feat: Add JSON detector element

Examples/Io/Json/include/ActsExamples/Io/Json/JsonSurfacesReader.hpp

@@ -9,6 +9,7 @@
 #pragma once
 
 #include "Acts/Geometry/GeometryHierarchyMap.hpp"
+#include "Acts/Plugins/Json/JsonDetectorElement.hpp"
 
 #include <memory>
 #include <string>
@@ -43,4 +44,13 @@ Acts::GeometryHierarchyMap<std::shared_ptr<Acts::Surface>> readHierarchyMap(
 /// @return  a vector of surfaces
 std::vector<std::shared_ptr<Acts::Surface>> readVector(const Options& options);
 
+/// @brief Read the surfaces from the input file and create
+/// detector elements
+///
+/// @param inputFile is the input file to read from
+///
+/// @return  a vector of surfaces
+std::vector<std::shared_ptr<Acts::JsonDetectorElement>> readDetectorElements(
+    const Options& options, double thickness);
+
 }  // namespace ActsExamples::JsonSurfacesReader

Examples/Io/Json/src/JsonSurfacesReader.cpp

@@ -73,4 +73,27 @@ std::vector<std::shared_ptr<Acts::Surface>> JsonSurfacesReader::readVector(
   return surfaces;
 }
 
+std::vector<std::shared_ptr<Acts::JsonDetectorElement>>
+JsonSurfacesReader::readDetectorElements(const Options& options,
+                                         double thickness = 0.0) {
+  nlohmann::json j;
+  {
+    std::ifstream in(options.inputFile);
+    in >> j;
+  }
+
+  // Walk down the path to the surface entries
+  nlohmann::json jSurfaces = j;
+  for (const auto& jep : options.jsonEntryPath) {
+    jSurfaces = jSurfaces[jep];
+  }
+
+  std::vector<std::shared_ptr<Acts::JsonDetectorElement>> elements;
+  for (const auto& jSurface : jSurfaces) {
+    elements.emplace_back(
+        std::make_shared<Acts::JsonDetectorElement>(jSurface, thickness));
+  }
+  return elements;
+}
+
 }  // namespace ActsExamples

Examples/Python/src/Json.cpp

@@ -168,6 +168,16 @@ void addJson(Context& ctx) {
 
     mex.def("readSurfaceVectorFromJson",
             ActsExamples::JsonSurfacesReader::readVector);
+
+    py::class_<Acts::JsonDetectorElement, Acts::DetectorElementBase,
+               std::shared_ptr<Acts::JsonDetectorElement>>(
+        mex, "JsonDetectorElement")
+        .def("surface", [](Acts::JsonDetectorElement& self) {
+          return self.surface().getSharedPtr();
+        });
+
+    mex.def("readDetectorElementsFromJson",
+            ActsExamples::JsonSurfacesReader::readDetectorElements);
   }
 
   {

Plugins/Json/CMakeLists.txt

@@ -22,6 +22,7 @@ add_library(
     src/VolumeJsonConverter.cpp
     src/AmbiguityConfigJsonConverter.cpp
     src/DetrayJsonHelper.cpp
+    src/JsonDetectorElement.cpp
 )
 target_include_directories(
     ActsPluginJson

Plugins/Json/include/Acts/Plugins/Json/JsonDetectorElement.hpp

@@ -0,0 +1,32 @@
+// This file is part of the ACTS project.
+//
+// Copyright (C) 2016 CERN for the benefit of the ACTS project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+#pragma once
+
+#include "Acts/Geometry/DetectorElementBase.hpp"
+
+#include <nlohmann/json.hpp>
+
+namespace Acts {
+
+class JsonDetectorElement : public DetectorElementBase {
+  std::shared_ptr<Surface> m_surface;
+  Transform3 m_transform{};
+  double m_thickness{};
+
+ public:
+  JsonDetectorElement(const nlohmann::json &surfaceJson, double thickness);
+
+  Surface &surface() override;
+  const Surface &surface() const override;
+
+  double thickness() const override;
+
+  const Transform3 &transform(const GeometryContext &gctx) const override;
+};
+
+}  // namespace Acts

Plugins/Json/src/JsonDetectorElement.cpp

@@ -0,0 +1,40 @@
+// This file is part of the ACTS project.
+//
+// Copyright (C) 2016 CERN for the benefit of the ACTS project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#include "Acts/Plugins/Json/JsonDetectorElement.hpp"
+
+#include "Acts/Plugins/Json/SurfaceJsonConverter.hpp"
+
+namespace Acts {
+
+JsonDetectorElement::JsonDetectorElement(const nlohmann::json &jSurface,
+                                         double thickness)
+    : m_thickness(thickness) {
+  m_surface = Acts::SurfaceJsonConverter::fromJson(jSurface);
+  m_transform = m_surface->transform({});
+  m_surface->assignDetectorElement(*this);
+}
+
+const Surface &JsonDetectorElement::surface() const {
+  return *m_surface;
+}
+
+Surface &JsonDetectorElement::surface() {
+  return *m_surface;
+}
+
+const Transform3 &JsonDetectorElement::transform(
+    const GeometryContext &) const {
+  return m_transform;
+}
+
+double JsonDetectorElement::thickness() const {
+  return m_thickness;
+}
+
+}  // namespace Acts