Field.cc

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#include "MagneticField/Engine/interface/MagneticField.h"
#include "SimG4Core/MagneticField/interface/Field.h"

#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "G4Mag_UsualEqRhs.hh"

#include "CLHEP/Units/GlobalSystemOfUnits.h"

using namespace sim;

Field::Field(const MagneticField *f, double d) : G4MagneticField(), theCMSMagneticField(f), theDelta(d) {
  for (int i = 0; i < 3; ++i) {
    oldx[i] = 1.0e12;
    oldb[i] = 0.0;
  }
}

Field::~Field() {}

void Field::GetFieldValue(const G4double xyz[4], G4double bfield[3]) const {
  if (std::abs(oldx[0] - xyz[0]) > theDelta || std::abs(oldx[1] - xyz[1]) > theDelta ||
      std::abs(oldx[2] - xyz[2]) > theDelta) {
    static const float lunit = (float)(1.0 / CLHEP::cm);
    GlobalPoint ggg((float)(xyz[0]) * lunit, (float)(xyz[1]) * lunit, (float)(xyz[2]) * lunit);
    GlobalVector v = theCMSMagneticField->inTesla(ggg);

    static const float btesla = (float)CLHEP::tesla;
    oldb[0] = (G4double)(v.x() * btesla);
    oldb[1] = (G4double)(v.y() * btesla);
    oldb[2] = (G4double)(v.z() * btesla);
    oldx[0] = xyz[0];
    oldx[1] = xyz[1];
    oldx[2] = xyz[2];
  }

  bfield[0] = oldb[0];
  bfield[1] = oldb[1];
  bfield[2] = oldb[2];
}