SpacePointHit3DBuilder_tool.cc

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/**
 *  @file   SpacePointHit3DBuilder_tool.cc
 *
 *  @brief  This tool provides "standard" 3D hits built (by this tool) from 2D hits
 *
 */

// Framework Includes
#include "art/Framework/Core/ProducesCollector.h"
#include "art/Framework/Principal/Event.h"
#include "art/Framework/Principal/Handle.h"
#include "art/Framework/Services/Registry/ServiceHandle.h"
#include "art/Persistency/Common/PtrMaker.h"
#include "art/Utilities/ToolMacros.h"
#include "art_root_io/TFileService.h"
#include "canvas/Persistency/Common/Assns.h"
#include "canvas/Persistency/Common/Ptr.h"
#include "canvas/Utilities/InputTag.h"
#include "cetlib/cpu_timer.h"
#include "fhiclcpp/ParameterSet.h"
#include "messagefacility/MessageLogger/MessageLogger.h"

// LArSoft includes
#include "larcore/Geometry/Geometry.h"
#include "larcoreobj/SimpleTypesAndConstants/geo_types.h"
#include "lardata/ArtDataHelper/HitCreator.h"
#include "lardata/DetectorInfoServices/DetectorClocksService.h"
#include "lardata/DetectorInfoServices/DetectorPropertiesService.h"
#include "lardataalg/DetectorInfo/DetectorProperties.h"
#include "lardataobj/RecoBase/Hit.h"
#include "lardataobj/RecoBase/SpacePoint.h"
#include "larreco/RecoAlg/Cluster3DAlgs/Cluster3D.h"
#include "larreco/RecoAlg/Cluster3DAlgs/IHit3DBuilder.h"

// std includes
#include <cmath>
#include <iostream>
#include <map>
#include <memory>
#include <unordered_map>
#include <utility>
#include <vector>
#include <numeric> // std::accumulate

// Ack!
#include "TTree.h"

//------------------------------------------------------------------------------------------------------------------------------------------
// implementation follows

namespace lar_cluster3d {

  /**
 *  @brief  SpacePointHit3DBuilder class definiton
 */
  class SpacePointHit3DBuilder : virtual public IHit3DBuilder {
  public:
    /**
     *  @brief  Constructor
     *
     *  @param  pset
     */
    explicit SpacePointHit3DBuilder(fhicl::ParameterSet const& pset);

    /**
     *  @brief  Destructor
     */
    ~SpacePointHit3DBuilder();

    /**
     *  @brief Each algorithm may have different objects it wants "produced" so use this to
     *         let the top level producer module "know" what it is outputting
     */
    virtual void produces(art::ProducesCollector&) override;

    void configure(const fhicl::ParameterSet&) override;

    /**
     *  @brief Given a set of recob hits, run DBscan to form 3D clusters
     *
     *  @param hitPairList           The input list of 3D hits to run clustering on
     *  @param clusterParametersList A list of cluster objects (parameters from associated hits)
     */
    void Hit3DBuilder(art::Event& evt, reco::HitPairList& hitPairList, RecobHitToPtrMap&) override;

    /**
     *  @brief If monitoring, recover the time to execute a particular function
     */
    float
    getTimeToExecute(IHit3DBuilder::TimeValues index) const override
    {
      return fTimeVector.at(index);
    }

  private:
    /**
     *  @brief clear the tuple vectors before processing next event
     */
    void clear();

    /**
     * @brief Perform charge integration between limits
     */
    float chargeIntegral(float, float, float, float, int, int) const;

    using Hit2DVector = std::vector<reco::ClusterHit2D>;

    /**
     *  @brief Data members to follow
     */
    art::InputTag fSpacePointProducerLabel;
    art::InputTag fHitProducerLabel;
    bool fDoWireAssns;
    bool fDoRawDigitAssns;
    float m_maxHit3DChiSquare; ///< Provide ability to select hits based on "chi square"
    bool m_outputHistograms;   ///< Take the time to create and fill some histograms for diagnostics

    bool fEnableMonitoring;                 ///<
    mutable std::vector<float> fTimeVector; ///<

    // Define some basic histograms
    TTree* m_tupleTree; ///< output analysis tree

    mutable std::vector<float> m_deltaTimeVec;
    mutable std::vector<float> m_chiSquare3DVec;
    mutable std::vector<float> m_maxPullVec;
    mutable std::vector<float> m_overlapFractionVec;
    mutable std::vector<float> m_overlapRangeVec;
    mutable std::vector<float> m_maxSideVecVec;
    mutable std::vector<float> m_pairWireDistVec;
    mutable std::vector<float> m_smallChargeDiffVec;
    mutable std::vector<int> m_smallIndexVec;
    mutable std::vector<float> m_qualityMetricVec;
    mutable std::vector<float> m_spacePointChargeVec;
    mutable std::vector<float> m_hitAsymmetryVec;

    // Get instances of the primary data structures needed
    mutable Hit2DVector m_clusterHit2DMasterVec;

    const geo::Geometry* fGeometry;
  };

  SpacePointHit3DBuilder::SpacePointHit3DBuilder(fhicl::ParameterSet const& pset)
  {
    this->configure(pset);
  }

  //------------------------------------------------------------------------------------------------------------------------------------------

  SpacePointHit3DBuilder::~SpacePointHit3DBuilder() {}

  void
  SpacePointHit3DBuilder::produces(art::ProducesCollector& collector)
  {
    collector.produces<std::vector<recob::Hit>>();

    if (fDoWireAssns) collector.produces<art::Assns<recob::Wire, recob::Hit>>();
    if (fDoRawDigitAssns) collector.produces<art::Assns<raw::RawDigit, recob::Hit>>();
  }

  //------------------------------------------------------------------------------------------------------------------------------------------

  void
  SpacePointHit3DBuilder::configure(fhicl::ParameterSet const& pset)
  {
    fSpacePointProducerLabel = pset.get<art::InputTag>("SpacePointProducerLabel");
    fHitProducerLabel = pset.get<art::InputTag>("HitProducerLabel");
    fDoWireAssns = pset.get<bool>("DoWireAssns", true);
    fDoRawDigitAssns = pset.get<bool>("DoRawDigitAssns", true);
    fEnableMonitoring = pset.get<bool>("EnableMonitoring", true);
    m_maxHit3DChiSquare = pset.get<float>("MaxHitChiSquare", 6.0);
    m_outputHistograms = pset.get<bool>("OutputHistograms", false);

    // Access ART's TFileService, which will handle creating and writing
    // histograms and n-tuples for us.
    art::ServiceHandle<art::TFileService> tfs;

    if (m_outputHistograms) {
      m_tupleTree = tfs->make<TTree>("Hit3DBuilderTree", "Tree by StandardHit3DBuilder");

      clear();

      m_tupleTree->Branch("DeltaTime2D", "std::vector<float>", &m_deltaTimeVec);
      m_tupleTree->Branch("ChiSquare3D", "std::vector<float>", &m_chiSquare3DVec);
      m_tupleTree->Branch("MaxPullValue", "std::vector<float>", &m_maxPullVec);
      m_tupleTree->Branch("OverlapFraction", "std::vector<float>", &m_overlapFractionVec);
      m_tupleTree->Branch("OverlapRange", "std::vector<float>", &m_overlapRangeVec);
      m_tupleTree->Branch("MaxSideVec", "std::vector<float>", &m_maxSideVecVec);
      m_tupleTree->Branch("PairWireDistVec", "std::vector<float>", &m_pairWireDistVec);
      m_tupleTree->Branch("SmallChargeDiff", "std::vector<float>", &m_smallChargeDiffVec);
      m_tupleTree->Branch("SmallChargeIdx", "std::vector<int>", &m_smallIndexVec);
      m_tupleTree->Branch("QualityMetric", "std::vector<float>", &m_qualityMetricVec);
      m_tupleTree->Branch("SPCharge", "std::vector<float>", &m_spacePointChargeVec);
      m_tupleTree->Branch("HitAsymmetry", "std::vector<float>", &m_hitAsymmetryVec);
    }

    fGeometry = art::ServiceHandle<geo::Geometry const>().get();
  }

  void
  SpacePointHit3DBuilder::clear()
  {
    m_deltaTimeVec.clear();
    m_chiSquare3DVec.clear();
    m_maxPullVec.clear();
    m_overlapFractionVec.clear();
    m_overlapRangeVec.clear();
    m_maxSideVecVec.clear();
    m_pairWireDistVec.clear();
    m_smallChargeDiffVec.clear();
    m_smallIndexVec.clear();
    m_qualityMetricVec.clear();
    m_spacePointChargeVec.clear();
    m_hitAsymmetryVec.clear();

    return;
  }

  void
  SpacePointHit3DBuilder::Hit3DBuilder(art::Event& evt,
                                       reco::HitPairList& hitPairList,
                                       RecobHitToPtrMap& recobHitToArtPtrMap)
  {
    /**
     *  @brief Recover the 2D hits from art and fill out the local data structures for the 3D clustering
     */

    fTimeVector.resize(NUMTIMEVALUES, 0.);

    cet::cpu_timer theClockMakeHits;

    if (fEnableMonitoring) theClockMakeHits.start();

    // Start by recovering the associations between space points and hits
    art::Handle<art::Assns<recob::Hit, recob::SpacePoint>> hitSpacePointAssnsHandle;
    evt.getByLabel(fSpacePointProducerLabel, hitSpacePointAssnsHandle);

    if (!hitSpacePointAssnsHandle.isValid()) return;

    // Get a hit refiner for the output hit collection
    recob::HitRefinerAssociator hitRefiner(evt, fHitProducerLabel, fDoWireAssns, fDoRawDigitAssns);

    // We need to spin through the associations first to build a map between the SpacePoints and
    // the WireID associated to the collection plane... where for APA style TPCs this will be
    // unambiguous (note that this is not true for ICARUS!)
    using SpacePointToWireIDMap = std::unordered_map<const recob::SpacePoint*, geo::WireID>;

    SpacePointToWireIDMap spacePointToWireIDMap;

    for (const auto& assnPair : *hitSpacePointAssnsHandle) {
      if (assnPair.first->SignalType() == geo::kCollection)
        spacePointToWireIDMap[assnPair.second.get()] = assnPair.first->WireID();
    }

    // First step is to loop through and get a mapping between space points and associated hits
    // and, importantly, a list of unique hits (and mapping between art ptr and hit)
    using OldHitToNewHitMap = std::map<const recob::Hit*, const recob::Hit*>;
    using SpacePointHitVecMap = std::map<const recob::SpacePoint*, std::vector<const recob::Hit*>>;

    OldHitToNewHitMap oldHitToNewHitMap;
    SpacePointHitVecMap spacePointHitVecMap;

    // We need a container for our new hits...
    std::unique_ptr<std::vector<recob::Hit>> newHitVecPtr(new std::vector<recob::Hit>);

    // reserve a chunk of memory... cannot be more hits than 3 x # spacer points...
    newHitVecPtr->reserve(3 * hitSpacePointAssnsHandle->size());

    // Use this handy art utility to make art::Ptr objects to the new recob::Hits for use in the output phase
    art::PtrMaker<recob::Hit> ptrMaker(evt);

    for (auto& assnPair : *hitSpacePointAssnsHandle) {
      const art::Ptr<recob::SpacePoint> spacePoint = assnPair.second;
      const art::Ptr<recob::Hit>& recobHit = assnPair.first;

      // If we have seen this hit before then no need to create new hit
      if (oldHitToNewHitMap.find(recobHit.get()) == oldHitToNewHitMap.end()) {
        // Recover the reference WireID from our previous map
        geo::WireID refWireID = spacePointToWireIDMap[spacePoint.get()];
        geo::WireID thisWireID = recobHit.get()->WireID();

        // Recover the list of possible WireIDs from the geometry service
        const std::vector<geo::WireID>& wireIDs =
          fGeometry->ChannelToWire(recobHit.get()->Channel());

        // Loop to find match
        for (const auto& wireID : wireIDs) {
          if (wireID.TPC != refWireID.TPC || wireID.Cryostat != refWireID.Cryostat) continue;
          thisWireID = wireID;
          break;
        }

        // Create and save the new recob::Hit with the correct WireID
        newHitVecPtr->emplace_back(recob::HitCreator(*recobHit.get(), thisWireID).copy());

        // Recover a pointer to it...
        recob::Hit* newHit = &newHitVecPtr->back();

        spacePointHitVecMap[spacePoint.get()].push_back(newHit);

        recobHitToArtPtrMap[newHit] = ptrMaker(newHitVecPtr->size() - 1);
        oldHitToNewHitMap[recobHit.get()] = newHit;
      }
      else
        spacePointHitVecMap[spacePoint.get()].push_back(oldHitToNewHitMap[recobHit.get()]);
    }

    // We'll want to correct the hit times for the plane offsets
    // (note this is already taken care of when converting to position)
    std::map<geo::PlaneID, double> planeOffsetMap;

    auto const clock_data =
      art::ServiceHandle<detinfo::DetectorClocksService const>()->DataFor(evt);
    auto const det_prop =
      art::ServiceHandle<detinfo::DetectorPropertiesService const>()->DataFor(evt, clock_data);

    // Initialize the plane to hit vector map
    for (size_t cryoIdx = 0; cryoIdx < fGeometry->Ncryostats(); cryoIdx++) {
      for (size_t tpcIdx = 0; tpcIdx < fGeometry->NTPC(); tpcIdx++) {
        // What we want here are the relative offsets between the planes
        // Note that plane 0 is assumed the "first" plane and is the reference
        planeOffsetMap[geo::PlaneID(cryoIdx, tpcIdx, 0)] = 0.;
        planeOffsetMap[geo::PlaneID(cryoIdx, tpcIdx, 1)] =
          det_prop.GetXTicksOffset(geo::PlaneID(cryoIdx, tpcIdx, 1)) -
          det_prop.GetXTicksOffset(geo::PlaneID(cryoIdx, tpcIdx, 0));
        planeOffsetMap[geo::PlaneID(cryoIdx, tpcIdx, 2)] =
          det_prop.GetXTicksOffset(geo::PlaneID(cryoIdx, tpcIdx, 2)) -
          det_prop.GetXTicksOffset(geo::PlaneID(cryoIdx, tpcIdx, 0));

        std::cout << "***> plane 0 offset: " << planeOffsetMap[geo::PlaneID(cryoIdx, tpcIdx, 0)]
                  << ", plane 1: " << planeOffsetMap[geo::PlaneID(cryoIdx, tpcIdx, 1)]
                  << ", plane 2: " << planeOffsetMap[geo::PlaneID(cryoIdx, tpcIdx, 2)] << std::endl;
        std::cout << "     Det prop plane 0: "
                  << det_prop.GetXTicksOffset(geo::PlaneID(cryoIdx, tpcIdx, 0))
                  << ", plane 1: " << det_prop.GetXTicksOffset(geo::PlaneID(cryoIdx, tpcIdx, 1))
                  << ", plane 2: " << det_prop.GetXTicksOffset(geo::PlaneID(cryoIdx, tpcIdx, 2))
                  << ", Trig: " << trigger_offset(clock_data) << std::endl;
      }
    }

    // We need temporary mapping from recob::Hit's to our 2D hits
    using RecobHitTo2DHitMap = std::map<const recob::Hit*, const reco::ClusterHit2D*>;

    RecobHitTo2DHitMap recobHitTo2DHitMap;

    // Set the size of the container for our hits
    m_clusterHit2DMasterVec.clear();
    m_clusterHit2DMasterVec.reserve(oldHitToNewHitMap.size());

    // Now go throught the list of unique hits and create the 2D hits we'll use
    for (auto& hitPair : oldHitToNewHitMap) {
      const recob::Hit* recobHit = hitPair.second;
      const geo::WireID& hitWireID(recobHit->WireID());

      double hitPeakTime(
        recobHit->PeakTime() -
        planeOffsetMap.at(hitWireID.planeID())); //planeOffsetMap[hitWireID.planeID()]);
      double xPosition(det_prop.ConvertTicksToX(
        recobHit->PeakTime(), hitWireID.Plane, hitWireID.TPC, hitWireID.Cryostat));

      m_clusterHit2DMasterVec.emplace_back(0, 0., 0., xPosition, hitPeakTime, hitWireID, recobHit);

      recobHitTo2DHitMap[recobHit] = &m_clusterHit2DMasterVec.back();
    }

    // Now we can go through the space points and build our 3D hits
    for (auto& pointPair : spacePointHitVecMap) {
      const recob::SpacePoint* spacePoint = pointPair.first;
      const std::vector<const recob::Hit*>& recobHitVec = pointPair.second;

      if (recobHitVec.size() != 3) {
        std::cout << "************>>>>>> do not have 3 hits associated to space point! "
                  << recobHitVec.size() << " ***************" << std::endl;
        continue;
      }

      reco::ClusterHit2DVec hitVector(recobHitVec.size());

      for (const auto& recobHit : recobHitVec) {
        const reco::ClusterHit2D* hit2D = recobHitTo2DHitMap.at(recobHit);

        hitVector[hit2D->WireID().Plane] = hit2D;
      }

      // Set up to get average peak time, hitChiSquare, etc.
      unsigned int statusBits(0x7);
      float avePeakTime(0.);
      float weightSum(0.);

      // And get the wire IDs
      std::vector<geo::WireID> wireIDVec = {geo::WireID(), geo::WireID(), geo::WireID()};

      // First loop through the hits to get WireIDs and calculate the averages
      for (size_t planeIdx = 0; planeIdx < 3; planeIdx++) {
        const reco::ClusterHit2D* hit2D = hitVector[planeIdx];

        wireIDVec[planeIdx] = hit2D->WireID();

        if (hit2D->getStatusBits() & reco::ClusterHit2D::USEDINTRIPLET)
          hit2D->setStatusBit(reco::ClusterHit2D::SHAREDINTRIPLET);

        hit2D->setStatusBit(reco::ClusterHit2D::USEDINTRIPLET);

        float hitRMS = hit2D->getHit()->RMS();
        float weight = 1. / (hitRMS * hitRMS);
        float peakTime = hit2D->getTimeTicks();

        avePeakTime += peakTime * weight;
        weightSum += weight;
      }

      avePeakTime /= weightSum;

      // Armed with the average peak time, now get hitChiSquare and the sig vec
      float hitChiSquare(0.);
      float sigmaPeakTime(std::sqrt(1. / weightSum));
      std::vector<float> hitDelTSigVec;

      for (const auto& hit2D : hitVector) {
        float hitRMS = hit2D->getHit()->RMS();
        float combRMS = std::sqrt(hitRMS * hitRMS - sigmaPeakTime * sigmaPeakTime);
        float peakTime = hit2D->getTimeTicks();
        float deltaTime = peakTime - avePeakTime;
        float hitSig = deltaTime / combRMS;

        hitChiSquare += hitSig * hitSig;

        hitDelTSigVec.emplace_back(std::fabs(hitSig));
      }

      if (m_outputHistograms) m_chiSquare3DVec.push_back(hitChiSquare);

      // Need to determine the hit overlap ranges
      int lowMinIndex(std::numeric_limits<int>::max());
      int lowMaxIndex(std::numeric_limits<int>::min());
      int hiMinIndex(std::numeric_limits<int>::max());
      int hiMaxIndex(std::numeric_limits<int>::min());

      // This loop through hits to find min/max values for the common overlap region
      for (const auto& hit2D : hitVector) {
        int hitStart = hit2D->getHit()->PeakTime() - 2. * hit2D->getHit()->RMS() - 0.5;
        int hitStop = hit2D->getHit()->PeakTime() + 2. * hit2D->getHit()->RMS() + 0.5;

        lowMinIndex = std::min(hitStart, lowMinIndex);
        lowMaxIndex = std::max(hitStart, lowMaxIndex);
        hiMinIndex = std::min(hitStop + 1, hiMinIndex);
        hiMaxIndex = std::max(hitStop + 1, hiMaxIndex);
      }

      // Keep only "good" hits...
      if (hitChiSquare < m_maxHit3DChiSquare && hiMinIndex > lowMaxIndex) {
        // One more pass through hits to get charge
        std::vector<float> chargeVec;

        for (const auto& hit2D : hitVector)
          chargeVec.push_back(chargeIntegral(hit2D->getHit()->PeakTime(),
                                             hit2D->getHit()->PeakAmplitude(),
                                             hit2D->getHit()->RMS(),
                                             1.,
                                             lowMaxIndex,
                                             hiMinIndex));

        float totalCharge =
          std::accumulate(chargeVec.begin(), chargeVec.end(), 0.) / float(chargeVec.size());
        float overlapRange = float(hiMinIndex - lowMaxIndex);
        float overlapFraction = overlapRange / float(hiMaxIndex - lowMinIndex);

        // Set up to compute the charge asymmetry
        std::vector<float> smallestChargeDiffVec;
        std::vector<float> chargeAveVec;
        float smallestDiff(std::numeric_limits<float>::max());
        size_t chargeIndex(0);

        for (size_t idx = 0; idx < 3; idx++) {
          size_t leftIdx = (idx + 2) % 3;
          size_t rightIdx = (idx + 1) % 3;

          smallestChargeDiffVec.push_back(std::abs(chargeVec[leftIdx] - chargeVec[rightIdx]));
          chargeAveVec.push_back(float(0.5 * (chargeVec[leftIdx] + chargeVec[rightIdx])));

          if (smallestChargeDiffVec.back() < smallestDiff) {
            smallestDiff = smallestChargeDiffVec.back();
            chargeIndex = idx;
          }

          // Take opportunity to look at peak time diff
          if (m_outputHistograms) {
            float deltaPeakTime =
              hitVector[leftIdx]->getTimeTicks() - hitVector[rightIdx]->getTimeTicks();

            m_deltaTimeVec.push_back(deltaPeakTime);
          }
        }

        float chargeAsymmetry = (chargeAveVec[chargeIndex] - chargeVec[chargeIndex]) /
                                (chargeAveVec[chargeIndex] + chargeVec[chargeIndex]);

        // If this is true there has to be a negative charge that snuck in somehow
        if (chargeAsymmetry < -1. || chargeAsymmetry > 1.) {
          const geo::WireID& hitWireID = hitVector[chargeIndex]->WireID();

          std::cout << "============> Charge asymmetry out of range: " << chargeAsymmetry
                    << " <============" << std::endl;
          std::cout << "     hit C: " << hitWireID.Cryostat << ", TPC: " << hitWireID.TPC
                    << ", Plane: " << hitWireID.Plane << ", Wire: " << hitWireID.Wire << std::endl;
          std::cout << "     charge: " << chargeVec[0] << ", " << chargeVec[1] << ", "
                    << chargeVec[2] << std::endl;
          std::cout << "     index: " << chargeIndex << ", smallest diff: " << smallestDiff
                    << std::endl;
          continue;
        }

        // Usurping "deltaPeakTime" to be the maximum pull
        float deltaPeakTime = *std::max_element(hitDelTSigVec.begin(), hitDelTSigVec.end());

        if (m_outputHistograms) {
          m_smallChargeDiffVec.push_back(smallestDiff);
          m_smallIndexVec.push_back(chargeIndex);
          m_maxPullVec.push_back(deltaPeakTime);
          m_qualityMetricVec.push_back(hitChiSquare);
          m_spacePointChargeVec.push_back(totalCharge);
          m_overlapFractionVec.push_back(overlapFraction);
          m_overlapRangeVec.push_back(overlapRange);
          m_hitAsymmetryVec.push_back(chargeAsymmetry);
        }

        Eigen::Vector3f position(
          float(spacePoint->XYZ()[0]), float(spacePoint->XYZ()[1]), float(spacePoint->XYZ()[2]));

        // Create the 3D cluster hit
        hitPairList.emplace_back(0,
                                 statusBits,
                                 position,
                                 totalCharge,
                                 avePeakTime,
                                 deltaPeakTime,
                                 sigmaPeakTime,
                                 hitChiSquare,
                                 overlapFraction,
                                 chargeAsymmetry,
                                 0.,
                                 0.,
                                 hitVector,
                                 hitDelTSigVec,
                                 wireIDVec);
      }
    }

    // Now we give the new hits to the refinery
    // Note that one advantage of using this utility is that it handles the
    // Hit/Wire and Hit/RawDigit associations all behind the scenes for us
    hitRefiner.use_hits(std::move(newHitVecPtr));

    // Output the new hit collection to the event
    hitRefiner.put_into();

    // Handle tree output too
    m_tupleTree->Fill();

    clear();

    if (fEnableMonitoring) {
      theClockMakeHits.stop();

      fTimeVector[BUILDTHREEDHITS] = theClockMakeHits.accumulated_real_time();
    }

    mf::LogDebug("Cluster3D") << ">>>>> 3D hit building done, found " << hitPairList.size()
                              << " 3D Hits" << std::endl;

    return;
  }

  float
  SpacePointHit3DBuilder::chargeIntegral(float peakMean,
                                         float peakAmp,
                                         float peakSigma,
                                         float areaNorm,
                                         int low,
                                         int hi) const
  {
    float integral(0);

    for (int sigPos = low; sigPos < hi; sigPos++) {
      float arg = (float(sigPos) - peakMean + 0.5) / peakSigma;
      integral += peakAmp * std::exp(-0.5 * arg * arg);
    }

    return integral;
  }

  //------------------------------------------------------------------------------------------------------------------------------------------
  //------------------------------------------------------------------------------------------------------------------------------------------

  DEFINE_ART_CLASS_TOOL(SpacePointHit3DBuilder)
} // namespace lar_cluster3d