GaussianGridTrackDensity.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2020 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once
#include "Acts/EventData/TrackParameters.hpp"
#include "Acts/Utilities/Definitions.hpp"
#include "Acts/Utilities/Result.hpp"

namespace Acts {
template <int mainGridSize = 2000, int trkGridSize = 15>
class GaussianGridTrackDensity {
  // Assert odd trkGridSize
  static_assert(trkGridSize % 2);
  // Assert bigger main grid than track grid
  static_assert(mainGridSize > trkGridSize);

 public:
  struct Config {
    Config(float zMinMax_ = 100) : zMinMax(zMinMax_) {
      binSize = 2. * zMinMax / mainGridSize;
    }
    // Min and max z value of big grid
    float zMinMax;  // mm

    // Z size of one single bin in grid
    float binSize;  // mm

    // Do NOT use just the z-bin with the highest
    // track density, but instead check the (up to)
    // first three density maxima (only those that have
    // a maximum relative deviation of 'relativeDensityDev'
    // from the main maximum) and take the z-bin of the
    // maximum with the highest surrounding density sum
    bool useHighestSumZPosition = false;

    // The maximum relative density deviation from the main
    // maximum to consider the second and third maximum for
    // the highest-sum approach from above
    float maxRelativeDensityDev = 0.01;
  };

  GaussianGridTrackDensity(const Config& cfg) : m_cfg(cfg) {}

  Result<float> getMaxZPosition(ActsVectorF<mainGridSize>& mainGrid) const;

  Result<std::pair<float, float>> getMaxZPositionAndWidth(
      ActsVectorF<mainGridSize>& mainGrid) const;

  std::pair<int, ActsVectorF<trkGridSize>> addTrack(
      const BoundTrackParameters& trk,
      ActsVectorF<mainGridSize>& mainGrid) const;

  void removeTrackGridFromMainGrid(int zBin,
                                   const ActsVectorF<trkGridSize>& trkGrid,
                                   ActsVectorF<mainGridSize>& mainGrid) const;

 private:
  void addTrackGridToMainGrid(int zBin, const ActsVectorF<trkGridSize>& trkGrid,
                              ActsVectorF<mainGridSize>& mainGrid) const;

  void modifyMainGridWithTrackGrid(int zBin,
                                   const ActsVectorF<trkGridSize>& trkGrid,
                                   ActsVectorF<mainGridSize>& mainGrid,
                                   int modifyModeSign) const;

  ActsVectorF<trkGridSize> createTrackGrid(int offset, const SymMatrix2D& cov,
                                           float distCtrD,
                                           float distCtrZ) const;

  Result<float> estimateSeedWidth(ActsVectorF<mainGridSize>& mainGrid,
                                  float maxZ) const;

  float normal2D(float d, float z, const SymMatrix2D& cov) const;

  int getHighestSumZPosition(ActsVectorF<mainGridSize>& mainGrid) const;

  double getDensitySum(const ActsVectorF<mainGridSize>& mainGrid,
                       int pos) const;

  Config m_cfg;
};

}  // namespace Acts

#include "Acts/Vertexing/GaussianGridTrackDensity.ipp"