change position from first contribution to cell center

Simulation/DetSimSD/include/DetSimSD/DDG4SensitiveDetector.h

@@ -52,6 +52,8 @@ public:
     //  from the current sensitive volume to the world volume
     virtual long long getCellID(const G4Step* step);
 
+    // Returns the position of center of cell
+    virtual dd4hep::Position getNominalPosition(const G4Step* step, const long long cellID=0);
 
 protected:
     /// Reference to the detector description object

Simulation/DetSimSD/src/CaloSensitiveDetector.cpp

@@ -48,7 +48,12 @@ CaloSensitiveDetector::ProcessHits(G4Step* step, G4TouchableHistory*) {
     }
     //    G4cout << "----------- Geant4GenericSD<Calorimeter>::buildHits : position : " << pos << G4endl;
     if ( !hit ) {
-        hit = new CalorimeterHit(pos);
+        // not applicable for segmentation case
+        //G4ThreeVector local(0,0,0);
+        //G4ThreeVector global = h.preTouchable()->GetHistory()->GetTopTransform().InverseTransformPoint(local);
+        //hit = new CalorimeterHit(dd4hep::Position(global.x(), global.y(), global.z()));
+        dd4hep::Position posCellCenter = getNominalPosition(step, id);
+        hit = new CalorimeterHit(posCellCenter);
         hit->cellID  = id; //getCellID( step );
         m_hc->insert(hit);
 	if(m_isMergeEnabled) m_hitMap[id] = hit;

Simulation/DetSimSD/src/DDG4SensitiveDetector.cpp

@@ -19,7 +19,8 @@
 
 // convert from CLHEP to DD4hep
 static const double MM_2_CM = (dd4hep::millimeter/CLHEP::millimeter);
-
+// convert from DD4hep to CLHEP
+static const double CM_2_MM = (CLHEP::millimeter/dd4hep::millimeter);
 
 DDG4SensitiveDetector::DDG4SensitiveDetector(const std::string& name, dd4hep::Detector& description)
     : G4VSensitiveDetector(name), m_detDesc(description),
@@ -73,3 +74,15 @@ DDG4SensitiveDetector::getCellID(const G4Step* step) {
     }
     return volID;
 }
+
+dd4hep::Position
+DDG4SensitiveDetector::getNominalPosition(const G4Step* step, long long cellID) {
+    if(cellID==0) cellID = getCellID(step);
+    dd4hep::sim::Geant4StepHandler h(step);
+    dd4hep::Segmentation        seg    = m_readout.segmentation();
+    dd4hep::Position loc(0,0,0);
+    if ( seg.isValid() ) loc = seg.position(cellID);
+    G4ThreeVector local(loc.x()*CM_2_MM, loc.y()*CM_2_MM, loc.z()*CM_2_MM);
+    G4ThreeVector global = h.preTouchable()->GetHistory()->GetTopTransform().InverseTransformPoint(local);
+    return dd4hep::Position(global.x(), global.y(), global.z());
+}