Pictures above are not mine. Sources of them:
- LeoCAD: https://www.leocad.org
- FreeCAD: https://community.osarch.org/discussion/474/floss-workflow-with-regard3d-blender-freecad
- BRL-CAD: https://brlcad.org/gallery/picture.php?/105/category/12
Sharing is very appreciated.