add environment example

examples/CMakeLists.txt

@@ -64,3 +64,5 @@ CORSIKA_REGISTER_EXAMPLE (corsika RUN_OPTIONS --energy=100 --zenith=10 --nevent=
 add_executable (mars mars.cpp)
 target_link_libraries (mars CORSIKA8::CORSIKA8)
 
+add_executable (environment environment.cpp)
+target_link_libraries (environment CORSIKA8::CORSIKA8)

examples/environment_example.cpp

+#include <corsika/media/Environment.hpp>
+#include <corsika/media/HomogeneousMedium.hpp>
+#include <corsika/media/IMediumModel.hpp>
+#include <corsika/media/MediumProperties.hpp>
+#include <corsika/media/MediumPropertyModel.hpp>
+
+using namespace corsika;
+
+// Example to show how to construct an environment in CORSIKA
+
+// MediumType is constructed via "mixin inheritance"
+// Here, we construct our base class with IMediumModel and IMediumPropertyModel:
+// the former allow us define a density profile and nuclear composite,
+// the later is used to determine energy losses parameters.
+using IMediumType = IMediumPropertyModel<IMediumModel>;
+
+using EnvType = Environment<IMediumType>;
+
+int main() {
+  // define the environment and universe
+  EnvType env;
+  auto *universe = env.getUniverse().get();
+  auto const &rootCS = env.getCoordinateSystem();
+
+  // create a geometry object
+  Point const center{rootCS, 0_m, 0_m, 0_m};
+  auto radius = 1000_m;
+  auto sphere = std::make_unique<Sphere>(center, radius);
+
+  // create node from geometry object and put it into universe
+  auto node = std::make_unique<VolumeTreeNode<IMediumType>>(std::move(sphere));
+  universe->addChild(std::move(node));
+
+  // set media properties to our node, say it is water
+  auto nuc_comp =
+      NuclearComposition({{Code::Carbon, Code::Oxygen}, {0.11, 0.89}});
+  auto density = 1_g / (1_cm * 1_cm * 1_cm);
+  auto medium =
+      std::make_shared<MediumPropertyModel<HomogeneousMedium<IMediumType>>>(
+          Medium::WaterLiquid, density, nuc_comp);
+
+  node->setModelProperties(medium);
+
+  // example to explore the node
+  for (LengthType h = 0_m; h < radius; h += 100_m) {
+    Point const ptest{rootCS, 0_m, 0_m, h};
+    auto rho = env.getUniverse()
+                   ->getContainingNode(ptest)
+                   ->getModelProperties()
+                   .getMassDensity(ptest);
+    CORSIKA_LOG_INFO("radius: {:.2f} m, density: {:.2f} g/cm^3, ", h / 1_m,
+                     rho / 1_g * (1_cm * 1_cm * 1_cm));
+  }
+
+  return 0;
+}
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