From b8b98dc222e96ece2926e6d5a3fec7d6e3d690a3 Mon Sep 17 00:00:00 2001
From: mivanov <marian.ivanov@cern.ch>
Date: Wed, 12 Feb 2014 14:56:42 +0100
Subject: [PATCH] STEER/STEERBase/AliExternalTrackParam.h,cxx  - getter to
 acces information also in TTree::Draw

---
 STEER/STEERBase/AliExternalTrackParam.cxx | 66 +++++++++++++++++++++++
 STEER/STEERBase/AliExternalTrackParam.h   |  2 +
 2 files changed, 68 insertions(+)

diff --git a/STEER/STEERBase/AliExternalTrackParam.cxx b/STEER/STEERBase/AliExternalTrackParam.cxx
index e9e8af95386..fc28c06ca2d 100644
--- a/STEER/STEERBase/AliExternalTrackParam.cxx
+++ b/STEER/STEERBase/AliExternalTrackParam.cxx
@@ -2657,3 +2657,69 @@ Bool_t AliExternalTrackParam::GetXYZatR(Double_t xr,Double_t bz, Double_t *xyz,
   return kTRUE;  
   //
 }
+
+
+Double_t  AliExternalTrackParam::GetParameterAtRadius(Double_t r, Double_t bz, Int_t parType) const
+{
+  //
+  // Get track parameters at the radius of interest.
+  // Given function is aimed to be used to interactivelly (tree->Draw())
+  // access track properties at different radii
+  //
+  // TO BE USED WITH SPECICAL CARE - 
+  //     it is aimed to be used for rough calculation as constant field and  
+  //     no correction for material is used
+  //  
+  // r  - radius of interest
+  // bz - magentic field 
+  // retun values dependens on parType:
+  //    parType = 0  -gx 
+  //    parType = 1  -gy 
+  //    parType = 2  -gz 
+  //
+  //    parType = 3  -pgx 
+  //    parType = 4  -pgy 
+  //    parType = 5  -pgz
+  //
+  //    parType = 6  - r
+  //    parType = 7  - global position phi
+  //    parType = 8  - global direction phi
+  //    parType = 9  - direction phi- positionphi
+  if (parType<0) {
+    parType=-1;
+     return 0;
+  }
+  Double_t xyz[3];
+  Double_t pxyz[3];  
+  Double_t localX=0;
+  Bool_t res = GetXatLabR(r,localX,bz,1);
+  if (!res) {
+    parType=-1;
+    return 0;
+  }
+  //
+  // position parameters
+  // 
+  GetXYZAt(localX,bz,xyz); 
+  if (parType<3)   {
+    return xyz[parType];
+  }
+
+  if (parType==6) return TMath::Sqrt(xyz[0]*xyz[0]+xyz[1]*xyz[1]);
+  if (parType==7) return TMath::ATan2(xyz[1],xyz[0]);
+  //
+  // momenta parameters
+  //
+  GetPxPyPzAt(localX,bz,pxyz); 
+  if (parType==8) return TMath::ATan2(pxyz[1],pxyz[0]);
+  if (parType==9) {
+    Double_t diff = TMath::ATan2(pxyz[1],pxyz[0])-TMath::ATan2(xyz[1],xyz[0]);
+    if (diff>TMath::Pi()) diff-=TMath::TwoPi();
+    if (diff<-TMath::Pi()) diff+=TMath::TwoPi();
+    return diff;
+  }
+  if (parType>=3&&parType<6) {
+    return pxyz[parType%3];
+  }
+  return 0;
+}
diff --git a/STEER/STEERBase/AliExternalTrackParam.h b/STEER/STEERBase/AliExternalTrackParam.h
index d3ad96091c4..e087bbf9f65 100644
--- a/STEER/STEERBase/AliExternalTrackParam.h
+++ b/STEER/STEERBase/AliExternalTrackParam.h
@@ -213,6 +213,8 @@ class AliExternalTrackParam: public AliVTrack {
   Bool_t GetCovarianceXYZPxPyPz(Double_t cv[21]) const;
   Bool_t GetPxPyPzAt(Double_t x, Double_t b, Double_t p[3]) const;
   Bool_t GetXYZAt(Double_t x, Double_t b, Double_t r[3]) const;
+  Double_t GetParameterAtRadius(Double_t r, Double_t bz, Int_t parType) const;
+
   Bool_t GetYAt(Double_t x,  Double_t b,  Double_t &y) const;
   Bool_t GetZAt(Double_t x,  Double_t b,  Double_t &z) const;
   void Print(Option_t* option = "") const;
-- 
2.39.3