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Currently there are two 3rd party libraries that are necessary for the GDML workbench to function: lxml and gmsh.

lxml is a Python library that processes XML and HTML. Starting with the below versions of FreeCAD, lxml should be auto-bundled as part of the installation:

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

To discover if lxml is installed and accessible by FreeCAD:

1. Open the CLI
2. Invoke the following:

   freecad -c
   import sys
   print(sys.path)

   Result:

Note: To check if lxml is installed correctly:

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

In case there is a need to manually install lxml:

pip3 install lxml -t < directory >

Gmsh is an open source 3D finite element mesh generator. FreeCAD & Gmsh should both be using the same version of OCC (OpenCasCade), the underlying CAD kernel that FreeCAD uses.

At the time of writing a prebuilt version of FreeCAD with OCC 7.6 is not available

Note: The version of OCC with FreeCAD 0.19.2 has a regression with STEP functionality

You can check the version FreeCAD is using with About FreeCAD, copy to clipboard, paste.

To ascertain the Gmsh version, paste the following in to the python console

import gmsh
gmsh.initialize()
print(gmsh.option.getString("General.BuildInfo"))
gmsh.finalize()

It is also possible to run the gmshVer.py script (available in this workbench's Utils directory). To see what versions of Gmsh are available to install, open the CLI and type:

pip install gmsh==

Note: Gmsh must be installed in a location that FreeCAD can access. To check the path FreeCAD uses, open the CLI and type:

freecad -c
import sys
print(sys.path)

In a command window / line

pip install --upgrade --target <Full path to directory> gmsh=='version'

Windows: if no --target option upgrade pip

python -m pip install -U pip

For example on Windows system where FreeCAD is installed on the D drive

pip install --target="D:\FreeCAD 0.19\FreeCAD_0.19\bin\Lib\site-packages" gmsh

will create

D:\FreeCAD 0.19\FreeCAD_0.19\bin\Lib\site-packages\gmsh-4.6.0-py3.8.egg-info
D:\FreeCAD 0.19\FreeCAD_0.19\bin\Lib\site-packages\Lib\site-packages\gmsh-4.6.0-Windows64-sdk

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, this will create a Part(GDML Volume) which contains the GDMLsolid
   • You can then change the attributes by selecting the GDMLObject in the Tree window and changing the properties in the Property View
   • You can alter the position and rotation by changing the Placement parameters in the Part(GDML Volume)
   • You can select and drag the Part(GDML Volume) to the appropriate part of the overall model structure

So a valid structure for a GDML file is:

• Single World Volume (Part)
• A number of Volumes (Parts) under the World 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 of the icons will create a Part(GDMLvolume) containing the 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.

• You can then alter the Objects properties via the properties window. The parameters should be the same as in the GDML user guide.

• Note: If you toggle values via your mouse, you then need to hit enter for the changes to show in the main view.

• 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.

• If a Part(GDML Volume) is selected at the time of clicking on the icon, then the new Part(GDML volume ) and GDML object will be created as a subvolume of the one selected, otherwise the created Part can then be dragged to the appropriate part of model structure

The following icons are available for Tessellated operations

Tessellate

If the selected FreeCAD object has a Shape then a GDML Tessellated 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 has a Shape or Mesh then a Gmsh Panel is displayed in the Task Window.

The panel displays

1. Bounding box information for the selected Object
2. Type of Mesh
3. Input parameters for the Gmsh operation
4. Action 'Mesh' button

Clicking on the 'Mesh' button a GDML_Tessellate_Gmsh Object is created and Mesh info is added to the panel. The input parameters can be changed and another Gmsh operation performed.

Once happy with the Mesh, then Object being meshed can be deleted before exporting to the GDML format. The panel needs to be closed before working on another object

Mesh to GDML Tessellated

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 facilities with options ( Meshes | create mesh from Shape )

   • Standard
   • Mefisto
   • Netgen
   • Gmsh ( Requires FreeCAD 0.19+ )
   • Gmsh also offers a Remesh facility ( Meshes | Refinement )

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

GDML Tessellated to FC Mesh

If the selected FreeCAD object is a GDML Tessellated Object a FreeCAD Mesh is created.

GDML Tetrahedron

If the selected FreeCAD object has a Shape or is a Mesh then a Tetrahedera Object is created by using gmsh. This can then be exported as a GDML Assembly of GDML Tetra

If you would like to see support of remeshing of Tetrahedra the same as Tessellated then please contact me or raise as an issue.

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 one of the the experimental Expand Volume Icons

   • 

   • Expand Selected Volume to Minimum Level

   • 

   • Expand Selected Volume to Full Depth

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 descend 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.

This is still at an early stage of development and has some rough edges, extra support will be added over time

The FreeCAD default settings for Import of a STEP file is to create a single Compound, so the FreeCAD Import/Export Preferences for STEP Import should be set as follows

1. Make sure Import/Export Preferences are set. (Avoid Compound and LinkGroup)
2. Open the STEP File

1. Select FreeCAD-version-number from the Tool bar
2. Then Preference
3. In left hand column select Import/Export

4. Then from top TAB = STEP
5. This displays the Export options followed by the Import Options

1. Switch to the GDML workbench if not the current workbench

2. Click on colourMap Icon ColourMap

3. Allocate Materials to Colours

4. Select Export on the Toolbar

5. Enter directory path ( No file extension )

6. Select the Export type ( Note: Filetype is Not used )

   • Selecting GEMC lower case option GEMC - stp (*.gemc)

     This creates a directory structure for a CAD Factory - Where all FreeCAD Objects with Shapes are exported as stl files

   • Selecting GEMC upper case option GEMC - gdml (*.GEMC)

     Then GDML objects and FreeCAD Object that directly convert are output in a GDML file of a GDML Factory, Other Objects with a Shape are output as STL files in a CAD Factory.

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.

to facilitate preparation for FEM analysis

• 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?)