Introduction

The Geant4 geometry XML convertor is a small set of C++ classes that are included in the Geant4 Virtual Monte Carlo . It enables to generate XML files with geometry description in the AGDD or GDML format. The geometry can be then browsed and visualized using GraXML tool .

How to generate XML files from Geant4 VMC

1. Start root and run example E02:
   cd geant4_vmc/examples/E02
   root.exe
   root[0] .x run_g4.C
   
   
2. Go to Geant4 UI:
   root [1] ((TGeant4*)gMC)->StartGeantUI()
   
   
3. Invoke Geant4 UI command:
   Idle> /xml/generateAGDD [volName] or
   Idle> /xml/generateGDML [volName]
   
   A file "WRLD.xml" or "WRLD.gdml" will be generated. If a volume name is specified after the command:
   the XML file "volName.xml" or "volName.gdml" will be then genarated for the specified volume and its daughters tree.
   

How to include XML convertor in standard Geant4 application

E.g. in the Geant4 novice example N02:

1. Add these lines to GNUmakefile:
   # added lines
   CPPFLAGS   +=  -I/mypath/geant4_vmc/convertors/g4toxml/include
   EXTRALIBS   +=  -L/mypath/geant4_vmc/lib/tgt_Linux   -lg4toxml
   
   
2. Include TG4AGDDGeometryGenerator and/or TG4GDMLGeometryGenerator instance in ExN02DetectorConstruction.hh:
   
   #include "TG4AGDDGeometryGenerator.h"
   #include "TG4GDMLGeometryGenerator.h"
      // ... skipped
   private:
      // ... skipped
      TG4AGDDGeometryGenerator    fAGDDGeometryGenerator;
      TG4GDMLGeometryGenerator    fGDMLGeometryGenerator;
   };
   

How to browse and visualize XML files with GraXML

GraXML is a program for the 3D visualization of the Event and Detector description data. It uses Java3D to create, render and manipulate SceneGraph and can be run as a standalone application.
Variety of pictures created by GraXML can be found in the GraXML Gallery .

In order to view a file (or files) generated by Geant4 VMC XML convertor in GraXML do the following steps:

1. If using AGDD, copy the AGDD.dtd file from the GraXML distribution (GraXML/misc/Test/AGDD.dtd) to your current directory
   
   
2. Set the Java environment and run GraXML following the instructions in the GraXML Guide .
   
   
3. In the GraXML window type command:
   w.show("myfile.xml"); or
   w.show("myfile.gdml");

A few tips how to start:

• When viewing the XML file in a text editor select XML (if available) or HTML (otherwise) syntax highlighting.
• When viewing a "huge" geometry use high optimisation level via Config.setOptimisation(9); command (viewing with limited interactivity).

XML Formats

• Atlas AGDD (Detector description)
  


• GDML (Geometry Description Markup Language)
  

Differences in GEANT3, Geant4 and XML Geometry Description

• In GEANT3 a volume (e.g. XYZ) can change its solid parameters with its new position (placement with GSPOSP); for each such G3 volume with modified solid parameters a new G4LogicalVolume (associated with a new G4VSolid) is defined in Geant4 and a new element with name XYZ_N in XML.
  
  
• Divided volumes (defined by GSDVN, GSDVN2, GSDVT, GSDVT2) in GEANT3 are in Geant4 represented by replicated volumes (G4PVReplica) and in XML (AGDD) with "mpos.." elements. GDML does not support divided or replicated volumes yet.
  
  
• In AGDD, for each volume (e.g. XYZ) that contains daughters volumes a new composition element is created with the name XYZ_comp and it is placed separately from the volume's solid.
  So for each placement of this volume two XML elements are created:
  1. a "pos.." (or "transform") element that places the volume's solid XYZ
  2. a "pos.." (or "transform") element that places the volume's daughters XYZ_comp.
  This doubling is not present in GDML.

XML Web pages

• GDML
• XML in Atlas
• LHCb Detector Decription