feat: add Python bindings for MagneticFieldMap (#1251)

* Adds missing Python bindings for `MagneticFieldMapXyz` and `MagneticFieldMapRz` to allow the field map to be read from a file.
* Add example use in `full_chain_itk.py`. Previously used a constant B-field.
* Also show different seeding options, and debug setting, commented out in `full_chain_itk.py`.

Examples/Detectors/MagneticField/src/FieldMapRootIo.cpp

@@ -6,7 +6,7 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-#include "FieldMapRootIo.hpp"
+#include "ActsExamples/MagneticField/FieldMapRootIo.hpp"
 
 #include "Acts/MagneticField/BFieldMapUtils.hpp"
 

Examples/Detectors/MagneticField/src/FieldMapTextIo.cpp

@@ -6,7 +6,7 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-#include "FieldMapTextIo.hpp"
+#include "ActsExamples/MagneticField/FieldMapTextIo.hpp"
 
 #include "Acts/MagneticField/BFieldMapUtils.hpp"
 

Examples/Detectors/MagneticField/src/MagneticFieldOptions.cpp

@@ -14,6 +14,8 @@
 #include "Acts/MagneticField/SolenoidBField.hpp"
 #include "Acts/Utilities/Logger.hpp"
 #include "ActsExamples/Framework/Sequencer.hpp"
+#include "ActsExamples/MagneticField/FieldMapRootIo.hpp"
+#include "ActsExamples/MagneticField/FieldMapTextIo.hpp"
 #include "ActsExamples/MagneticField/ScalableBFieldService.hpp"
 #include "ActsExamples/Utilities/Options.hpp"
 
@@ -24,9 +26,6 @@
 #include <boost/filesystem.hpp>
 #include <boost/program_options.hpp>
 
-#include "FieldMapRootIo.hpp"
-#include "FieldMapTextIo.hpp"
-
 void ActsExamples::Options::addMagneticFieldOptions(Description& desc) {
   using boost::program_options::bool_switch;
   using boost::program_options::value;

Examples/Python/src/MagneticField.cpp

@@ -14,9 +14,12 @@
 #include "Acts/MagneticField/NullBField.hpp"
 #include "Acts/MagneticField/SolenoidBField.hpp"
 #include "Acts/Plugins/Python/Utilities.hpp"
+#include "ActsExamples/MagneticField/FieldMapRootIo.hpp"
+#include "ActsExamples/MagneticField/FieldMapTextIo.hpp"
 
 #include <memory>
 
+#include <boost/filesystem.hpp>
 #include <pybind11/pybind11.h>
 
 namespace py = pybind11;
@@ -43,12 +46,12 @@ void addMagneticField(Context& ctx) {
       .def(py::init<Acts::Vector3>());
 
   py::class_<ActsExamples::detail::InterpolatedMagneticField2,
-             Acts::InterpolatedMagneticField,
+             Acts::InterpolatedMagneticField, Acts::MagneticFieldProvider,
              std::shared_ptr<ActsExamples::detail::InterpolatedMagneticField2>>(
       mex, "InterpolatedMagneticField2");
 
   py::class_<ActsExamples::detail::InterpolatedMagneticField3,
-             Acts::InterpolatedMagneticField,
+             Acts::InterpolatedMagneticField, Acts::MagneticFieldProvider,
              std::shared_ptr<ActsExamples::detail::InterpolatedMagneticField3>>(
       mex, "InterpolatedMagneticField3");
 
@@ -78,6 +81,71 @@ void addMagneticField(Context& ctx) {
         .def_readwrite("nCoils", &Config::nCoils)
         .def_readwrite("bMagCenter", &Config::bMagCenter);
   }
+
+  mex.def(
+      "MagneticFieldMapXyz",
+      [](std::string filename, std::string tree, double lengthUnit,
+         double BFieldUnit, bool firstOctant) {
+        const boost::filesystem::path file = filename;
+
+        auto mapBins = [](std::array<size_t, 3> bins,
+                          std::array<size_t, 3> sizes) {
+          return (bins[0] * (sizes[1] * sizes[2]) + bins[1] * sizes[2] +
+                  bins[2]);
+        };
+
+        if (file.extension() == ".root") {
+          auto map = ActsExamples::makeMagneticFieldMapXyzFromRoot(
+              std::move(mapBins), file.native(), tree, lengthUnit, BFieldUnit,
+              firstOctant);
+          return std::make_shared<
+              ActsExamples::detail::InterpolatedMagneticField3>(std::move(map));
+        } else if (file.extension() == ".txt") {
+          auto map = ActsExamples::makeMagneticFieldMapXyzFromText(
+              std::move(mapBins), file.native(), lengthUnit, BFieldUnit,
+              firstOctant);
+          return std::make_shared<
+              ActsExamples::detail::InterpolatedMagneticField3>(std::move(map));
+        } else {
+          throw std::runtime_error("Unsupported magnetic field map file type");
+        }
+      },
+      py::arg("file"), py::arg("tree") = "bField",
+      py::arg("lengthUnit") = Acts::UnitConstants::mm,
+      py::arg("BFieldUnit") = Acts::UnitConstants::T,
+      py::arg("firstOctant") = false);
+
+  mex.def(
+      "MagneticFieldMapRz",
+      [](std::string filename, std::string tree, double lengthUnit,
+         double BFieldUnit, bool firstQuadrant) {
+        const boost::filesystem::path file = filename;
+
+        auto mapBins = [](std::array<size_t, 2> bins,
+                          std::array<size_t, 2> sizes) {
+          return (bins[1] * sizes[0] + bins[0]);
+        };
+
+        if (file.extension() == ".root") {
+          auto map = ActsExamples::makeMagneticFieldMapRzFromRoot(
+              std::move(mapBins), file.native(), tree, lengthUnit, BFieldUnit,
+              firstQuadrant);
+          return std::make_shared<
+              ActsExamples::detail::InterpolatedMagneticField2>(std::move(map));
+        } else if (file.extension() == ".txt") {
+          auto map = ActsExamples::makeMagneticFieldMapRzFromText(
+              std::move(mapBins), file.native(), lengthUnit, BFieldUnit,
+              firstQuadrant);
+          return std::make_shared<
+              ActsExamples::detail::InterpolatedMagneticField2>(std::move(map));
+        } else {
+          throw std::runtime_error("Unsupported magnetic field map file type");
+        }
+      },
+      py::arg("file"), py::arg("tree") = "bField",
+      py::arg("lengthUnit") = Acts::UnitConstants::mm,
+      py::arg("BFieldUnit") = Acts::UnitConstants::T,
+      py::arg("firstQuadrant") = false);
 }
 
 }  // namespace Acts::Python

Examples/Scripts/Python/full_chain_itk.py

@@ -7,7 +7,7 @@
 
 # acts.examples.dump_args_calls(locals())
 detector, trackingGeometry, decorators = itk.buildITkGeometry(geo_dir)
-field = acts.ConstantBField(acts.Vector3(0.0, 0.0, 2.0 * u.T))
+field = acts.examples.MagneticFieldMapXyz(str(geo_dir / "bfield/ATLAS-BField-xyz.root"))
 rnd = acts.examples.RandomNumbers(seed=42)
 
 from particle_gun import addParticleGun, MomentumConfig, EtaConfig, ParticleConfig