3D object into Geant4, step by step

[Might3D]

How to introduce, import, implement a 3D object into Geant4?

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---------- What you need?
a. Geant4.
b. OpenGL.
c. QT (optional).
d. Visual Studio (or any similar) to compile codes.
e. CMAKE (or similar).
f. Xerces-c (is a must).
g. VulkanSDK libraries (is a must).
h. FreeCAD 1.0.0 RC2 (tried personally and works fine).
i. GDML-workbench (is a must).
j. Load-GDML-color to visualize the .gdml files.

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---------- Procedures:

1. Install Geant4 from its official site: CERN
2. no need for QT unless you want some interactivity with your visualizations. in fact, OpenGL is more than enough to visualize your model. Geant4 itself doesnt need OpenGL to simulate of function, YOU need OpenGL to visualize the model being in simulations.
3. Install QT from its site, get your appropriate license from QT itself. [this step is needed if you are insisting on installing QT].
   Note: be aware of the version, if it’s not compatible it will generate errors while building a solution (with CMAKE, it may generate error if the QT is newer than the mentioned version in the code itself).
   4.Install Visual Studio, make sure it’s the final stable release. Insure you want C++ and Python development kit installed on your PC while installing the packages.
4. Install CMAKE application, this application bakes the codes from the source-into-the-BUILD folder and make a solution that gives the .exe file.
5. Install Xerces-c (or p for python), this library read, import, export the 3D entity.
6. install VulkanSDK.
7. Install FreeCAD from its official site. Install it for everyone, not (only for me) because it generates errors after the installations.
   Note: Keep in mind that FreeCAD data will be installed in %appdata% that’s related to the user’s profile. That’s why you have to choose [for all users] while installation.
8. After installing FreeCAD, goto Tools>AddOns manager>
   Install GDML-workbench, it may ask for updating the LXML and GMSH libraries, say yes.
   You must restart the FreeCAD after installing and addons to take effect.

Note:
You may need to install pip (python) or GitHub Gitbash and similar.
You may need to install some C++ or Python libraries prior to install Geant4 or build the Geant4.

If everything went well, with no errors, it is the time to build your Geant4.

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---------- How to Build the Geant4?

1. Download the official version from its official site.
2. Unrar (or unzip) it in a folder on your PC. I personally prefer to be on a partition different than the C:.
3. Name the unrared Geant4: geant4-SOURCE
4. Create a new folder beside “geant4-SOURCE”, name it: geant4-BUILD.
5. Create other new folder beside “geant4-SOURCE”, name it: geant4-INSTALL.
   Now you have 3 folders:
   1.geant4-SOURCE is for the original files and folders
   2.geant4-BUILD is where you want CMAKE to build your version of Geant4.
   3.geant4-INSTALL is where Visual Studio downloads and install your version of Geant4.

Note: never ever BUILD and INSTALL your version of G4 inside the SOURCE folder. You MUST separate between them.

How to use CMAKE to build the G4 .. it is another discussion.

[Might3D]

-------- How to export 3d object or model or 3d entity from FreeCAD to .gdml file ? STEP by STEP

//------------------ BEFORE proceeding:

1. first, you need to know that FreeCAD is a free 3d application that functions with few helpful commands, like creating primitive geometries and doing some boolean operations for complex shapes, in addition to other materials related stuffs. This application has to install addons and workbenches from 3rd parties. they are all work fine, and very helpfully get you to your purpose.
2. the main use of FreeCAD in this process is to get benefits of its tools with combination of GDML-Workbench (Keith SLoan and Munzer Hindi) that is the ideal tool to export a 3d object into .gdml file.
3. the written .gdml-file after the export process is a special XML file, and can be manipulated and modified using any text-editor.

//------------------ Procedure: Creating 3d object
I am working on thesis on LASER radiations that treat, cure and enhance the ophthalmology. It's pretty dangerous to inspect LASER on real human eye, thus the simulation using Geant4. I need to model an eye in 3ds max that can handle the model in any way you want.

1. model your object using any 3d application ,3ds max, Maya, Blender and so on, these applications are more than enough to model the 3d shape. it CAN BE MODELED with FreeCAD.
   

2. in FreeCAD itself, switch (or activate) the GDML workbench by simply selecting it from the drop down list :
   

3. if you prefer to use 3ds max (or any similar) it's better to use average amount of faces in your model, and if need a very complex model to enter Geant4 it is so recommended that you break your model apart.
   

4. on exporting, select .obj (alias exporter) as the desired format, in this case you MUST tell the 3d application that you need a triangulated faces (not quads nor polygons), otherwise it will generate error in GDML workbench, or simply will never be drawn in it.
   

5. the .obj exporter may contain useful options on export (see the image below). choose the TRIANGULATED faces, otherwise, as mentioned, the object will never draw or it generates error (GDML can not read it)
   

6. summary appears telling you about the number of triangles in the model.
   

7. in FreeCAD (while GDML workbench is still activated), goto Files\import.obj files\select your file

8. choose the second option (it is preferable to do so)
   

9. if for some reason didn't work, redo the import-process and choose the third option, your model MUST show in the viewport.
   

10. read the GDML workbench documentation for HOW-TO-USE.

11. Export your model into .gdml file, simply by Files\export.gdml-file.

12. FreeCAD must tell you: GDML file is written.

13. now in Geant4, GDML example, there is a little way to build an exe file named: load_gdml.exe
    use it to load your file and insure it is working.
    (mine is in: D:\G4-INSTALL\share\Geant4\examples\extended\persistency\gdml\G01\build\Release)
    there are some users on YouTube and GitHub explain in depth how to install and build your G4 and its folders and tools.

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//------------------ KNOWN issues:

1. for some reason, FreeCAD while exporting the file says: (,)
   

Solution:
I think it's a bug in either FreeCAD or GDML workbench, the file must work fine, in somehow it stopps responding and refuses to export any entity ( World, LV, GDML object ... ), it generates the same error and the same messages appears every time: (,)

a. make sure you select the head of all the 3d objects, by default it must be: worldVOL
b. make sure your models are sub-models of this worldVOL
c. try that each model has its own () , and all the objects are SUB-objects of the main header

2. if the message persists to appear
   

Solution:
a. save your work (FC FCStd format) and restart the FreeCAD
b. after saving your work, try to restart the windows, to force FLUSH the memory. it happens, don't worry.

3. after restarting, the export process must go fine now.
   
   

//------------------------------------------------------------------------------------------------------------------------------
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//------------------ Another noticed issue:

1. the exported GDML file may lack of the dummy-object as the GDML-LOAD.exe says.
   i reviewed the GDML codes, it's fine (with comparison to working file), but the error ( no dummy object found) still appear.
   Solution:
   Make sure you have exported the main-header ("worldVOL"), and repeat the steps as in Issue-1 above.

2. for some reason, GDML workbench does NOT assign a material to a selected gdml-obj.

Solution:
Mesh-To-Tess command, it assigns (sets) the material on the new created mesh.

this was my own @Might3D personal experience with GDML workbench, a very big thank-you to Mr @KeithSloan for his help and support.