Create the script GDMLROOT.py and put it in $ROOTSYS/gdml. It should contain the following code.
import sys
import xml.sax
import ROOT
import ROOTBinding
import GDMLContentHandler
ROOT.gSystem.Load("libGeom")
gdmlhandler = GDMLContentHandler.GDMLContentHandler(ROOTBinding.ROOTBinding())
filename = 'test.gdml'
if sys.argv.__len__() > 1:
filename = sys.argv[1]
xml.sax.parse(filename, gdmlhandler)
geomgr = ROOT.gGeoManager
geomgr.SetTopVolume(gdmlhandler.WorldVolume())
geomgr.CloseGeometry()
geomgr.DefaultColors()
geomgr.SetExplodedView(1)
geomgr.SetBombFactors(5.0,5.0,5.0,5.0)
gdmlhandler.WorldVolume().Draw("ogl")
This command takes a GDML file as its argument. Otherwise, it uses the default of test.gdml.
python -i GDMLROOT.py mygeom.gdml