FreeCAD's python Importer & Exporter for GDML files.

Install by use of FreeCAD Addon Manager

Needs lxml which should be installed as part of FreeCAD

• FreeCAD_0.19.19424 and above.
• FreeCAD_0.19.19409_x64_Conda_Py3QT5-WinVS2015.7z and above.

There are known problems with FreeCAD 0.18 it is recommended that you use FreeCAD 0.19 as above. ( Note: You can install both versions 0.18 & 0.19 and still use 0.18 for non GDML related work )

If you get an error message No module named 'lxml' then on Linux you can diagnose as follows.

To check path FreeCAD uses from a command line.

freecad -c
import sys
print(sys.path)

To check lxml correctly installed for freecad

freecad -c
import lxml
from lxml import etree
print(etree.LXML_VERSION)

On linux to install lxml to a specific directory

pip3 install lxml -t <directory>

For more information on GDML see

GDML User Guide

GDML Solids

GDML Solids are implemented as FreeCAD Python Objects and have the same properties as defined by GDML. By selecting an Object the properties can be changed via the FreeCAD properties windows and the resulting changes displayed.

1. Start FreeCAD
2. Select the GDML workbench from the workbench dropdown menu.
3. Select File > New
   Result: This will load the default GDML File with materials and creates a World Volume.
4. Create 1-n Volumes in the World Volume by
   • Click on the Part icon (image: yellow blockish icon)
   • Drag the created Part to the World Volume in the Tree window
   • Part maybe renamed via right click context menu
5. Create GDML Solids by:
   • Clicking on the corresponding icon of the workbench.
   • Drag the GDML object to the appropriate Part again via the Tree window
   • You can then change the attributes by selecting the GDMLObject in the Tree window then changing the properties in the Property View

So a valid structure for a GDML file is:

• Single World Volume (Part)
• A number of Volumes (Parts) under the World Volume
• A number of GDML Objects can exist in one Part ( GDML Logical Volume)

6. To Export to GDML
   1. Select the 'World' Volume ( Default Name WorldVol )
   2. File export
   3. Select filetype as GDML ( Bottom Box of Export file window)
   4. Select Destination and file name with GDML as file extension

Important Notes:

• Opening a new file when the GDML workbench is active will load a Default file.
• The Default file is defined in GDML/Mod/Resources/Default.gdml.
• If a material is selected in 'Labels & Attributes window at the time a new GDML objects is created then this will set the material of the new Object. If no material is selected the objects material is set to the first material in the Defaults file i.e. SSteel0x56070ee87d10

Upon switching to the GDML workbench, one will notice a number of icons that become available on the Workbench bar.

• Clicking on one the icons will create a GDML object.

  If at the time a material is selected e.g. in the 'Labels & Attributes' window, then the object will be created with that material, otherwise the material will be set to the first material in the list.

• It should then be dragged to the appropriate Part (GDML Logical Volume)

• In neccessary, once can then edit the properties via the properties window. The parameters should be the same as in the GDML user guide.

• If the Object is part of a Boolean you will have to use the recompute facility of FreeCAD to see the change to the Boolean. This can be achieved through the right clicking on the context menu or clicking the Recompute icon in the toolbar.

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Given a lot more solids are supported for import, it is not too difficult to add more, so if you feel you need a particular solid to be added please contact me.

The following icons are available for Tessellated operations

If the selected FreeCAD object has a Shape then a GDML Tesselated Object is created by using the Meshing Workbench default options. If a material is also selected this will determine the GDML material of the created GDML Tessellated Object

If the selected FreeCAD object is a mesh then a GDML Tessellated Object is created. Again if a material is also selected then this will set the GDML material of the GDML Tessellated Object.

1. FreeCAD Supports a large number of mesh file formats including stl, ply, etc so Mesh 2 Tessellate allows these to be converted to a GDML Tessellate object

2. The Mesh Workbench offers a range of meshing facilites with options ( Meshes | create mesh from Shape )

   • Standard
   • Mefisto
   • Netgen

   So having created a mesh using the Mesh workbench, one can then switch to the GDML Workbench to create GDML Tessellated objects from these.

A lot more GDML solids are supported for import. For example all Solids used by the CERN Alice.gdml are defined.

On import or open of a GDML file a Dialog box will open with two options

• Import
• Scan Vol

Import will do a straight import of GDML Objects.

Scan Vol is for large files like Alice.GDML that take far too long to process.

Volumes are only processed to a limit depth i.e. volume names are determined but not processed For unprocessed volume the names are preceded by NOT_Expanded so an example volume name would be: NOT_Expanded_<VolumeName>

Unexpanded Volumes can be expanded by:

1. Switching to the GDML workbench.
2. Selecting a volume in the labels & attributes window
3. Clicking on the experimental Expand Volume icon 'E'

On opening of a GDML file the appropriate FreeCAD implemented python Object is created for each solid

The first icon on the workbench bar is different. If you select a object by one of the following methods

1. A volume via the Combo view - Model - Labels & Attributes.

   Then click on the icon it will cycle the display mode of the selected Volume and all its children. The cycle is Solid -> WireFrame -> Not Displayed -> Solid

2. In the main display - select a face by

   Then click on the icon it will cycle the display mode of the selected object

SampleFiles directory contains some sample gdml files.

One in particular is lhcbvelo.gdml. This file takes a LONG LONG time to import/open, over a minute on my system, but does eventually load. On my system I have to okay one wait. When it finally does display you will want to zoom in.

If when it is displayed you go down the Volumes tree to VelovVelo under the World volume then click on the toggle icon ( 1st GDML icon in the workbench) Again wait patiently and the display will change to wireframe. You can then decend further down the Volumes tree, select one and again use the toggle icon and that volume and children will change to Solid. In this way various parts in different volumes can be examined.

To export to GDML

1. Select the 'world' Volume, should be first Part in Design
2. File export
3. Select GDML as filetype
4. Make sure file has GDML as file extension

GDMLObjects are output as straight GDML solids

The following FreeCAD objects are output as GDML equivalents

If not handled as above then objects shapes are checked to see if planar, if yes converts to Tessellated Solid with 3 or 4 vertex as appropriate. If not creates a mesh and then a Tessellated solid with 3 vertex.

Standard FreeCAD export facilities are available which includes the ability to create a STEP version

If you select the Materials Group in Tree view and then use the standard FreeCAD export, the export will create an xml file of the material definitions. You can then import this file and the material definitions into a separate FreeCAD document. Note: The file extension used should be xml NOT gdml

The Materials directory contains a number of Materials XML files including NIST Database that can be imported.

Importing a GDML will create FreeCAD objects for the above and export should create the same GDML definitions as imported.

The Ability to change to change these maybe implemented in the future.

There is now an option to toggle Printverbose flag to reduce printing to the python console.

• Select a volume/Part i.e. the first Part which is the GDML world volume and click on the compound icon 'C'

  1. Creates an object named Compound under the selected Volume
  2. Create an FEM Analysis Object.
  3. All the materials of the objects in the Volume/Part/Compound are added to the Analysis Object.

• You can then switch to the FEM Workbench (Finite Element Analysis) and proceed with an analysis which would include:

  1. Double click on each of the materials to edit their properties
  2. From the FEM workbench select the Compound Object and click on the icon to create a Mesh.
  3. Rest would depend on what analysis and what solver it is intended to use.

  Also as an experiment: thermal parameters have been added to the GDMLmaterial object so these could be changed before creating a compound. One option to be would be to add elements to GDML files to enable loading and exporting, but then they would NOT be standard GDML files (maybe a different file extension?)

In directory Utils You will find a python script gdml2step.py for creating a step file from a gdml file.

syntax is

     python3 gdml2step.py <input gdml file> <output step file>
     
     The step file should be given a .step extension.
     
     In theory other file extension should produce a file of the appropriate type,
     e.g. iges, but this is untested.

• Change structure of xml handing to use Python class rather than global variables
• Check handling of different Positioning between GDML & FreeCAD
• Add support for quantity
• Add further GDML Objects
• Add facility to edit Materials
• Add facility to edit Isotopes
• Add facility to edit Elements
• Documentation
• Investigate handling of Materials
• Need to sort out AIR definition

Workbench

• Workbench Dialog for initial GDML Object values(?)
• Analyze FreeCAD file for direct conversion of object to GDML solid
• Display mesh for objects that will not directly convert
• Provide options to control meshing objects that will be Tessellated
• Icons to Analize and Export

Note: For NIST Materials database see http://physics.nist.gov/PhysRefData

based on gdml.xsd

• 'Volumes'

  • Must have solid & material ref

• PhysVol

  • Must contain volref ( or file )
  • volref must not be same as current volume name
  • May contain position or position ref
  • May contain rotation or rotation ref

Developers

• Keith Sloan
• Damian Lambert

Graphic Icons

• GDML Shapes designed by Jim Austin (jmaustpc)
• Cycle icon by Flaticon see www.flaticon.com

Thank you also to:

• Louis Helary

• Emmanuel Delage

• Wouter Deconnick

• Hilden Timo

• Atanu Quant

• FreeCAD forum members (Applogies if I left anybody off ) :

  • wmayer
  • Joel_graff
  • chrisb
  • DeepSOIC
  • ickby
  • looooo
  • easyw-fc
  • bernd
  • vocx
  • sgrogan
  • onekk (Carlo D)

• OpenCascade Forum members:

  • Sergey Slyadnev

• Workbench Dialog for initial GDML Object values(?)

• Handle different Positioning between GDML & FreeCAD

• Add support for quantity

• Add further GDML Objects

• Add facility to add Volume

• Add facility to edit Materials

• Add facility to edit Isotopes

• Add facility to edit Elements

• Workbench

  • Analize FreeCAD file for direct conversion of object to GDML solid
  • Display mesh for objects that will not directly convert
  • Provide options to control meshing objects that will be Tessellated
  • Icons to Analize and Export

• Tidy softLink script

• Make FreeCAD an installable workbench

• Documentation

• Investigate handling of Materials

Please report bugs by opening a ticket in the FreeCAD_Python_GDML issue queue

Note: I am always on the look out for test gdml files (small to medium size)XXXX# FreeCAD_Python_GDML

To contact the author via email: keith[at]sloan-home[dot]co[dot]uk