1. + GetTgl()*GetTgl());
389 sigma2p += Cov(0)/r2*(1.- dy*dy/r2)*(1.- dy*dy/r2);
390 sigma2p += ers[1]*ers[1]/r2;
391 sigma2p += 0.25*Cov(14)*cnv*cnv*GetX()*GetX();
00709873 392 Double_t eps2p=sigma2p/(Cov(5) + sigma2p);
6c94f330 393 Par(0) += Cov(3)/(Cov(5) + sigma2p)*(parp - GetSnp());
394 Par(2) = eps2p*GetSnp() + (1 - eps2p)*parp;
395 Cov(5) *= eps2p;
396 Cov(3) *= eps2p;
a9a2d814 397 }
398 {
6c94f330 399 Double_t parl=0.5*GetC()*dz/TMath::ASin(0.5*GetC()*TMath::Sqrt(r2));
400 Double_t sigma2l=theta2;
401 sigma2l += Cov(2)/r2 + Cov(0)*dy*dy*dz*dz/(r2*r2*r2);
402 sigma2l += ers[2]*ers[2]/r2;
403 Double_t eps2l = sigma2l/(Cov(9) + sigma2l);
404 Par(1) += Cov(7 )/(Cov(9) + sigma2l)*(parl - Par(3));
405 Par(4) += Cov(13)/(Cov(9) + sigma2l)*(parl - Par(3));
406 Par(3) = eps2l*Par(3) + (1-eps2l)*parl;
407 Cov(9) *= eps2l;
00709873 408 Cov(13)*= eps2l;
6c94f330 409 Cov(7) *= eps2l;
a9a2d814 410 }
6c94f330 411 if (!Invariant()) return kFALSE;
14825d5a 412
6c94f330 413 return kTRUE;
14825d5a 414}
23efe5f1 415
416void AliITStrackV2::CookdEdx(Double_t low, Double_t up) {
417 //-----------------------------------------------------------------
a9a2d814 418 // This function calculates dE/dX within the "low" and "up" cuts.
419 // Origin: Boris Batyunya, JINR, Boris.Batiounia@cern.ch
23efe5f1 420 //-----------------------------------------------------------------
23efe5f1 421 // The clusters order is: SSD-2, SSD-1, SDD-2, SDD-1, SPD-2, SPD-1
c0dd5278 422
423 Int_t i;
424 Int_t nc=0;
425 for (i=0; i<GetNumberOfClusters(); i++) {
426 Int_t idx=GetClusterIndex(i);
427 idx=(idx&0xf0000000)>>28;
428 if (idx>1) nc++; // Take only SSD and SDD
429 }
23efe5f1 430
a9a2d814 431 Int_t swap;//stupid sorting
23efe5f1 432 do {
433 swap=0;
434 for (i=0; i<nc-1; i++) {
435 if (fdEdxSample[i]<=fdEdxSample[i+1]) continue;
436 Float_t tmp=fdEdxSample[i];
437 fdEdxSample[i]=fdEdxSample[i+1]; fdEdxSample[i+1]=tmp;
438 swap++;
439 }
440 } while (swap);
441
a9a2d814 442 Int_t nl=Int_t(low*nc), nu=Int_t(up*nc); //b.b. to take two lowest dEdX
443 // values from four ones choose
444 // nu=2
23efe5f1 445 Float_t dedx=0;
a9a2d814 446 for (i=nl; i<nu; i++) dedx += fdEdxSample[i];
c0dd5278 447 if (nu-nl>0) dedx /= (nu-nl);
23efe5f1 448
23efe5f1 449 SetdEdx(dedx);
450}
c7bafca9 451
6c94f330 452Double_t AliITStrackV2::GetBz() const {
453 //
454 // returns Bz component of the magnetic field (kG)
455 //
456 if (AliTracker::UniformField()) return AliTracker::GetBz();
457 Double_t r[3]; GetXYZ(r);
458 return AliTracker::GetBz(r);
5773defd 459}
6c94f330 460
8602c008 461//____________________________________________________________________________
462Bool_t AliITStrackV2::
e50912db 463GetPhiZat(Double_t r, Double_t &phi, Double_t &z) const {
464 //------------------------------------------------------------------
465 // This function returns the global cylindrical (phi,z) of the track
466 // position estimated at the radius r.
467 // The track curvature is neglected.
468 //------------------------------------------------------------------
469 Double_t d=GetD(0.,0.);
470 if (TMath::Abs(d) > r) return kFALSE;
471
472 Double_t rcurr=TMath::Sqrt(GetX()*GetX() + GetY()*GetY());
473 if (TMath::Abs(d) > rcurr) return kFALSE;
474 Double_t phicurr=GetAlpha()+TMath::ASin(GetSnp());
475
476 phi=phicurr+TMath::ASin(d/r)-TMath::ASin(d/rcurr);
c7de5c65 477 z=GetZ()+GetTgl()*(TMath::Sqrt((r-d)*(r+d))-TMath::Sqrt((rcurr-d)*(rcurr+d)));
e50912db 478 return kTRUE;
479}
480//____________________________________________________________________________
481Bool_t AliITStrackV2::
482GetLocalXat(Double_t r,Double_t &xloc) const {
8602c008 483 //------------------------------------------------------------------
e50912db 484 // This function returns the local x of the track
485 // position estimated at the radius r.
8602c008 486 // The track curvature is neglected.
487 //------------------------------------------------------------------
488 Double_t d=GetD(0.,0.);
e50912db 489 if (TMath::Abs(d) > r) return kFALSE;
8602c008 490
e50912db 491 Double_t rcurr=TMath::Sqrt(GetX()*GetX() + GetY()*GetY());
492 Double_t phicurr=GetAlpha()+TMath::ASin(GetSnp());
493 Double_t phi=phicurr+TMath::ASin(d/r)-TMath::ASin(d/rcurr);
8602c008 494
e50912db 495 xloc=r*(TMath::Cos(phi)*TMath::Cos(GetAlpha())
496 +TMath::Sin(phi)*TMath::Sin(GetAlpha()));
8602c008 497
498 return kTRUE;
499}