HEXPLIT.h

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// SPDX-License-Identifier: LGPL-3.0-or-later
// Copyright (C) 2023 Sebouh Paul
 
// An algorithm for splitting calorimeter hits in overlapping cells into "subhits" based on the relative
// energies of hits on neighboring layers
//
// Author: Sebouh Paul
// Date: 12/04/2023
 
#pragma once
 
#include <DD4hep/Detector.h>
#include <algorithms/algorithm.h>
#include <algorithms/geo.h>
#include <edm4eic/CalorimeterHitCollection.h>
#include <gsl/pointers>
#include <string>      // for basic_string
#include <string_view> // for string_view
#include <vector>
 
#include "HEXPLITConfig.h"
#include "algorithms/interfaces/WithPodConfig.h"
 
namespace eicrecon {
 
using HEXPLITAlgorithm =
    algorithms::Algorithm<algorithms::Input<const edm4eic::CalorimeterHitCollection>,
                          algorithms::Output<edm4eic::CalorimeterHitCollection>>;
 
class HEXPLIT : public HEXPLITAlgorithm, public WithPodConfig<HEXPLITConfig> {
 
public:
  HEXPLIT(std::string_view name)
      : HEXPLITAlgorithm{
            name, {"inputHits"}, {"outputSubcellHits"}, "Split hits into subcell hits"} {}
 
  void init() final;
  void process(const Input&, const Output&) const final;
 
private:
  typedef struct stagger_pattern {
    int SUBCELLS;
    int NEIGHBORS;
    int OVERLAP;
    std::vector<double> neighbor_offsets_x;
    std::vector<double> neighbor_offsets_y;
    std::vector<std::vector<int>> neighbor_indices;
    std::vector<double> subcell_offsets_x;
    std::vector<double> subcell_offsets_y;
  } stagger_pattern;
 
  // number of subcells that a single cell is divided into
  static const int SUBCELLS_H4 = 12;
  // number of neighboring positions whose overlap define the subcells
  static const int NEIGHBORS_H4 = 12;
  // number of neighboring cells that overlap to obtain a subcell
  static const int OVERLAP_H4 = 3;
  //positions where the overlapping cells are relative to a given cell (in units of hexagon side length)
  static const std::vector<double> neighbor_offsets_x_H4;
  static const std::vector<double> neighbor_offsets_y_H4;
  //indices of the neighboring cells which overlap to produce a given subcell
  static const std::vector<std::vector<int>> neighbor_indices_H4;
  //positions of the centers of subcells
  static const std::vector<double> subcell_offsets_x_H4;
  static const std::vector<double> subcell_offsets_y_H4;
 
  const stagger_pattern stag_H4 = {
      .SUBCELLS           = SUBCELLS_H4,
      .NEIGHBORS          = NEIGHBORS_H4,
      .OVERLAP            = OVERLAP_H4,
      .neighbor_offsets_x = neighbor_offsets_x_H4,
      .neighbor_offsets_y = neighbor_offsets_y_H4,
      .neighbor_indices   = neighbor_indices_H4,
      .subcell_offsets_x  = subcell_offsets_x_H4,
      .subcell_offsets_y  = subcell_offsets_y_H4,
  };
 
  static const int SUBCELLS_S2 = 4;
  // number of neighboring positions whose overlap define the subcells
  static const int NEIGHBORS_S2 = 4;
  // number of neighboring cells that overlap to obtain a subcell
  static const int OVERLAP_S2 = 1;
  //positions where the overlapping cells are relative to a given cell (in units of hexagon side length)
  static const std::vector<double> neighbor_offsets_x_S2;
  static const std::vector<double> neighbor_offsets_y_S2;
  //indices of the neighboring cells which overlap to produce a given subcell
  static const std::vector<std::vector<int>> neighbor_indices_S2;
  //positions of the centers of subcells
  static const std::vector<double> subcell_offsets_x_S2;
  static const std::vector<double> subcell_offsets_y_S2;
 
  const stagger_pattern stag_S2 = {
      .SUBCELLS           = SUBCELLS_S2,
      .NEIGHBORS          = NEIGHBORS_S2,
      .OVERLAP            = OVERLAP_S2,
      .neighbor_offsets_x = neighbor_offsets_x_S2,
      .neighbor_offsets_y = neighbor_offsets_y_S2,
      .neighbor_indices   = neighbor_indices_S2,
      .subcell_offsets_x  = subcell_offsets_x_S2,
      .subcell_offsets_y  = subcell_offsets_y_S2,
  };
 
  stagger_pattern stag = stag_H4;
 
private:
  const dd4hep::Detector* m_detector{algorithms::GeoSvc::instance().detector()};
};
 
} // namespace eicrecon