The $ROOTSYS/gdml directory contains a set of Python modules designed
for processing (reading in as well as writing out) Geometry
Description Markup Language (GDML) files. They act as a converter
between the GDML geometry files and the TGeo geometry structures (and
vice versa).

GDML->ROOT
----------

The GDML to TGeo converter uses the xml.sax module for parsing
XML. The GDMLContentHandler module contains a concrete implementation
of xml.sax.ContentHandler, specific for GDML processing. In addition
to the standard methods used by the parser (startElement and
endElement), the GDMLContentHanler class also two additional methods:
WorldVolume method and AuxiliaryData method. The WorldVolume method
allows the user to access the top volume object (the top of the
geometry tree) once the parsing is finished. The AuxiliaryData method
returns the map of auxiliary (optional) attributes (like colour,
visibility, sensitive detectors, etc) associated to any volume. The
GDMLContentHandler requires two other modules for processing the GDML
file: the 'processes' module and the 'ROOTBinding' module. The
'processes' module contains specific methods (processes) for each of
the GDML elements. These methods then use particular 'binding' (in our
case ROOTBinding) in order to instanciate the appropriate geometry
(TGeo) object. Please refere to the comment part of ROOTBinding.py
file for the list of supported TGeo classes.

The GDML to ROOT converter is now interfaced to the
TGeoManager::Import method which automatically calls the appropriate
Python scripts whenever a file with .gdml extension is given as
argument.

Alternatively, one can also use GDML->ROOT converter directly from the
Python prompt, for instance:

###################
import sys
import xml.sax
import ROOT
import ROOTBinding
import GDMLContentHandler
 
ROOT.gSystem.Load("libGeom")
 
gdmlhandler = GDMLContentHandler.GDMLContentHandler(ROOTBinding.ROOTBinding())
 
xml.sax.parse('mygeometry.gdml', gdmlhandler)
geomgr = ROOT.gGeoManager
 
geomgr.SetTopVolume(gdmlhandler.WorldVolume())
geomgr.CloseGeometry()
geomgr.DefaultColors()
 
gdmlhandler.WorldVolume().Draw("ogl")
###################

where 'mygeometry.gdml' should be replace by the name of the GDML file
to be read.


ROOT->GDML
----------

The TGeo to GDML converter allows to export ROOT geometries (TGeo
geometry trees) as GDML files. The writer module writes a GDML file
out of the 'in-memory' representation of the geometry. The actual
application-specific (ROOT) binding is implemeted in ROOTwriter
module. It contains 'binding methods' for TGeo geometry classes which
can be exported in GDML format. Please refere to the comment part of
the ROOTwriter.py file for the list of presently supported TGeo
classes. The ROOTwriter class contains also three methods,
dumpMaterials, dumpSolids and examineVol which need to be called in
order to export materials, solids and geometry tree respectively. 

The TGeo to GDML converter is now interfaced to the
TGeoManager::Export method which automatically calls the appropriate
Python scripts whenever the geometry output file has the .gdml
extension. 

Alternatively, one can also use the ROOT->GDML converter directly from
the Python prompt (assuming the TGeo geometry has already been loaded
into memory in one or another way), for example:

###################
from math import *
from units import *
 
import ROOT
import writer
import ROOTwriter
 
# get TGeoManager and
# get the top volume of the existing (in-memory) geometry tree
geomgr = ROOT.gGeoManager
topV = geomgr.GetTopVolume()
 
# instanciate writer
gdmlwriter = writer.writer('mygeo.gdml')
binding = ROOTwriter.ROOTwriter(gdmlwriter)
 
# dump materials
matlist = geomgr.GetListOfMaterials()
binding.dumpMaterials(matlist)
 
# dump solids
shapelist = geomgr.GetListOfShapes()
binding.dumpSolids(shapelist)
 
# dump geo tree
print 'Traversing geometry tree'
gdmlwriter.addSetup('default', '1.0', topV.GetName())
binding.examineVol(topV)
 
# write file
gdmlwriter.writeFile()
###################



For any questions or comments about those converters as well as about
GDML in general please email Witold.Pokorski@cern.ch.