Fix placement issue to get sensor materials inside the volume. This now means that the stave faces are not at local z=0 but instead at z=+-totalSensorMaterialThickness+0.1. Also fix global position bug since movement outwards is directional.

Author: JustusRudolph

Detectors/Upgrades/ALICE3/FT3/simulation/src/FT3Layer.cxx

@@ -450,7 +450,9 @@ void FT3Layer::createLayer(TGeoVolume* motherVolume)
     }
     // Finally put everything in the mother volume
     auto* FwdDiskRotation = new TGeoRotation("FwdDiskRotation", 0, 0, 180);
-    auto* FwdDiskCombiTrans = new TGeoCombiTrans(0, 0, mZ + z_local_offset, FwdDiskRotation);
+    // need to shift outwards always, so + forwards and - backwards
+    double z_offset_directional = mDirection ? z_local_offset : -z_local_offset;
+    auto* FwdDiskCombiTrans = new TGeoCombiTrans(0, 0, mZ + z_offset_directional, FwdDiskRotation);
 
     LOG(info) << "Inserting " << layerVol->GetName() << " inside " << motherVolume->GetName();
     motherVolume->AddNode(layerVol, 1, FwdDiskCombiTrans);

Detectors/Upgrades/ALICE3/FT3/simulation/src/FT3Module.cxx

@@ -538,13 +538,18 @@ void FT3Module::create_layout_staveGeo(double mZ, int layerNumber, int direction
    * Naturally, this will be mirrored for layers in the backwards direction,
    * such that the face of the sensors always face the interaction region.
    * 
-   * Currently, we stipulate that the default stave face is at local z
-   * that is slightly shifted by the air thickness encapsulating the layer
+   * Currently, we stipulate that the default stave face is at local z=0,
+   * that is then shifted by the half air thickness encapsulating the layer
    * to avoid overlaps with the air and services. All offsets are
    * calculated for backward direction (since that is a positive shift),
-   * and then flipped for forward.
+   * and then flipped for forward. At that point, the innermost/frontmost
+   * stave face is at the edge of the air volume, so we shift it back a little
+   * to make space for the sensor materials and a slight margin.
    */
-  double z_offset_to_carbon_face = z_offset_local;
+  double totalSensorMaterialThickness =
+    Constants::epoxyThickness + Constants::kaptonThickness + Constants::copperThickness +
+    Constants::epoxyThickness + Constants::siliconThickness;
+  double z_offset_to_carbon_face = z_offset_local - totalSensorMaterialThickness - 0.1;
   double z_offset_to_glue_Ka =
     z_offset_to_carbon_face + Constants::epoxyThickness / 2;
   double z_offset_to_kapton =