add optional SD to combine hits

Simulation/DetSimSD/src/GenericTrackerSensDetTool.cpp

@@ -5,6 +5,7 @@
 #include "DD4hep/Detector.h"
 
 #include "GenericTrackerSensitiveDetector.h"
+#include "TrackerCombineSensitiveDetector.h"
 
 #include "CLHEP/Units/SystemOfUnits.h"
 
@@ -33,8 +34,14 @@ G4VSensitiveDetector* GenericTrackerSensDetTool::createSD(const std::string& nam
   debug() << "createSD for " << name << endmsg;
   
   dd4hep::Detector* dd4hep_geo = m_geosvc->lcdd();
-
-  G4VSensitiveDetector* sd = new GenericTrackerSensitiveDetector(name, *dd4hep_geo);
+  auto sens = dd4hep_geo->sensitiveDetector(name);
+  G4VSensitiveDetector* sd = nullptr;
+  if(sens.combineHits()){
+    sd = new TrackerCombineSensitiveDetector(name, *dd4hep_geo);
+  }
+  else{
+    sd = new GenericTrackerSensitiveDetector(name, *dd4hep_geo);
+  }
 
   return sd;
 }