Added generic RectangularTracker construction

	new file:   compact/B0_tracker.xml
	modified:   compact/definitions.xml
	modified:   reference_detector.xml
	new file:   src/ref_RectangularTracker_geo.cpp

compact/B0_tracker.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<lccdd>
+  <define>
+    <comment>
+      ---------------------------------
+      Far Forward B0 Tracker Parameters
+      ---------------------------------
+    </comment>
+    <constant name="B0Tracker_zpos" value="B0PF_CenterPosition + B0PF_Length/2.0 + 20.0*cm"/>
+  </define>
+
+  <detectors>
+    <detector 
+      id="B0Tracker_ID"
+      name="B0Tracker"
+      readout="B0TrackerHits" 
+      type="ref_RectangularTracker"
+      insideTrackingVolume="true"
+      reflect="false"
+      vis="Argonne_Red">
+      <position x="0" y="0" z="B0Tracker_zpos"/>
+      <layer id="1" 
+        vis="Argonne_Blue"
+        x="20.0*cm" 
+        y="10.0*cm" >
+        <slice material="Air" thickness="1.0*cm" vis="Argonne_Blue" sensitive="true" />
+        <slice material="Air" thickness="1.0*cm" vis="Argonne_Blue" sensitive="true" />
+        <slice material="Air" thickness="1.0*cm" vis="Argonne_Blue" sensitive="true" />
+        <slice material="Air" thickness="1.0*cm" vis="Argonne_Blue" sensitive="true" />
+      </layer>
+    </detector>
+  </detectors>
+
+  <readouts>
+    <readout name="B0TrackerHits">
+      <segmentation type="CartesianGridXY" grid_size_x="1.0*mm" grid_size_y="1.0*mm" />
+      <id>system:8,barrel:3,layer:4,slice:4,x:32:-16,y:-16</id>  
+    </readout>
+  </readouts>
+
+</lccdd>

compact/definitions.xml

@@ -235,11 +235,13 @@
       (150-169) Far Forward  Detectors
       =====================================
 
-      Forward Roman Pot ID: 150
-      Zero Degree Cal.  ID: 160
+      Forward Roman Pot  ID: 150
+      Forward B0 Tracker ID: 151
+      Zero Degree Cal.   ID: 160
 
     </comment>
     <constant name="ForwardRomanPot_ID" value="150"/>
+    <constant name="B0Tracker_ID"       value="151"/>
     <constant name="ffi_ZDC_ID"         value="160"/>
 
     <comment> 

reference_detector.xml

@@ -124,6 +124,7 @@
   <include ref="compact/ci_GEM.xml"/>
   <include ref="compact/hcal.xml"/>
   <include ref="compact/forward_trd.xml"/>
+  <include ref="compact/B0_tracker.xml"/>
   <!--
   <include ref="compact/ci_HCAL.xml"/>
   <include ref="compact/forward_rich.xml"/>

src/ref_RectangularTracker_geo.cpp

+//==========================================================================
+//  AIDA Detector description implementation 
+//--------------------------------------------------------------------------
+// Copyright (C) Organisation europeenne pour la Recherche nucleaire (CERN)
+// All rights reserved.
+//
+// For the licensing terms see $DD4hepINSTALL/LICENSE.
+// For the list of contributors see $DD4hepINSTALL/doc/CREDITS.
+//
+// Author     : M.Frank
+// Modified   : W.Armstrong
+//
+//==========================================================================
+//
+// Specialized generic detector constructor
+// 
+//==========================================================================
+#include "DD4hep/DetFactoryHelper.h"
+
+using namespace std;
+using namespace dd4hep;
+using namespace dd4hep::detail;
+
+static Ref_t create_detector(Detector& description, xml_h e, SensitiveDetector sens)  {
+  xml_det_t  x_det     = e;
+  Material   air       = description.air();
+  string     det_name  = x_det.nameStr();
+  bool       reflect   = x_det.reflect();
+  DetElement sdet(det_name,x_det.id());
+  Assembly   assembly(det_name);
+  PlacedVolume pv;
+  int l_num = 0;
+  xml::Component  pos  = x_det.position();
+
+  for(xml_coll_t i(x_det,_U(layer)); i; ++i, ++l_num)  {
+    xml_comp_t x_layer    = i;
+    string     l_nam      = det_name + _toString(l_num, "_layer%d");
+    double     x_lay      = x_layer.x();
+    double     y_lay      = x_layer.y();
+    double     z          = 0;
+    double     zmin       = 0;
+    double     layerWidth = 0.;
+    int        s_num      = 0;
+    for(xml_coll_t j(x_layer,_U(slice)); j; ++j)  {
+      double thickness = xml_comp_t(j).thickness();
+      layerWidth += thickness;
+    }
+    Box    l_box(x_lay/2.0, y_lay/2.0, layerWidth/2.0 );
+    Volume l_vol(l_nam, l_box, air);
+    l_vol.setVisAttributes(description, x_layer.visStr());
+    for (xml_coll_t j(x_layer, _U(slice)); j; ++j, ++s_num) {
+      xml_comp_t x_slice = j;
+      double     thick   = x_slice.thickness();
+      Material   mat     = description.material(x_slice.materialStr());
+      string     s_nam   = l_nam + _toString(s_num, "_slice%d");
+      Volume     s_vol(s_nam, Box(x_lay/2.0, y_lay/2.0, thick/2.0), mat);
+      if (x_slice.isSensitive()) {
+        sens.setType("tracker");
+        s_vol.setSensitiveDetector(sens);
+      }
+      s_vol.setAttributes(description, x_slice.regionStr(), x_slice.limitsStr(), x_slice.visStr());
+      pv = l_vol.placeVolume(s_vol, Position(0, 0, z - zmin - layerWidth / 2 + thick / 2));
+      pv.addPhysVolID("slice", s_num);
+    }
+
+    DetElement layer(sdet,l_nam+"_pos",l_num);
+    pv = assembly.placeVolume(l_vol,Position(0,0,zmin+layerWidth/2.));
+    pv.addPhysVolID("layer",l_num);
+    pv.addPhysVolID("barrel",1);
+    layer.setPlacement(pv);
+    if ( reflect )  {
+      pv = assembly.placeVolume(l_vol,Transform3D(RotationY(M_PI),Position(0,0,-zmin-layerWidth/2)));
+      pv.addPhysVolID("layer",l_num);
+      pv.addPhysVolID("barrel",2);
+      DetElement layerR = layer.clone(l_nam+"_neg");
+      sdet.add(layerR.setPlacement(pv));
+    }
+  }
+  if ( x_det.hasAttr(_U(combineHits)) ) {
+    sdet.setCombineHits(x_det.attr<bool>(_U(combineHits)),sens);
+  }
+  pv = description.pickMotherVolume(sdet).placeVolume(assembly,Position(pos.x(),pos.y(),pos.z()));
+  pv.addPhysVolID("system", x_det.id());      // Set the subdetector system ID.
+  sdet.setPlacement(pv);
+  return sdet;
+}
+
+DECLARE_DETELEMENT(ref_RectangularTracker,create_detector)