StraightLineBarrelCylinderCrossing.cc

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#include "TrackingTools/GeomPropagators/interface/StraightLineBarrelCylinderCrossing.h"
#include "DataFormats/GeometrySurface/interface/Cylinder.h"
#include "TrackingTools/GeomPropagators/src/RealQuadEquation.h"

#include <cmath>

StraightLineBarrelCylinderCrossing::StraightLineBarrelCylinderCrossing(const GlobalPoint& startingPos,
                                                                       const GlobalVector& startingDir,
                                                                       const PropagationDirection propDir)
    : theX0(startingPos), theP0(startingDir.unit()), thePropDir(propDir) {}

std::pair<bool, double> StraightLineBarrelCylinderCrossing::pathLength(const Cylinder& cylinder) const {
  //
  // radius of cylinder and transversal position relative to axis
  //
  double R(cylinder.radius());
  GlobalPoint axis(cylinder.toGlobal(Cylinder::LocalPoint(0., 0.)));
  PositionType2D xt2d(theX0.x() - axis.x(), theX0.y() - axis.y());
  //
  // transverse direction
  //
  DirectionType2D pt2d(theP0.x(), theP0.y());
  //
  // solution of quadratic equation for s - assume |theP0|=1
  //
  RealQuadEquation eq(pt2d.mag2(), 2. * xt2d.dot(pt2d), xt2d.mag2() - R * R);
  if (!eq.hasSolution)
    return std::pair<bool, double>(false, 0.);
  //
  // choice of solution and verification of direction
  //
  return chooseSolution(eq.first, eq.second);
}

std::pair<bool, double> StraightLineBarrelCylinderCrossing::chooseSolution(const double s1, const double s2) const {
  //
  // follows the logic implemented in HelixBarrelCylinderCrossing
  //
  if (thePropDir == anyDirection) {
    return std::pair<bool, double>(true, (fabs(s1) < fabs(s2) ? s1 : s2));
  } else {
    int propSign = thePropDir == alongMomentum ? 1 : -1;
    if (s1 * s2 < 0) {
      // if different signs return the positive one
      return std::pair<bool, double>(true, ((s1 * propSign > 0) ? s1 : s2));
    } else if (s1 * propSign > 0) {
      // if both positive, return the shortest
      return std::pair<bool, double>(true, (fabs(s1) < fabs(s2) ? s1 : s2));
    }
  }
  return std::pair<bool, double>(false, 0.);
}