ITS: buildSeeds check only once of b=0

Signed-off-by: Felix Schlepper <felix.schlepper@cern.ch>

Author: f3sch

Detectors/ITSMFT/ITS/tracking/include/ITStracking/TrackerTraits.h

@@ -90,8 +90,6 @@ class TrackerTraits
   virtual int getTFNumberOfTracklets() const { return mTimeFrame->getNumberOfTracklets(); }
   virtual int getTFNumberOfCells() const { return mTimeFrame->getNumberOfCells(); }
 
-  float mBz = 5.f;
-
  private:
   track::TrackParCov buildTrackSeed(const Cluster& cluster1, const Cluster& cluster2, const TrackingFrameInfo& tf3);
   bool fitTrack(TrackITSExt& track, int start, int end, int step, float chi2clcut = o2::constants::math::VeryBig, float chi2ndfcut = o2::constants::math::VeryBig, float maxQoverPt = o2::constants::math::VeryBig, int nCl = 0);
@@ -106,6 +104,9 @@ class TrackerTraits
   o2::gpu::GPUChainITS* mChain = nullptr;
   TimeFrame<nLayers>* mTimeFrame;
   std::vector<TrackingParameters> mTrkParams;
+
+  float mBz{-999.f};
+  bool mIsZeroField{false};
 };
 
 template <int nLayers>

Detectors/ITSMFT/ITS/tracking/src/TrackerTraits.cxx

@@ -1235,7 +1235,8 @@ bool TrackerTraits<nLayers>::trackFollowing(TrackITSExt* track, int rof, bool ou
 template <int nLayers>
 track::TrackParCov TrackerTraits<nLayers>::buildTrackSeed(const Cluster& cluster1, const Cluster& cluster2, const TrackingFrameInfo& tf3)
 {
-  const float ca = o2::gpu::CAMath::Cos(tf3.alphaTrackingFrame), sa = o2::gpu::CAMath::Sin(tf3.alphaTrackingFrame);
+  float ca{-999.f}, sa{-999.f};
+  o2::gpu::CAMath::SinCos(tf3.alphaTrackingFrame, sa, ca);
   const float x1 = cluster1.xCoordinate * ca + cluster1.yCoordinate * sa;
   const float y1 = -cluster1.xCoordinate * sa + cluster1.yCoordinate * ca;
   const float z1 = cluster1.zCoordinate;
@@ -1245,29 +1246,27 @@ track::TrackParCov TrackerTraits<nLayers>::buildTrackSeed(const Cluster& cluster
   const float x3 = tf3.xTrackingFrame;
   const float y3 = tf3.positionTrackingFrame[0];
   const float z3 = tf3.positionTrackingFrame[1];
-
-  const bool zeroField{std::abs(getBz()) < o2::constants::math::Almost0};
-  const float tgp = zeroField ? o2::gpu::CAMath::ATan2(y3 - y1, x3 - x1) : 1.f;
-  const float crv = zeroField ? 1.f : math_utils::computeCurvature(x3, y3, x2, y2, x1, y1);
-  const float snp = zeroField ? tgp / o2::gpu::CAMath::Sqrt(1.f + tgp * tgp) : crv * (x3 - math_utils::computeCurvatureCentreX(x3, y3, x2, y2, x1, y1));
-  const float tgl12 = math_utils::computeTanDipAngle(x1, y1, x2, y2, z1, z2);
-  const float tgl23 = math_utils::computeTanDipAngle(x2, y2, x3, y3, z2, z3);
-  const float q2pt = zeroField ? 1.f / o2::track::kMostProbablePt : crv / (getBz() * o2::constants::math::B2C);
-  const float q2pt2 = crv * crv;
-  const float sg2q2pt = track::kC1Pt2max * (q2pt2 > 0.0005 ? (q2pt2 < 1 ? q2pt2 : 1) : 0.0005);
-  return track::TrackParCov(tf3.xTrackingFrame, tf3.alphaTrackingFrame,
-                            {y3, z3, snp, 0.5f * (tgl12 + tgl23), q2pt},
-                            {tf3.covarianceTrackingFrame[0],
-                             tf3.covarianceTrackingFrame[1], tf3.covarianceTrackingFrame[2],
-                             0.f, 0.f, track::kCSnp2max,
-                             0.f, 0.f, 0.f, track::kCTgl2max,
-                             0.f, 0.f, 0.f, 0.f, sg2q2pt});
+  float tgp{1.f}, crv{1.f}, snp{-999.f}, tgl12{-999.f}, tgl23{-999.f}, q2pt{1.f / track::kMostProbablePt}, q2pt2{1.f}, sg2q2pt{-999.f};
+  if (mIsZeroField) {
+    tgp = o2::gpu::CAMath::ATan2(y3 - y1, x3 - x1);
+    snp = tgp / o2::gpu::CAMath::Sqrt(1.f + tgp * tgp);
+  } else {
+    crv = math_utils::computeCurvature(x3, y3, x2, y2, x1, y1);
+    snp = crv * (x3 - math_utils::computeCurvatureCentreX(x3, y3, x2, y2, x1, y1));
+    q2pt = crv / (mBz * o2::constants::math::B2C);
+    q2pt2 = crv * crv;
+  }
+  tgl12 = math_utils::computeTanDipAngle(x1, y1, x2, y2, z1, z2);
+  tgl23 = math_utils::computeTanDipAngle(x2, y2, x3, y3, z2, z3);
+  sg2q2pt = track::kC1Pt2max * (q2pt2 > 0.0005f ? (q2pt2 < 1.f ? q2pt2 : 1.f) : 0.0005f);
+  return {tf3.xTrackingFrame, tf3.alphaTrackingFrame, {y3, z3, snp, 0.5f * (tgl12 + tgl23), q2pt}, {tf3.covarianceTrackingFrame[0], tf3.covarianceTrackingFrame[1], tf3.covarianceTrackingFrame[2], 0.f, 0.f, track::kCSnp2max, 0.f, 0.f, 0.f, track::kCTgl2max, 0.f, 0.f, 0.f, 0.f, sg2q2pt}};
 }
 
 template <int nLayers>
 void TrackerTraits<nLayers>::setBz(float bz)
 {
   mBz = bz;
+  mIsZeroField = std::abs(mBz) < 0.01;
   mTimeFrame->setBz(bz);
 }