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