Geant4/src/MagneticFieldWrapper.cpp

0001 // This file is part of the ACTS project.
0002 //
0003 // Copyright (C) 2016 CERN for the benefit of the ACTS project
0004 //
0005 // This Source Code Form is subject to the terms of the Mozilla Public
0006 // License, v. 2.0. If a copy of the MPL was not distributed with this
0007 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
0008
0009 #include "ActsExamples/Geant4/MagneticFieldWrapper.hpp"
0010
0011 #include "Acts/Definitions/Algebra.hpp"
0012 #include "Acts/Definitions/Units.hpp"
0013 #include "Acts/MagneticField/MagneticFieldContext.hpp"
0014 #include "Acts/MagneticField/MagneticFieldProvider.hpp"
0015
0016 #include <utility>
0017
0018 #include <G4SystemOfUnits.hh>
0019 #include <G4UnitsTable.hh>
0020
0021 namespace ActsExamples::Geant4 {
0022
0023 MagneticFieldWrapper::MagneticFieldWrapper(
0024     const Config& cfg, std::unique_ptr<const Acts::Logger> logger)
0025     : G4MagneticField(), m_cfg(cfg), m_logger(std::move(logger)) {}
0026
0027 void MagneticFieldWrapper::GetFieldValue(const G4double Point[4],
0028                                          G4double* Bfield) const {
0029   constexpr double convertLength = CLHEP::mm / Acts::UnitConstants::mm;
0030   constexpr double convertField = CLHEP::tesla / Acts::UnitConstants::T;
0031
0032   auto bCache = m_cfg.magneticField->makeCache(Acts::MagneticFieldContext());
0033
0034   auto fieldRes = m_cfg.magneticField->getField(
0035       {convertLength * Point[0], convertLength * Point[1],
0036        convertLength * Point[2]},
0037       bCache);
0038   if (!fieldRes.ok()) {
0039     ACTS_ERROR("Field lookup error: " << fieldRes.error());
0040     return;
0041   }
0042   // Get the field now
0043   const Acts::Vector3& field = *fieldRes;
0044
0045   Bfield[0] = convertField * field[0];
0046   Bfield[1] = convertField * field[1];
0047   Bfield[2] = convertField * field[2];
0048 }
0049
0050 }  // namespace ActsExamples::Geant4