ALICE3: Add method to get the TRK layer id

Author: mpuccio

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

@@ -89,7 +89,8 @@ class GeometryTGeo : public o2::detectors::DetMatrixCache
   int getSubDetID(int index) const;
   int getPetalCase(int index) const;
   int getDisk(int index) const;
-  int getLayer(int index) const;
+  int getLayer(int index) const;         ///< local layer index within the sub-detector (0-based per VD/MLOT)
+  int getLayerTRK(int index) const;   ///< global layer index across the full TRK (VD layers 0..nVD-1, MLOT layers nVD..nTotal-1)
   int getStave(int index) const;
   int getHalfStave(int index) const;
   int getModule(int index) const;

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

@@ -203,6 +203,15 @@ int GeometryTGeo::getLayer(int index) const
   return -1; /// -1 if not found
 }
 //__________________________________________________________________________
+int GeometryTGeo::getLayerTRK(int index) const
+{
+  if (getDisk(index) != -1) {
+    return -1; /// disks do not have a global layer index
+  }
+  int subDetID = getSubDetID(index);
+  return subDetID * o2::trk::constants::VD::petal::nLayers + getLayer(index); // MLOT: offset by number of VD layers
+}
+//__________________________________________________________________________
 int GeometryTGeo::getStave(int index) const
 {
   int subDetID = getSubDetID(index);