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CATIA-GDML Geometry Builder. S. Belogurov 1,2 (, Yu. Berchun 2 , A. Chernogorov 1 , P. Malzacher 3 , E. Ovcharenko 1,2 , A. Semennikov 1. 1- Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia

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Catia gdml geometry builder
CATIA-GDML Geometry Builder

S. Belogurov1,2(, Yu. Berchun2, A. Chernogorov1, P. Malzacher3, E. Ovcharenko1,2, A. Semennikov1

1- Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia

2- Bauman Moscow State Technical University, (BMSTU) Moscow, Russia

3- GSI - Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany


The problem

The task



Geometry representation in CAD and G4/ROOT

The difference is twofold: in the description of solid bodies and in the hierarchy of assemblies.

Design optimization of complex, densely packed systems in severe radiation conditions (lke FAIR experiments) requires iterative exchange of geometry and material info


L2(Box2, Plastic

, L3, 2L4)

Solids: CSG vs. “arbitrary”

CAD system

simulation tools


In CAD hierarchy a minimal unit is a solid body (part).

Products (assemblies) and subproducts are only logical units – all the materials are assigned to solid bodies inside the part files or to parts

  • In the G4/ROOT hierarchy there are three conceptual layers:

    • - G4VSolid: shape, size

    • - G4LogicalVolume: material, MF, sensitivity,

    • daughter volumes, etc.

    • - G4VPhysicalVolume: position and rotation of

    • an instance of the logical volume inside its mother

For mechanical, thermal, and some of electromagnetic software the transfer is automated.For radiation simulation packages that’s not a case.

In some cases automated geometry transfer is possible, but result is not optimized for simulations and computations are too slow for big assemblies and complex shapes.

The method

Implementation of primitives as parameterized User Defined Features (UDF) in CATIA.

The UDFs are placed into G4Catalog.

For realization of Boolean combinations CATIA operations Add, Remove and Intersect are used.

3 methods of multiple instantiation are implemented

Replica - matches with G4ReplicaVol

Array - copied objects can be inserted into an intermediate logical volume

SimplePlacement Array - intermediate volume is only a convenient reference frame

File structure for representation of a LogicalVolume.

PartBody contains a parameterized solid and material form G4Material CATIA catalog.

Unparameterized solid copy of the PartBody is published

Solids, published in files corresponding to smaller LogicalVolumes can be inserted into the tree with positioning. They represent daughter volumes

1. Implement G4 – like geometry in CATIA2. Extend construction and measurement functionality of CATIA by special tools for building G4 – like representation of the existing CAD model3. Make simulation optimized geometry4. Exchange geometry via GDML


Running export Macro





LHCb VELO read from GDML

Avoid unions

Required detalization

Use material of mother volumes


Simple bodies

Crystal calorimeter for R3B

GLAD for R3B

Consists of 4 SS and Cu layers of complicated shapes with ribs.

All transferred to G4/ROOT. One of the shells is discussed here

General and partial views of the crystal array for R3B calorimeter

Cylinders, Tori, and Ellipsoids:

General shape is OK, but the shell has slits – bad for simulations 

Radii and heights of cylinders are modified, Ellipsoid -> Sphere, but no slits: good for simulations 

G4/ROOT-like representation of a slice of CFC boxes and entire crystal array

  • Illustration of the procedure.

  • Three Part files are loaded.

  • Slice is twice inserted and positioned inside the Cylinder

  • Cylinder is positioned inside the World (Box)

  • Geometry exported to GDML and read by ROOT


- Enhancement of the set of implemented primitives

- Improvement of the G4Materials catalog in CATIA

- Implementation of checkers for CSG tree structure and volume overlaps

- Adaptation of the CATIA Digital Mockup (DMU) optimizer for automatic fit of parameterized CSG models to existing parts

- Case study and best practice elaboration


The authors are grateful to Drs. F. Carminati, R. Brun, A. Gheata (CERN), and D. Bertini (GSI) for stimulating interest and discussions and to A. Markin (BMSTU) for his contribution into the project. The work was supported by INTAS grant 06-1000012-8778and by FAIR-Russia Recearch Center.