1. Witek Pokorski, Radovan Chytracek, Jeremy McCormick, Giovanni Santin
Geometry Description Markup Language and its application-specific bindings
Witek Pokorski, Radovan Chytracek, Jeremy McCormick, Giovanni Santin
CHEP06, Mumbai, India
W. Pokorski - CERN
Simulation Project

2. Outline Background GDML Schema GDML readers/writers Some examples
Conclusion
W. Pokorski - CERN
Simulation Project

3. GDML - Motivation
simulation toolkits come with their native geometry description formats
many (most?) of the users do not implement geometry in those formats
users use their own geometry description formats providing more flexibility
integral parts of experiment software frameworks
cannot be easily exported in application independent way
therefore GDML has been developed
to have an application independent and flexible geometry format
to be able to interchange geometry between different applications for the purpose of
physics validation/comparison, visualization, debugging
W. Pokorski - CERN
Simulation Project

4. GDML design choice - why XML?
purpose of GDML is to describe data
to provide persistent form of geometry data
not procedural, but markup language
must be easy to read and write
no heavy I/O system to read GDML
format must be application independent
possibility to edit/read geometry files is an advantage
XML file can be edited using any editor
geometry can be modified easily
must be easy to extend and be modular
GDML designed as an application of XML
W. Pokorski - CERN
Simulation Project

5. GDML components GDML is defined through XML Schema (XSD)
XSD = XML based alternative to Document Type Definition (DTD)
defines document structure and the list of legal elements
XSD are in XML -> they are extensible
GDML can be written by hand or generated automatically
'GDML writer' allows writing-out GDML file
GDML needs 'reader'
'GDML reader' creates 'in-memory' representation of the geometry description
user application (1)
GDML writer
GDML
Schema
GDML file
GDML reader
user application (2)
W. Pokorski - CERN
Simulation Project

6. GDML Schema defines document structure and the list of legal elements
materials
material, isotope, element, mixture
solids
box, sphere, tube, cone, polycone, parallepiped, trapezoid, torus, polyhedra, hyperbolic tube, elliptical tube, ellipsoid
boolean solids
volumes
assembly volumes and reflections
replicas and divisions
parameterised volumes (position, rotation and size)
first implementation
W. Pokorski - CERN
Simulation Project

7. GDML document positions, rotations materials solids geometry tree
<?xml version="1.0" encoding="UTF-8"?>
<gdml xsi:noNamespaceSchemaLocation="GDMLSchema/gdml.xsd">
<define> …
<position name="TrackerinWorldpos" unit="mm" x="0" y="0" z="100"/>
</define>
<materials>
<material formula=" " name="Air" >
<D value="1.290" unit="mg/cm3"/>
<fraction n="0.7" ref="Nitrogen" />
<fraction n="0.3" ref="Oxygen" />
</material>
</materials>
<solids>
<box lunit="mm" name="Tracker" x="50" y="50" z="50"/>
</solids>
<structure>
<volume name="World" >
<materialref ref="Air" />
<solidref ref="world" />
<physvol>
<volumeref ref="Tracker" />
<positionref ref="TrackerinWorldpos"/>
<rotationref ref="TrackerinWorldrot"/>
</physvol>
</volume>
</structure>
<setup name="Default" version="1.0" >
<world ref="World" />
</setup>
</gdml>
positions, rotations
materials
solids
geometry tree
'world' volume
W. Pokorski - CERN
Simulation Project

8. GDML reader
give pointer to
world volume
reads geometry from GDML file and creates its application specific (ROOT or G4) representation in memory
most logic in application-independent part
light application-depended bindings
Application binding
(ROOT, G4)
Application
(ROOT, G4)
create material,
volume, etc…
XML Engine
(SAX)
GDML Schema
GDML file
W. Pokorski - CERN
Simulation Project

9. GDML writer
User Application
starting from 'in-memory' geometry tree (G4 or ROOT), generates the GDML file with that geometry
application independent part generating XML
containers for materials, solids, structure, etc
'light' application dependent bindings
scanning the geometry tree and adding elements to the containers
dump geometry
Application binding
(scanning tree)
add volume, etc
Document Builder
write document
GDML file
W. Pokorski - CERN
Simulation Project

10. CMS detector: G4->GDML->ROOT
~19000 physical volumes
snapshot provided by R.Maunder
thanks to Pedro Arce for help with running CMS simulation
W. Pokorski - CERN
Simulation Project

11. LHCb Detector: G4->GDML->ROOT
~5000 physical volumes
snapshot provided by R.Maunder
W. Pokorski - CERN
Simulation Project

12. Using GDML with Geant4 to write: to read: instantiate GDML writer
#include "WriterG4/G4GDMLWriter.h"
G4GDMLWriter g4writer("GDMLSchema/gdml.xsd", "g4test.gdml");
g4writer.DumpGeometryInfo(g4worldvolume);
to read:
SAXProcessor sxp;
sxp.Initialize();
ProcessingConfigurator config;
config.SetURI( "g4test.gdml" );
sxp.Configure( &config );
sxp.Run()
fWorld = (G4VPhysicalVolume *)
GDMLProcessor::GetInstance()->GetWorldVolume();
instantiate GDML writer
pass the 'top' volume to the writer
instantiate and configure the processor
get pointer to 'top' volume
W. Pokorski - CERN
Simulation Project

13. GDML processing - performance
GDML G4reader/G4writer (C++) tested on
complete LHCb and CMS geometries
parts of ATLAS geometry
problem with full ATLAS geometry - use of custom solids
for LHCb geometry (~5000 physical volumes)
writing out ~10 seconds (on P4 2.4GHz)
reading in ~ 5 seconds
file size ~2.7 Mb (~40k lines)
for CMS geometry (~19000 physical volumes)
writing out ~30 seconds
reading in ~15 seconds
file size ~7.9 Mb (~120k lines)
W. Pokorski - CERN
Simulation Project

14. GDML reader/writer in Python
Python - an interesting alternative to C++ for implementing the GDML processing code
dealing with XML in Python much easier (less code needed)
Python very good for 'glueing' different applications together
very easy interaction with C++ objects through generic Python bindings (PyROOT + Reflex)
used for G4->GDML->ROOT geometry exchange
enables running Geant4 + GDML reader/writer + ROOT from common Python prompt
W. Pokorski - CERN
Simulation Project

15. GDML for ROOT (in Python)
Python SAX parser
import xml.sax
import ROOT
import GDMLContentHandler
ROOT.gSystem.Load("libGeom")
geomgr = ROOT.TGeoManager("World","GDMLGeo")
gdmlhandler = GDMLContentHandler.GDMLContentHandler()
xml.sax.parse('test.gdml',gdmlhandler)
geomgr.SetTopVolume(gdmlhandler.WorldVolume())
geomgr.CloseGeometry()
gdmlhandler.WorldVolume().Draw()
PyROOT
GDML-specific parser extension
Standard TGeo
GDML parsing
get world volume from
GDMLContentHandler
W. Pokorski - CERN
Simulation Project

16. GDML facilitates physics validation
we want to compare Geant4 with FLUKA in the case of Atlas TileCal testbeam
we need a common geometry source
we have G4 geometry 'in-memory'
we export GDML
GDML binding added to FluGG (Fluka Geant4 Geometry interface)
FLUKA (FLUGG) job run with GDML geometry
GDML solves the problem of reimplementing geometry
W. Pokorski - CERN
Simulation Project

17. GDML as primary geometry source
Linear Collider - Jeremy McCormick, SLAC
Linear Collider Detector Description (LCDD) extends GDML with Geant4-specific information (sensitive detectors, physics cuts, etc)
GDML/LCDD is generic and flexible
several different full detector design concepts, including SiD, GLD, and LDC, where simulated using the same application
SiD
LDC
GLD
W. Pokorski - CERN
Simulation Project

18. GDML as primary geometry source
Space Research - Giovanni Santin, ESA
all geometry models for Geant4
component degradation studies (JWST, ConeXpress,...)
GRAS (Geant4 Radiation Analysis for Space)
enables flexible geometry configuration and changes
main candidate for CAD to G4 exchange format
ConeXpress
JWST NIRSpec
W. Pokorski - CERN
Simulation Project

19. GDML as primary geometry source
Anthropomorphic Phantom Project - Giorgio Guerrieri, Maria Grazia Pia, Susanna Guatelli, INFN
Modelization of the human body and anatomy for radioprotection studies
no hard-coded geometry, flexible configuration
W. Pokorski - CERN
Simulation Project

20. Future developement support for new solids handling of multiple files
'twisted' solids recently added to G4
handling of multiple files
enable splitting of GDML description into several files (containing different parts of the detector, etc)
W. Pokorski - CERN
Simulation Project

21. Conclusions
GDML is an application-independent, extensible geometry description language
GDML proving very useful as the geometry interchange format
geometries can be extracted from experiment-specific frameworks and then used in generic applications
physics validation
geometries can be moved between Geant4 and ROOT
geometry visualization using ROOT
GDML is used by several Geant4 users as the primary geometry description language
avoids hard-coding the geometry
allows running easily the same application with several different geometries
W. Pokorski - CERN
Simulation Project