algorithms/tracking/DD4hepBField.h

0001 // This file is part of the Acts project.
0002 //
0003 // Copyright (C) 2016-2018 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 http://mozilla.org/MPL/2.0/.
0008
0009 #pragma once
0010
0011 #include <Acts/Definitions/Algebra.hpp>
0012 #include <Acts/MagneticField/MagneticFieldContext.hpp>
0013 #include <Acts/MagneticField/MagneticFieldProvider.hpp>
0014 #include <Acts/Utilities/Result.hpp>
0015 #include <DD4hep/Detector.h>
0016 #include <gsl/pointers>
0017 #include <memory>
0018 #include <utility>
0019 #include <variant>
0020
0021 namespace eicrecon::BField {
0022
0023 ///// The Context to be handed around
0024 //struct ScalableBFieldContext {
0025 //  double scalor = 1.;
0026 //};
0027
0028 /** Use the dd4hep magnetic field in acts.
0029    *
0030    * \ingroup magnets
0031    * \ingroup magsvc
0032    */
0033 class DD4hepBField final : public Acts::MagneticFieldProvider {
0034 public:
0035   gsl::not_null<const dd4hep::Detector*> m_det;
0036
0037 public:
0038   struct Cache {
0039     Cache(const Acts::MagneticFieldContext& /*mcfg*/) {}
0040   };
0041
0042   Acts::MagneticFieldProvider::Cache
0043   makeCache(const Acts::MagneticFieldContext& mctx) const override {
0044     return Acts::MagneticFieldProvider::Cache(std::in_place_type<Cache>, mctx);
0045   }
0046
0047   /** construct constant magnetic field from field vector.
0048     *
0049     * @param [in] DD4hep detector instance
0050     */
0051   explicit DD4hepBField(gsl::not_null<const dd4hep::Detector*> det) : m_det(det) {}
0052
0053   /**  retrieve magnetic field value.
0054      *
0055      *  @param [in] position global position
0056      *  @param [in] cache Cache object (is ignored)
0057      *  @return magnetic field vector
0058      *
0059      *  @note The @p position is ignored and only kept as argument to provide
0060      *        a consistent interface with other magnetic field services.
0061      */
0062   Acts::Result<Acts::Vector3> getField(const Acts::Vector3& position,
0063                                        Acts::MagneticFieldProvider::Cache& cache) const override;
0064
0065 #if Acts_VERSION_MAJOR < 39
0066   /** @brief retrieve magnetic field value & its gradient
0067      *
0068      * @param [in]  position   global position
0069      * @param [out] derivative gradient of magnetic field vector as (3x3)
0070      * matrix
0071      * @param [in] cache Cache object (is ignored)
0072      * @return magnetic field vector
0073      *
0074      * @note The @p position is ignored and only kept as argument to provide
0075      *       a consistent interface with other magnetic field services.
0076      * @note currently the derivative is not calculated
0077      * @todo return derivative
0078      */
0079   Acts::Result<Acts::Vector3>
0080   getFieldGradient(const Acts::Vector3& position, Acts::ActsMatrix<3, 3>& /*derivative*/,
0081                    Acts::MagneticFieldProvider::Cache& cache) const override;
0082 #endif
0083 };
0084
0085 using BFieldVariant = std::variant<std::shared_ptr<const DD4hepBField>>;
0086
0087 } // namespace eicrecon::BField