algorithms/fardetectors/FarDetectorLinearTracking.cc

0001 // SPDX-License-Identifier: LGPL-3.0-or-later
0002 // Copyright (C) 2023 - 2025, Simon Gardner
0003
0004 #include <DD4hep/VolumeManager.h>
0005 #include <Evaluator/DD4hepUnits.h>
0006 #include <Math/GenVector/Cartesian3D.h>
0007 #include <Math/GenVector/DisplacementVector3D.h>
0008 #include <algorithms/geo.h>
0009 #include <edm4eic/Cov6f.h>
0010 #include <edm4eic/MCRecoTrackParticleAssociationCollection.h>
0011 #include <edm4eic/MCRecoTrackerHitAssociationCollection.h>
0012 #include <edm4eic/MCRecoTrackerHitLinkCollection.h>
0013 #include <edm4eic/Measurement2DCollection.h>
0014 #include <edm4eic/RawTrackerHit.h>
0015 #include <edm4eic/TrackCollection.h>
0016 #include <edm4eic/TrackerHit.h>
0017 #include <edm4hep/MCParticle.h>
0018 #include <edm4hep/SimTrackerHit.h>
0019 #include <edm4hep/Vector2f.h>
0020 #include <edm4hep/Vector3d.h>
0021 #include <edm4hep/Vector3f.h>
0022 #include <edm4hep/utils/vector_utils.h>
0023 #include <podio/LinkNavigator.h>
0024 #include <podio/RelationRange.h>
0025 #include <podio/detail/Link.h>
0026 #include <Eigen/Geometry>
0027 #include <Eigen/Householder>
0028 #include <Eigen/Jacobi>
0029 #include <Eigen/SVD>
0030 #include <algorithm>
0031 #include <cmath>
0032 #include <cstddef>
0033 #include <cstdint>
0034 #include <memory>
0035 #include <new>
0036 #include <tuple>
0037 #include <unordered_map>
0038 #include <utility>
0039
0040 #include "FarDetectorLinearTracking.h"
0041 #include "algorithms/fardetectors/FarDetectorLinearTrackingConfig.h"
0042
0043 namespace eicrecon {
0044
0045 void FarDetectorLinearTracking::init() {
0046
0047   // For changing how strongly each layer hit is in contributing to the fit
0048   m_layerWeights = Eigen::VectorXd::Constant(m_cfg.n_layer, 1);
0049
0050   for (std::size_t i = 0; i < std::min(m_cfg.layer_weights.size(), m_cfg.n_layer); i++) {
0051     m_layerWeights(i) = m_cfg.layer_weights[i];
0052   }
0053
0054   // For checking the direction of the track from theta and phi angles
0055   m_optimumDirection = Eigen::Vector3d::UnitZ();
0056   m_optimumDirection =
0057       Eigen::AngleAxisd(m_cfg.optimum_theta, Eigen::Vector3d::UnitY()) * m_optimumDirection;
0058   m_optimumDirection =
0059       Eigen::AngleAxisd(m_cfg.optimum_phi, Eigen::Vector3d::UnitZ()) * m_optimumDirection;
0060
0061   m_cellid_converter = algorithms::GeoSvc::instance().cellIDPositionConverter();
0062 }
0063
0064 void FarDetectorLinearTracking::process(const FarDetectorLinearTracking::Input& input,
0065                                         const FarDetectorLinearTracking::Output& output) const {
0066
0067   const auto [inputhits, hitLinks, assocHits]  = input;
0068   auto [outputTracks, trackLinks, assocTracks] = output;
0069
0070   // Check the number of input collections is correct
0071   std::size_t nCollections = inputhits.size();
0072   if (nCollections != m_cfg.n_layer) {
0073     error("Wrong number of input collections passed to algorithm");
0074     return;
0075   }
0076
0077   // Check if truth associations are possible
0078   const bool do_assoc = hitLinks != nullptr && !hitLinks->empty();
0079   if (!do_assoc) {
0080     debug("Provided MCRecoTrackerHitLink collection is empty. No truth associations "
0081           "will be performed.");
0082   }
0083   // Build fast lookup once per event using podio::LinkNavigator
0084   std::optional<podio::LinkNavigator<edm4eic::MCRecoTrackerHitLinkCollection>> link_nav;
0085   if (do_assoc) {
0086     link_nav.emplace(*hitLinks);
0087   }
0088
0089   std::vector<std::vector<Eigen::Vector3d>> convertedHits;
0090   std::vector<std::vector<edm4hep::MCParticle>> assocParts;
0091   convertedHits.reserve(m_cfg.n_layer);
0092   assocParts.reserve(m_cfg.n_layer);
0093
0094   // Check there aren't too many hits in any layer to handle
0095   // Temporary limit of number of hits per layer before Kalman filtering/GNN implemented
0096   // TODO - Implement more sensible solution
0097   for (const auto& layerHits : inputhits) {
0098     if ((*layerHits).size() > m_cfg.layer_hits_max) {
0099       info("Too many hits in layer");
0100       return;
0101     }
0102     if ((*layerHits).empty()) {
0103       trace("No hits in layer");
0104       return;
0105     }
0106     ConvertClusters(*layerHits, *link_nav, *assocHits, convertedHits, assocParts);
0107   }
0108
0109   // Create a matrix to store the hit positions
0110   Eigen::MatrixXd hitMatrix(3, m_cfg.n_layer);
0111
0112   // Create vector to store indexes of hits in the track
0113   std::vector<std::size_t> layerHitIndex(m_cfg.n_layer, 0);
0114
0115   int layer = 0;
0116
0117   // Iterate over all combinations of measurements in the layers without recursion
0118   while (true) {
0119     hitMatrix.col(layer) << convertedHits[layer][layerHitIndex[layer]];
0120
0121     bool isValid = true;
0122     // Check the last two hits are within a certain angle of the optimum direction
0123     if (layer > 0 && m_cfg.restrict_direction) {
0124       isValid = checkHitPair(hitMatrix.col(layer - 1), hitMatrix.col(layer));
0125     }
0126
0127     // If valid hit combination, move to the next layer or check the combination
0128     if (isValid) {
0129       if (layer == static_cast<long>(m_cfg.n_layer) - 1) {
0130         // Check the combination, if chi2 limit is passed, add the track to the output
0131         checkHitCombination(&hitMatrix, outputTracks, trackLinks, assocTracks, inputhits,
0132                             assocParts, layerHitIndex);
0133       } else {
0134         layer++;
0135         continue;
0136       }
0137     }
0138
0139     // Iterate current layer
0140     layerHitIndex[layer]++;
0141
0142     bool doBreak = false;
0143     // Set up next combination to check
0144     while (layerHitIndex[layer] >= convertedHits[layer].size()) {
0145       layerHitIndex[layer] = 0;
0146       if (layer == 0) {
0147         doBreak = true;
0148         break;
0149       }
0150       layer--;
0151       // Iterate previous layer
0152       layerHitIndex[layer]++;
0153     }
0154     if (doBreak) {
0155       break;
0156     }
0157   }
0158 }
0159
0160 void FarDetectorLinearTracking::checkHitCombination(
0161     Eigen::MatrixXd* hitMatrix, edm4eic::TrackCollection* outputTracks,
0162     edm4eic::MCRecoTrackParticleLinkCollection* trackLinks,
0163     edm4eic::MCRecoTrackParticleAssociationCollection* assocTracks,
0164     const std::vector<gsl::not_null<const edm4eic::Measurement2DCollection*>>& inputHits,
0165     const std::vector<std::vector<edm4hep::MCParticle>>& assocParts,
0166     const std::vector<std::size_t>& layerHitIndex) const {
0167
0168   Eigen::Vector3d weightedAnchor = (*hitMatrix) * m_layerWeights / (m_layerWeights.sum());
0169
0170   auto localMatrix = (*hitMatrix).colwise() - weightedAnchor;
0171
0172   Eigen::BDCSVD<Eigen::MatrixXd> svd(localMatrix.transpose(),
0173                                      Eigen::ComputeThinU | Eigen::ComputeThinV);
0174
0175   auto V = svd.matrixV();
0176
0177   // Rotate into principle components and calculate chi2/ndf
0178   auto rotatedMatrix = localMatrix.transpose() * V;
0179   auto residuals     = rotatedMatrix.rightCols(2);
0180   double chi2        = (residuals.array() * residuals.array()).sum() / (2 * m_cfg.n_layer);
0181
0182   if (chi2 > m_cfg.chi2_max) {
0183     return;
0184   }
0185
0186   edm4hep::Vector3d outPos = weightedAnchor.data();
0187   edm4hep::Vector3d outVec = V.col(0).data();
0188
0189   // Make sure fit was pointing in the right direction
0190   if (outVec.z > 0) {
0191     outVec = outVec * -1;
0192   }
0193
0194   int32_t type{0};                                          // Type of track
0195   edm4hep::Vector3f position(outPos.x, outPos.y, outPos.z); // Position of the trajectory point [mm]
0196   edm4hep::Vector3f momentum(outVec.x, outVec.y, outVec.z); // 3-momentum at the point [GeV]
0197   edm4eic::Cov6f positionMomentumCovariance;                // Error on the position
0198   float time{0};                                            // Time at this point [ns]
0199   float timeError{0};                                       // Error on the time at this point
0200   float charge{-1};                                         // Charge of the particle
0201   int32_t ndf{static_cast<int32_t>(m_cfg.n_layer) - 1};     // Number of degrees of freedom
0202   int32_t pdg{11};                                          // PDG code of the particle
0203
0204   // Create the track
0205   auto track = (*outputTracks)
0206                    .create(type, position, momentum, positionMomentumCovariance, time, timeError,
0207                            charge, chi2, ndf, pdg);
0208
0209   // Add Measurement2D relations and count occurrence of particles contributing to the track
0210   std::unordered_map<edm4hep::MCParticle, int> particleCount;
0211   for (std::size_t layer = 0; layer < layerHitIndex.size(); layer++) {
0212     track.addToMeasurements((*inputHits[layer])[layerHitIndex[layer]]);
0213     const auto& assocParticle = assocParts[layer][layerHitIndex[layer]];
0214     particleCount[assocParticle]++;
0215   }
0216
0217   // Create track associations for each particle
0218   for (const auto& [particle, count] : particleCount) {
0219     auto trackLink = trackLinks->create();
0220     trackLink.setFrom(track);
0221     trackLink.setTo(particle);
0222     trackLink.setWeight(count / static_cast<double>(m_cfg.n_layer));
0223     auto trackAssoc = assocTracks->create();
0224     trackAssoc.setRec(track);
0225     trackAssoc.setSim(particle);
0226     trackAssoc.setWeight(count / static_cast<double>(m_cfg.n_layer));
0227   }
0228 }
0229
0230 // Check if a pair of hits lies close to the optimum direction
0231 bool FarDetectorLinearTracking::checkHitPair(const Eigen::Vector3d& hit1,
0232                                              const Eigen::Vector3d& hit2) const {
0233
0234   Eigen::Vector3d hitDiff = hit2 - hit1;
0235   hitDiff.normalize();
0236
0237   double angle = std::acos(hitDiff.dot(m_optimumDirection));
0238
0239   debug("Vector: x={}, y={}, z={}", hitDiff.x(), hitDiff.y(), hitDiff.z());
0240   debug("Optimum: x={}, y={}, z={}", m_optimumDirection.x(), m_optimumDirection.y(),
0241         m_optimumDirection.z());
0242   debug("Angle: {}, Tolerance {}", angle, m_cfg.step_angle_tolerance);
0243
0244   return angle <= m_cfg.step_angle_tolerance;
0245 }
0246
0247 // Convert measurements into global coordinates
0248 void FarDetectorLinearTracking::ConvertClusters(
0249     const edm4eic::Measurement2DCollection& clusters,
0250     const podio::LinkNavigator<edm4eic::MCRecoTrackerHitLinkCollection>& link_nav,
0251     [[maybe_unused]] const edm4eic::MCRecoTrackerHitAssociationCollection& assoc_hits,
0252     std::vector<std::vector<Eigen::Vector3d>>& pointPositions,
0253     std::vector<std::vector<edm4hep::MCParticle>>& assoc_parts) const {
0254
0255   // Get context of first hit
0256   const dd4hep::VolumeManagerContext* context =
0257       m_cellid_converter->findContext(clusters[0].getSurface());
0258
0259   std::vector<Eigen::Vector3d> layerPositions;
0260   std::vector<edm4hep::MCParticle> assocParticles;
0261
0262   for (auto cluster : clusters) {
0263
0264     auto globalPos = context->localToWorld({cluster.getLoc()[0], cluster.getLoc()[1], 0});
0265     layerPositions.emplace_back(globalPos.x() / dd4hep::mm, globalPos.y() / dd4hep::mm,
0266                                 globalPos.z() / dd4hep::mm);
0267
0268     // Determine the MCParticle associated with this measurement based on the weights
0269     // Get hit in measurement with max weight
0270     float maxWeight      = 0;
0271     std::size_t maxIndex = cluster.getWeights().size();
0272     for (std::size_t i = 0; i < cluster.getWeights().size(); ++i) {
0273       if (cluster.getWeights()[i] > maxWeight) {
0274         maxWeight = cluster.getWeights()[i];
0275         maxIndex  = i;
0276       }
0277     }
0278     if (maxIndex == cluster.getWeights().size()) {
0279       // no maximum found (e.g. all weights zero, cluster size zero)
0280       continue;
0281     }
0282     auto maxHit = cluster.getHits()[maxIndex];
0283     // Get associated raw hit
0284     auto rawHit = maxHit.getRawHit();
0285
0286     const auto sim_hits = link_nav.getLinked(rawHit);
0287     if (!sim_hits.empty()) {
0288       auto particle = sim_hits[0].o.getParticle();
0289       assocParticles.push_back(particle);
0290     }
0291   }
0292
0293   pointPositions.push_back(layerPositions);
0294   assoc_parts.push_back(assocParticles);
0295 }
0296
0297 } // namespace eicrecon