AreaSeededTrackingRegionsBuilder.cc

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#include "AreaSeededTrackingRegionsBuilder.h"

#include "FWCore/Utilities/interface/InputTag.h"
#include "DataFormats/Common/interface/Handle.h"
#include "DataFormats/Math/interface/PtEtaPhiMass.h"
#include "DataFormats/Math/interface/deltaPhi.h"
#include "RecoTracker/MeasurementDet/interface/MeasurementTrackerEvent.h"

#include <array>
#include <limits>

namespace {
  float perp2(const std::array<float, 2>& a) {
    return a[0]*a[0] + a[1]*a[1];
  }
}

AreaSeededTrackingRegionsBuilder::AreaSeededTrackingRegionsBuilder(const edm::ParameterSet& regPSet, edm::ConsumesCollector& iC) {
  m_extraPhi = regPSet.getParameter<double>("extraPhi");
  m_extraEta = regPSet.getParameter<double>("extraEta");

  // RectangularEtaPhiTrackingRegion parameters:
  m_ptMin            = regPSet.getParameter<double>("ptMin");
  m_originRadius     = regPSet.getParameter<double>("originRadius");
  m_precise          = regPSet.getParameter<bool>("precise");
  m_whereToUseMeasurementTracker = RectangularEtaPhiTrackingRegion::stringToUseMeasurementTracker(regPSet.getParameter<std::string>("whereToUseMeasurementTracker"));
  if(m_whereToUseMeasurementTracker != RectangularEtaPhiTrackingRegion::UseMeasurementTracker::kNever) {
    token_measurementTracker = iC.consumes<MeasurementTrackerEvent>(regPSet.getParameter<edm::InputTag>("measurementTrackerName"));
  }
  m_searchOpt = regPSet.getParameter<bool>("searchOpt");
}

void AreaSeededTrackingRegionsBuilder::fillDescriptions(edm::ParameterSetDescription& desc) {
  desc.add<double>("extraPhi", 0.);
  desc.add<double>("extraEta", 0.);

  desc.add<double>("ptMin", 0.9);
  desc.add<double>("originRadius", 0.2);
  desc.add<bool>("precise", true);

  desc.add<std::string>("whereToUseMeasurementTracker", "Never");
  desc.add<edm::InputTag>("measurementTrackerName", edm::InputTag(""));

  desc.add<bool>("searchOpt", false);
}

AreaSeededTrackingRegionsBuilder::Builder AreaSeededTrackingRegionsBuilder::beginEvent(const edm::Event& e) const {
  auto builder = Builder(this);

  if( !token_measurementTracker.isUninitialized() ) {
    edm::Handle<MeasurementTrackerEvent> hmte;
    e.getByToken(token_measurementTracker, hmte);
    builder.setMeasurementTracker(hmte.product());
  }

  return builder;
}


std::vector<std::unique_ptr<TrackingRegion> > AreaSeededTrackingRegionsBuilder::Builder::regions(const Origins& origins, const std::vector<Area>& areas) const {
  std::vector<std::unique_ptr<TrackingRegion> > result;

  // create tracking regions in directions of the points of interest
  int n_regions = 0;
  for(const auto& origin: origins) {
    result.push_back(region(origin, areas));
    ++n_regions;
  }
  LogDebug("AreaSeededTrackingRegionsBuilder") << "produced "<<n_regions<<" regions";

  return result;
}

std::unique_ptr<TrackingRegion> AreaSeededTrackingRegionsBuilder::Builder::region(const Origin& origin, const std::vector<Area>& areas) const {
  return regionImpl(origin, areas);
}
std::unique_ptr<TrackingRegion> AreaSeededTrackingRegionsBuilder::Builder::region(const Origin& origin, const edm::VecArray<Area, 2>& areas) const {
  return regionImpl(origin, areas);
}

template <typename T>
std::unique_ptr<TrackingRegion> AreaSeededTrackingRegionsBuilder::Builder::regionImpl(const Origin& origin, const T& areas) const {
  float minEta=std::numeric_limits<float>::max(), maxEta=std::numeric_limits<float>::lowest();
  float minPhi=std::numeric_limits<float>::max(), maxPhi=std::numeric_limits<float>::lowest();

  const auto& orig = origin.first;

  LogDebug("AreaSeededTrackingRegionsProducer") << "Origin x,y,z " << orig.x() << "," << orig.y() << "," << orig.z();

  auto vecFromOrigPlusRadius = [&](const std::array<float, 2>& vec) {
      const auto invlen = 1.f/std::sqrt(perp2(vec));
      const auto tmp = (1.f - m_conf->m_originRadius*invlen);
      return std::array<float, 2>{{vec[0]*tmp, vec[1]*tmp}};
  };
  auto tangentVec = [&](const std::array<float, 2>& vec, int sign) {
    const auto d = std::sqrt(perp2(vec));
    const auto r = m_conf->m_originRadius;
    const auto tmp = r/std::sqrt(d*d - r*r);
    // sign+ for counterclockwise, sign- for clockwise
    const auto orthvec = sign > 0 ? std::array<float, 2>{{-vec[1]*tmp,  vec[0]*tmp}}
                                  : std::array<float, 2>{{ vec[1]*tmp, -vec[0]*tmp}};
    return std::array<float, 2>{{vec[0]-orthvec[0], vec[1]-orthvec[1]}};
  };

  for(const auto& area: areas) {
    // straight line assumption is conservative, accounding for
    // low-pT bending would only tighten the eta-phi window
    LogTrace("AreaSeededTrackingRegionsBuilder") << " area x,y points "
                                                 << area.x_rmin_phimin() << "," << area.y_rmin_phimin() << " " // go around
                                                 << area.x_rmin_phimax() << "," << area.y_rmin_phimax() << " "
                                                 << area.x_rmax_phimax() << "," << area.y_rmax_phimax() << " "
                                                 << area.x_rmax_phimin() << "," << area.y_rmax_phimin() << " "
                                                 << "z " << area.zmin() << "," << area.zmax();

    // some common variables
    const float x_rmin_phimin = area.x_rmin_phimin()-orig.x();
    const float x_rmin_phimax = area.x_rmin_phimax()-orig.x();
    const float y_rmin_phimin = area.y_rmin_phimin()-orig.y();
    const float y_rmin_phimax = area.y_rmin_phimax()-orig.y();

    const std::array<float, 2> p_rmin_phimin = {{x_rmin_phimin, y_rmin_phimin}};
    const std::array<float, 2> p_rmin_phimax = {{x_rmin_phimax, y_rmin_phimax}};
    const std::array<float, 2> p_rmax_phimin = {{area.x_rmax_phimin() - orig.x(), area.y_rmax_phimin() - orig.y()}};
    const std::array<float, 2> p_rmax_phimax = {{area.x_rmax_phimax() - orig.x(), area.y_rmax_phimax() - orig.y()}};


    // eta
    {
      // find which of the two rmin points is closer to the origin
      //
      // closest point for p_rmin, farthest point for p_rmax
      const std::array<float, 2> p_rmin = perp2(p_rmin_phimin) < perp2(p_rmin_phimax) ? p_rmin_phimin : p_rmin_phimax;
      const std::array<float, 2> p_rmax = perp2(p_rmax_phimin) > perp2(p_rmax_phimax) ? p_rmax_phimin : p_rmax_phimax;

      // then calculate the xy vector from the point closest to p_rmin on
      // the (origin,originRadius) circle to the p_rmin
      // this will maximize the eta window
      const auto p_min = vecFromOrigPlusRadius(p_rmin);
      const auto p_max = vecFromOrigPlusRadius(p_rmax);

      // then we calculate the maximal eta window
      const auto etamin = std::min(etaFromXYZ(p_min[0], p_min[1], area.zmin() - (orig.z()+origin.second)),
                                   etaFromXYZ(p_max[0], p_max[1], area.zmin() - (orig.z()+origin.second)));
      const auto etamax = std::max(etaFromXYZ(p_min[0], p_min[1], area.zmax() - (orig.z()-origin.second)),
                                   etaFromXYZ(p_max[0], p_max[1], area.zmax() - (orig.z()-origin.second)));

      LogTrace("AreaSeededTrackingRegionBuilder") << "  eta min,max " << etamin << "," << etamax;

      minEta = std::min(minEta, etamin);
      maxEta = std::max(maxEta, etamax);
    }

    // phi
    {
      // For phi we construct the tangent lines of (origin,
      // originRadius) that go though each of the 4 points (in xy
      // plane) of the area. Easiest is to make a vector orthogonal to
      // origin->point vector which has a length of
      //
      // length = r*d/std::sqrt(d*d-r*r)
      //
      // where r is the originRadius and d is the distance from origin
      // to the point (to derive draw the situation and start with
      // definitions of sin/cos of one of the angles of the
      // right-angled triangle.

      // But we start with a "reference phi" so that we can easily
      // decide which phi is the largest/smallest without having too
      // much of headache with the wrapping. The reference is in
      // principle defined by the averages of y&x phimin/phimax at
      // rmin, but the '0.5f*' factor is omitted here to reduce
      // computations.
      const auto phi_ref = std::atan2(y_rmin_phimin + y_rmin_phimax,
                                      x_rmin_phimin + x_rmin_phimax);

      // for maximum phi we need the orthogonal vector to the left
      const auto tan_rmin_phimax = tangentVec(p_rmin_phimax, +1);
      const auto tan_rmax_phimax = tangentVec(p_rmax_phimax, +1);
      const auto phi_rmin_phimax = std::atan2(tan_rmin_phimax[1], tan_rmin_phimax[0]);
      const auto phi_rmax_phimax = std::atan2(tan_rmax_phimax[1], tan_rmax_phimax[0]);

      auto phimax = std::abs(reco::deltaPhi(phi_rmin_phimax, phi_ref)) > std::abs(reco::deltaPhi(phi_rmax_phimax, phi_ref)) ?
        phi_rmin_phimax : phi_rmax_phimax;

      LogTrace("AreaSeededTrackingRegionBuilder") << "   rmin_phimax vec " << p_rmin_phimax[0] << "," << p_rmin_phimax[1]
                                                  << " tangent " << tan_rmin_phimax[0] << "," << tan_rmin_phimax[1]
                                                  << " phi " << phi_rmin_phimax << "\n"
                                                  << "   rmax_phimax vec " << p_rmax_phimax[0] << "," << p_rmax_phimax[1]
                                                  << " tangent " << tan_rmax_phimax[0] << "," << tan_rmax_phimax[1]
                                                  << " phi " << phi_rmax_phimax << "\n"
                                                  << "   phimax " << phimax;



      // for minimum phi we need the orthogonal vector to the right
      const auto tan_rmin_phimin = tangentVec(p_rmin_phimin, -1);
      const auto tan_rmax_phimin = tangentVec(p_rmax_phimin, -1);
      const auto phi_rmin_phimin = std::atan2(tan_rmin_phimin[1], tan_rmin_phimin[0]);
      const auto phi_rmax_phimin = std::atan2(tan_rmax_phimin[1], tan_rmax_phimin[0]);

      auto phimin = std::abs(reco::deltaPhi(phi_rmin_phimin, phi_ref)) > std::abs(reco::deltaPhi(phi_rmax_phimin, phi_ref)) ?
        phi_rmin_phimin : phi_rmax_phimin;


      LogTrace("AreaSeededTrackingRegionBuilder") << "   rmin_phimin vec " << p_rmin_phimin[0] << "," << p_rmin_phimin[1]
                                                  << " tangent " << tan_rmin_phimin[0] << "," << tan_rmin_phimin[1]
                                                  << " phi " << phi_rmin_phimin << "\n"
                                                  << "   rmax_phimin vec " << p_rmax_phimin[0] << "," << p_rmax_phimin[1]
                                                  << " tangent " << tan_rmax_phimin[0] << "," << tan_rmax_phimin[1]
                                                  << " phi " << phi_rmax_phimin << "\n"
                                                  << "   phimin " << phimin;

      // wrapped around, need to decide which one to wrap
      if(phimax < phimin) {
        if(phimax < 0) phimax += 2*M_PI;
        else           phimin -= 2*M_PI;
      }

      LogTrace("AreaSeededTrackingRegionBuilder") << "  phi min,max " << phimin << "," << phimax;

      minPhi = std::min(minPhi, phimin);
      maxPhi = std::max(maxPhi, phimax);
    }

    LogTrace("AreaSeededTrackingRegionBuilder") << "  windows after this area  eta " << minEta << "," << maxEta
                                                << " phi " << minPhi << "," << maxPhi;
  }

  const auto meanEta = (minEta+maxEta)/2.f;
  const auto meanPhi = (minPhi+maxPhi)/2.f;
  const auto deltaEta = maxEta-meanEta + m_conf->m_extraEta;
  const auto deltaPhi = maxPhi-meanPhi + m_conf->m_extraPhi;

  const auto x = std::cos(meanPhi);
  const auto y = std::sin(meanPhi);
  const auto z = (x*x+y*y)/std::tan(2.f*std::atan(std::exp(-meanEta))); // simplify?

  LogTrace("AreaSeededTrackingRegionsBuilder") << "Direction x,y,z " << x << "," << y << "," << z
                                               << " eta,phi " << meanEta << "," << meanPhi
                                               << " window eta " << (meanEta-deltaEta) << "," << (meanEta+deltaEta)
                                               << " phi " << (meanPhi-deltaPhi) << "," << (meanPhi+deltaPhi);

  return std::make_unique<RectangularEtaPhiTrackingRegion>(
      GlobalVector(x,y,z),
      origin.first, // GlobalPoint
      m_conf->m_ptMin,
      m_conf->m_originRadius,
      origin.second,
      deltaEta,
      deltaPhi,
      m_conf->m_whereToUseMeasurementTracker,
      m_conf->m_precise,
      m_measurementTracker,
      m_conf->m_searchOpt
  );  
}