modified: gem_tracker.xml

	new file:   scripts/tutorial1_hit_position.cxx

gem_tracker.xml

@@ -93,9 +93,14 @@
 
   <readouts>
     <readout name="GEMTrackerHits">
-      <segmentation type="PolarGridRPhi" grid_size_phi="1.0*degree" grid_size_r="1.0*cm"/>
+      <segmentation type="CartesianGridXY" grid_size_x="1*cm" grid_size_y="3*cm" />
+      <id>system:8,barrel:2,layer:4,module:12,sensor:2,x:32:-16,y:-16</id>
+      <!--
+      <segmentation type="PolarGridRPhi" grid_size_phi="5.0*degree" grid_size_r="1.0*cm"/>
       <id>system:5,barrel:3,layer:4,module:5,r:32:-16,phi:-16</id>
-      </readout>
+      -->
+    </readout>
+
   </readouts>
 
   <!--

scripts/tutorial1_hit_position.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 tutorial1_hit_position(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);
+
+  // 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());
+      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 = h.position;
+                        if (std::hypot(pos.x,pos.y) > 30.0) {
+                          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");
+}