SolenoidalIntersector.h

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/

// SolenoidalIntersector.h, (c) ATLAS Detector software
 
#ifndef TRKEXSOLENOIDALINTERSECTOR_SOLENOIDALINTERSECTOR_H
#define TRKEXSOLENOIDALINTERSECTOR_SOLENOIDALINTERSECTOR_H
 
#include <cmath>
#include <mutex>
 
#include "AthenaBaseComps/AthAlgTool.h"
#include "CxxUtils/checker_macros.h"
#include "GaudiKernel/ContextSpecificPtr.h"
#include "GaudiKernel/ToolHandle.h"
#include "GeoPrimitives/GeoPrimitives.h"
#include "MagFieldConditions/AtlasFieldCacheCondObj.h"
#include "StoreGate/ReadCondHandle.h"
#include "StoreGate/ReadCondHandleKey.h"
#include "TrkExInterfaces/IIntersector.h"
#include "TrkExSolenoidalIntersector/SolenoidParametrization.h"
#include "TrkExUtils/TrackSurfaceIntersection.h"
 
namespace Trk {
 
class SolenoidalIntersector final: public extends<AthAlgTool, IIntersector> {
 
 public:
  struct Constants final: public TrackSurfaceIntersection::IIntersectionCache {
    Constants(const SolenoidParametrization& solpar,
              const TrackSurfaceIntersection& trackTrackSurfaceIntersection,
              const double qOverP);
    virtual std::unique_ptr<IIntersectionCache> clone() const override {
      return std::unique_ptr<IIntersectionCache>(new Constants(*this));
    }
    double m_sinTheta;
    double m_oneOverSinTheta;
    double m_cotTheta;
    double m_qOverPt;
    const SolenoidParametrization& m_solPar;
    Amg::Vector3D m_lastPosition;
    SolenoidParametrization::Parameters m_solParams;
  };
  SolenoidalIntersector(const std::string& type, const std::string& name,
                        const IInterface* parent);
  virtual ~SolenoidalIntersector() = default;
 
  virtual StatusCode initialize() override;
  virtual StatusCode finalize() override;

  virtual std::optional<TrackSurfaceIntersection> intersectSurface(
      const Surface& surface,
      const TrackSurfaceIntersection& trackTrackSurfaceIntersection,
      const double qOverP) const override;

  virtual std::optional<TrackSurfaceIntersection> approachPerigeeSurface(
      const PerigeeSurface& surface,
      const TrackSurfaceIntersection& trackTrackSurfaceIntersection,
      const double qOverP) const override;

  virtual std::optional<TrackSurfaceIntersection> approachStraightLineSurface(
      const StraightLineSurface& surface,
      const TrackSurfaceIntersection& trackTrackSurfaceIntersection,
      const double qOverP) const override;

  virtual std::optional<TrackSurfaceIntersection> intersectCylinderSurface(
      const CylinderSurface& surface,
      const TrackSurfaceIntersection& trackTrackSurfaceIntersection,
      const double qOverP) const override;

  virtual std::optional<TrackSurfaceIntersection> intersectDiscSurface(
      const DiscSurface& surface,
      const TrackSurfaceIntersection& trackTrackSurfaceIntersection,
      const double qOverP) const override;

  virtual std::optional<TrackSurfaceIntersection> intersectPlaneSurface(
      const PlaneSurface& surface,
      const TrackSurfaceIntersection& trackTrackSurfaceIntersection,
      const double qOverP) const override;

  virtual bool isValid(Amg::Vector3D startPosition,
                       Amg::Vector3D endPosition) const override;
 
 
 private:
  void throwMissingCondData() const;
  const SolenoidParametrization* getSolenoidParametrization() const {
    SG::ReadCondHandle<SolenoidParametrization> handle(
        m_solenoidParametrizationKey);
    if (!handle.isValid()) {
      throwMissingCondData();
    }
    return handle.cptr();
  }
 
  double circularArcLength(double, double, double, double, double, double,
                           double&, double&) const;
  double linearArcLength(const TrackSurfaceIntersection& isect,
                         const Constants& com, const double radius2,
                         const double endRadius) const;
  bool extrapolateToR(TrackSurfaceIntersection& isect, double& radius2,
                      Constants& com, const double endRadius) const;
 
  static bool extrapolateToZ(TrackSurfaceIntersection& isect, Constants& com,
                             const double endZ);
 
   std::optional<TrackSurfaceIntersection> intersection(
      TrackSurfaceIntersection&& isect, Constants& com,
      const Surface& surface) const;
 
  static std::optional<TrackSurfaceIntersection> newIntersection(
      const TrackSurfaceIntersection& oldIsect,
      const SolenoidParametrization& solpar, const double qOverP,
      Constants*& com);
 
  SG::ReadCondHandleKey<SolenoidParametrization> m_solenoidParametrizationKey{
      this, "SolenoidParameterizationKey", "SolenoidParametrization", ""};
  ToolHandle<IIntersector> m_rungeKuttaIntersector{this, "RungeKuttaIntersector",
    "Trk::RungeKuttaIntersector/RungeKuttaIntersector"};
 
  static constexpr double m_deltaPhiTolerance = 0.01; // upper limit for small angle approx
  DoubleProperty m_surfaceTolerance{this, "SurfaceTolerance",
    2.0 * Gaudi::Units::micrometer};
 
  // counters
  mutable std::atomic<unsigned long long> m_countExtrapolations = 0;
  mutable std::atomic<unsigned long long> m_countRKSwitches = 0;
};
 
// arc length to intersect of 2 circles: circular track and circle at (0,0) with
// radius endRadius
inline double SolenoidalIntersector::circularArcLength(
    double endRadius, double radiusOfCurvature, double xCentre, double yCentre,
    double cosPhi, double sinPhi, double& cosPhiIntersect,
    double& sinPhiIntersect) const {
  int trapped = 0;
  double radiusSquared = xCentre * xCentre + yCentre * yCentre;
  double term = 0.5 *
                (radiusSquared + radiusOfCurvature * radiusOfCurvature -
                 endRadius * endRadius) /
                (radiusSquared * radiusOfCurvature);
  if (std::abs(xCentre) < std::abs(yCentre)) {
    double dx2 = yCentre * yCentre * (1. / (radiusSquared * term * term) - 1.);
    if (dx2 < 0.) {
      trapped = 1;
    } else {
      if (yCentre * term > 0.) {
        sinPhiIntersect = term * (-xCentre + std::sqrt(dx2));
      } else {
        sinPhiIntersect = term * (-xCentre - std::sqrt(dx2));
      }
      cosPhiIntersect =
          (sinPhiIntersect * xCentre + radiusSquared * term) / yCentre;
    }
  } else {
    double dy2 = xCentre * xCentre * (1. / (radiusSquared * term * term) - 1.);
    if (dy2 < 0.) {
      trapped = 1;
    } else {
      if (xCentre * term > 0.) {
        cosPhiIntersect = term * (yCentre + std::sqrt(dy2));
      } else {
        cosPhiIntersect = term * (yCentre - std::sqrt(dy2));
      }
      sinPhiIntersect =
          (cosPhiIntersect * yCentre - radiusSquared * term) / xCentre;
    }
  }
  if (trapped == 0) {
    double deltaPhi;
    double sinDeltaPhi = sinPhiIntersect * cosPhi - cosPhiIntersect * sinPhi;
    if (std::abs(sinDeltaPhi) > 0.1) {
      deltaPhi = std::asin(sinDeltaPhi);
    } else {
      deltaPhi = sinDeltaPhi * (1. + 0.166667 * sinDeltaPhi * sinDeltaPhi);
    }
    return (radiusOfCurvature * deltaPhi);
  } else {
    cosPhiIntersect = cosPhi;
    sinPhiIntersect = sinPhi;
    return 0.;
  }
}
 
// arc length to intersect of a line to a circle of radius endRadius centred at
// (0,0) +ve (-ve) endRadius selects the solution on the same (opposite) side of
// (0,0)
inline double SolenoidalIntersector::linearArcLength(
    const TrackSurfaceIntersection& isect, const Constants& com,
    const double radius2, const double endRadius) const {
  const Amg::Vector3D& pos = isect.position();
  const Amg::Vector3D& dir = isect.direction();
 
  double arcLength =
      (-dir.x() * pos.x() - dir.y() * pos.y()) * com.m_oneOverSinTheta;
  double radiusSquared =
      endRadius * endRadius - radius2 + arcLength * arcLength;
  if (radiusSquared > 0.) {
    if (endRadius > 0.) {
      arcLength += std::sqrt(radiusSquared);
    } else {
      arcLength -= std::sqrt(radiusSquared);
    }
  }
  return arcLength;
}
 
inline std::optional<TrackSurfaceIntersection> SolenoidalIntersector::intersection(
    TrackSurfaceIntersection&& isect, Constants& com,
    const Surface& surface) const {
  // Improve the estimate of the intersection by calculating
  // the straight-line intersection.
  Intersection SLIntersect = surface.straightLineIntersection(
      isect.position(), isect.direction(), false, false);
  if (SLIntersect.valid) {
    // But first save our current position, so that we can
    // start from here on the next call.
    com.m_lastPosition = isect.position();
    isect.position() = SLIntersect.position;
    return std::move(isect);
  }
 
  return std::nullopt;
}
 
}  // namespace Trk
 
#endif  // TRKEXSOLENOIDALINTERSECTOR_SOLENOIDALINTERSECTOR_H