[ALICE3] TRK: Collect services in a dedicated volume assembly (#15215)

* Refactor TRKServices to use volume assembly

* Add service volume name to GeometryTGeo

* Add getTRKServiceVolPattern method and variable

Author: njacazio

Detectors/Upgrades/ALICE3/TRK/base/include/TRKBase/GeometryTGeo.h

@@ -43,6 +43,7 @@ class GeometryTGeo : public o2::detectors::DetMatrixCache
     return sInstance.get();
   };
   static const char* getTRKVolPattern() { return sVolumeName.c_str(); }
+  static const char* getTRKServiceVolPattern() { return sServiceVolName.c_str(); }
   static const char* getTRKLayerPattern() { return sLayerName.c_str(); }
   static const char* getTRKPetalAssemblyPattern() { return sPetalAssemblyName.c_str(); }
   static const char* getTRKPetalPattern() { return sPetalName.c_str(); }
@@ -198,6 +199,7 @@ class GeometryTGeo : public o2::detectors::DetMatrixCache
   static constexpr int MAXLAYERS = 20; ///< max number of active layers
 
   static std::string sVolumeName;
+  static std::string sServiceVolName;
   static std::string sLayerName;
   static std::string sPetalAssemblyName;
   static std::string sPetalName;

Detectors/Upgrades/ALICE3/TRK/base/src/GeometryTGeo.cxx

@@ -26,6 +26,7 @@ std::unique_ptr<o2::trk::GeometryTGeo> GeometryTGeo::sInstance;
 
 // Names
 std::string GeometryTGeo::sVolumeName = "TRKV";
+std::string GeometryTGeo::sServiceVolName = "TRKService";
 std::string GeometryTGeo::sLayerName = "TRKLayer";
 std::string GeometryTGeo::sPetalAssemblyName = "PETAL";
 std::string GeometryTGeo::sPetalName = "PETALCASE";

Detectors/Upgrades/ALICE3/TRK/simulation/src/TRKServices.cxx

@@ -127,18 +127,21 @@ void TRKServices::createMaterials()
 
 void TRKServices::createServices(TGeoVolume* motherVolume)
 {
+
+  TGeoVolumeAssembly* vol = new TGeoVolumeAssembly(GeometryTGeo::getTRKServiceVolPattern());
+  motherVolume->AddNode(vol, 2, new TGeoTranslation(0, 0., 0));
   createMaterials();
   createVacuumCompositeShape();
   auto& trkPars = TRKBaseParam::Instance();
   if (trkPars.getLayoutSRV() == kLOISymm) {
     LOGP(info, "TRK services: LoI version");
-    createMiddleServices(motherVolume);
-    createOuterDisksServices(motherVolume);
-    createOuterBarrelServices(motherVolume);
+    createMiddleServices(vol);
+    createOuterDisksServices(vol);
+    createOuterBarrelServices(vol);
   } else {
     LOGP(info, "TRK services: Peacock layout");
-    createMLServicesPeacock(motherVolume);
-    createOTServicesPeacock(motherVolume);
+    createMLServicesPeacock(vol);
+    createOTServicesPeacock(vol);
   }
 }