new file: scripts/tutorial3_id_spec.cxx

scripts/tutorial3_id_spec.cxx

+R__LOAD_LIBRARY(libfmt.so)
+#include "fmt/core.h"
+
+#include "Math/Vector3D.h"
+#include "Math/Vector4D.h"
+#include "Math/VectorUtil.h"
+
+#include "ROOT/RDataFrame.hxx"
+#include "TCanvas.h"
+#include "TChain.h"
+#include "TF1.h"
+#include "TFile.h"
+#include "TH1D.h"
+#include "TH1F.h"
+#include "TLegend.h"
+#include "TMath.h"
+#include "TRandom3.h"
+#include "TTree.h"
+
+#include <algorithm>
+#include <iterator>
+#include <tuple>
+#include <vector>
+#include <cmath>
+
+#include "DD4hep/Detector.h"
+#include "DDRec/CellIDPositionConverter.h"
+
+#include "dd4pod/Geant4ParticleCollection.h"
+#include "dd4pod/TrackerHitCollection.h"
+
+/** Hit position example.
+ *
+ */
+void tutorial2_cell_size(const char* fname = "gem_tracker_sim.root") {
+  using namespace ROOT::Math;
+
+  TChain* t = new TChain("events");
+  t->Add(fname);
+
+  ROOT::RDataFrame d0(*t, {"GEMTrackerHits", "MCParticles"});
+  //std::cout << d0.DescribeDataset() << std::endl;
+
+  // -------------------------
+  // Get the DD4hep instance
+  // Load the compact XML file
+  // Initialize the position converter tool
+  dd4hep::Detector& detector = dd4hep::Detector::getInstance();
+  detector.fromCompact("gem_tracker.xml");
+  dd4hep::rec::CellIDPositionConverter cellid_converter(detector);
+
+  auto decoder = detector.readout("GEMTrackerHits").idSpec().decoder();
+  fmt::print("{}\n", decoder->fieldDescription());
+  auto layer_index = decoder->index("layer");
+  fmt::print(" layer index is {}.\n", layer_index);
+
+  // Simple lambda to define nhits branch
+  auto nhits = [](const std::vector<dd4pod::TrackerHitData>& evt) { return (int)evt.size(); };
+
+  auto local_position = [&](const std::vector<dd4pod::TrackerHitData>& hits) {
+    std::vector<std::array<double, 2>> result;
+    for (const auto& h : hits) {
+      // The actual hit position:
+      auto pos0 = (h.position);
+
+      // **This is the most important part.** It provides a way of getting the
+      // geometry information in a flexible way.
+      // The segmentation hit postion:
+      auto pos1 = cellid_converter.position(h.cellID);
+      fmt::print("              Hit Position : {},{},{}\n", pos0.x / 10.0, pos0.y / 10.0, pos0.z / 10.0);
+      fmt::print("Segmentation-Cell Position : {},{},{}\n", pos1.x(), pos1.y(), pos1.z());
+
+      auto context = cellid_converter.findContext( h.cellID ) ;
+      dd4hep::Readout r  = cellid_converter.findReadout( context->element ) ;
+      dd4hep::Segmentation seg = r.segmentation() ;
+      auto cell_dim = seg.cellDimensions(h.cellID);
+      std::cout << " dim ";
+      for(const auto& dim : cell_dim) {
+        std::cout << dim << ", ";
+      }
+      std::cout << "\n";
+
+      result.push_back({pos0.x / 10.0 - pos1.x(), pos0.y / 10.0 - pos1.y()});
+    }
+    return result;
+  };
+
+  auto x_pos = [&](const std::vector<std::array<double, 2>>& xypos) {
+    std::vector<double> result;
+    for (const auto& h : xypos) {
+      result.push_back(h.at(0));
+    }
+    return result;
+  };
+  auto y_pos = [&](const std::vector<std::array<double, 2>>& xypos) {
+    std::vector<double> result;
+    for (auto h : xypos) {
+      result.push_back(h.at(1));
+    }
+    return result;
+  };
+
+  auto d1 = d0.Define("nhits", nhits, {"GEMTrackerHits"})
+                .Filter([=](const std::vector<dd4pod::TrackerHitData>& hits) {
+                      for (auto h : hits) {
+                        auto pos = ROOT::Math::XYZVector(h.position.x,h.position.y,h.position.z);
+                        if ((pos.r() > 100.0) && (std::abs(pos.phi()-M_PI/2.0)< M_PI/6)) {
+                          return true;
+                        }
+                      }
+                      return false;
+                    },
+                    {"GEMTrackerHits"})
+                .Define("xy_hit_pos", local_position, {"GEMTrackerHits"})
+                .Define("x_pos", x_pos, {"xy_hit_pos"})
+                .Define("y_pos", y_pos, {"xy_hit_pos"});
+
+  auto h_local_pos = d1.Histo2D(TH2D("h_local_pos", ";x [cm]; y [cm] ", 100, -5.0, 5.0, 100, -5.0, 5.0), "x_pos", "y_pos");
+
+  TCanvas* c = new TCanvas();
+  h_local_pos->DrawClone("colz");
+  c->SaveAs("results/hit_position.png");
+}