Add TrackerACTS header for ACTS-based tracking

Author: njacazio

Detectors/Upgrades/ALICE3/TRK/reconstruction/include/TRKReconstruction/TrackerACTS.h

@@ -0,0 +1,189 @@
+// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+///
+/// \file TrackerACTS.h
+/// \brief TRK tracker using ACTS seeding algorithm
+/// \author Nicolò Jacazio, Università del Piemonte Orientale (IT)
+/// \since 2026-04-01
+///
+
+#ifndef ALICE3_INCLUDE_TRACKERACTS_H_
+#define ALICE3_INCLUDE_TRACKERACTS_H_
+
+#include "Acts/Definitions/Units.hpp"
+#include "Framework/Logger.h"
+
+#include "ITStracking/TimeFrame.h"
+#include "TH2F.h"
+
+namespace o2::trk
+{
+
+/// Configuration for the ACTS-based tracker
+struct TrackerACTSConfig {
+  // Seeding parameters
+  float minPt = 0.4f * Acts::UnitConstants::GeV;             ///< Minimum pT for seeds
+  float maxImpactParameter = 10.f * Acts::UnitConstants::mm; ///< Maximum impact parameter
+  float cotThetaMax = std::sinh(4.0f);                       ///< Maximum cot(theta), corresponds to eta ~4
+
+  // Delta R cuts for doublet/triplet formation
+  float deltaRMinBottom = 5.f * Acts::UnitConstants::mm;   ///< Min deltaR for bottom-middle
+  float deltaRMaxBottom = 200.f * Acts::UnitConstants::mm; ///< Max deltaR for bottom-middle
+  float deltaRMinTop = 5.f * Acts::UnitConstants::mm;      ///< Min deltaR for middle-top
+  float deltaRMaxTop = 200.f * Acts::UnitConstants::mm;    ///< Max deltaR for middle-top
+
+  // Z cuts
+  float zMin = -3000.f * Acts::UnitConstants::mm;
+  float zMax = 3000.f * Acts::UnitConstants::mm;
+
+  // Collision region
+  float collisionRegionMin = -150.f * Acts::UnitConstants::mm;
+  float collisionRegionMax = 150.f * Acts::UnitConstants::mm;
+
+  // Quality cuts
+  float maxSeedsPerMiddleSP = 2;
+  float deltaPhiMax = 0.1f; ///< Maximum phi difference for doublets
+};
+
+/// Space point representation for tracking
+struct SpacePoint {
+  float x{0.f};
+  float y{0.f};
+  float z{0.f};
+  int layer{-1};
+  int clusterId{-1};
+  int rof{-1};
+
+  // Derived quantities
+  float r() const { return std::hypot(x, y); }
+  float radius() const { return r(); } // required by Acts::CylindricalGridElement concept
+  float phi() const { return std::atan2(y, x); }
+
+  // Variance estimates (can be refined based on cluster properties)
+  float varianceR{0.01f}; // ~100 um resolution squared
+  float varianceZ{0.01f};
+};
+
+/// Seed (triplet of space points)
+struct SeedACTS {
+  const SpacePoint* bottom{nullptr};
+  const SpacePoint* middle{nullptr};
+  const SpacePoint* top{nullptr};
+  float quality{0.f};
+};
+
+/// TRK Tracker using ACTS algorithms for seeding and track finding
+template <int nLayers>
+class TrackerACTS
+{
+ public:
+  TrackerACTS();
+  ~TrackerACTS()
+  {
+    if (mHistSpacePoints) {
+      mHistSpacePoints->SaveAs("/tmp/mHistSpacePoints.C");
+      delete mHistSpacePoints;
+      mHistSpacePoints = nullptr;
+    }
+  }
+
+  /// Adopt a TimeFrame for processing
+  void adoptTimeFrame(o2::its::TimeFrame<nLayers>& tf);
+
+  /// Main tracking entry point: convert clusters to tracks
+  void clustersToTracks();
+
+  /// Configuration
+  void setConfig(const TrackerACTSConfig& cfg) { mConfig = cfg; }
+  TrackerACTSConfig& getConfig() { return mConfig; }
+  const TrackerACTSConfig& getConfig() const { return mConfig; }
+
+  /// Set the magnetic field strength
+  void setBz(float bz) { mBz = bz; }
+
+  /// Get the magnetic field strength
+  float getBz() const { return mBz; }
+
+  /// Print tracking summary
+  void printSummary() const;
+
+ private:
+  TH2F* mHistSpacePoints = nullptr;
+
+  /// Build space points from clusters in the TimeFrame
+  void buildSpacePoints(int rof);
+
+  /// Create seeds (triplets) from space points using ACTS SeedFinder
+  void createSeeds();
+
+  /// Estimate track parameters from a seed using ACTS
+  bool estimateTrackParams(const SeedACTS& seed, o2::its::TrackITSExt& track) const;
+
+  /// Run track finding from seeds
+  void findTracks();
+
+  /// Assign MC labels to tracks
+  void computeTracksMClabels();
+
+  /// Helper: time a task
+  template <typename Func>
+  float evaluateTask(Func&& task, std::string_view taskName);
+
+  // Configuration
+  TrackerACTSConfig mConfig;
+
+  // TimeFrame data
+  o2::its::TimeFrame<nLayers>* mTimeFrame = nullptr;
+
+  // Space points built from clusters
+  std::vector<SpacePoint> mSpacePoints;
+  std::vector<std::vector<const SpacePoint*>> mSpacePointsPerLayer;
+
+  // Seeds
+  std::vector<SeedACTS> mSeeds;
+
+  // Tracking state
+  float mBz{0.5f}; ///< Magnetic field in Tesla
+  unsigned int mTimeFrameCounter{0};
+  double mTotalTime{0.};
+
+  // Tracking states for logging
+  enum State {
+    SpacePointBuilding = 0,
+    Seeding,
+    TrackFinding,
+    NStates,
+  };
+  State mCurState{SpacePointBuilding};
+  static constexpr std::array<const char*, NStates> StateNames{
+    "Space point building",
+    "ACTS seeding",
+    "Track finding"};
+};
+
+template <int nLayers>
+template <typename Func>
+float TrackerACTS<nLayers>::evaluateTask(Func&& task, std::string_view taskName)
+{
+  LOG(debug) << " + Starting " << taskName;
+  const auto start = std::chrono::high_resolution_clock::now();
+  task();
+  const auto end = std::chrono::high_resolution_clock::now();
+  std::chrono::duration<double, std::milli> diff{end - start};
+
+  LOG(debug) << " - " << taskName << " completed in: " << std::fixed << std::setprecision(2) << diff.count() << " ms";
+  return static_cast<float>(diff.count());
+}
+
+} // namespace o2::trk
+
+#endif /* ALICE3_INCLUDE_TRACKERACTS_H_ */