diff --git a/doc/sphinx/source/design-notes.rst b/doc/sphinx/source/design-notes.rst
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--- a/doc/sphinx/source/design-notes.rst
+++ b/doc/sphinx/source/design-notes.rst
@@ -7,7 +7,7 @@
 ==============
 
 G-Code Parser
--------------
+=============
 
 The RS-274 parser is generated automatically from the grammar defined in the paper |NIST-RS-274|_
 (Appendix E) using the generator `PLY <https://www.dabeaz.com/ply/ply.html>`_ which implement a
@@ -19,6 +19,92 @@ The parser construct an `abstract syntax tree (AST)
 User can subclass this parser to support a derived G-code flavour.
 
 G-code flavours
----------------
+===============
 
 The different flavours are partly handled in |YAML|_ files.
+
+
+G-code Generation and Simulation
+================================
+
+Computational Geometry Engine
+=============================
+
+The computational geometry engine requires these features :
+
+* import standard 2D object file, e.g. SVG and DXF
+* import standard 3D object file, e.g. STL
+* 2D path erosion and dilation, e.g. to compute cutter radius compensation
+* 2D/3D Minkowski sum along a path
+* 3D extrusion
+* 3D Boolean operation : object - tool path
+
+List of the Main Open Source Computational Geometry Algorithms Libraries
+------------------------------------------------------------------------
+
+The Computational Geometry Algorithms Library
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+`CGAL <https://www.cgal.org>`_ is a software project that provides easy access to efficient and
+reliable geometric algorithms in the form of a C++ library. CGAL is used in various areas needing
+geometric computation, such as geographic information systems, computer aided design, molecular
+biology, medical imaging, computer graphics, and robotics.
+
+CGAL is used in:
+
+* many academic projects
+* `OpenSCAD <http://www.openscad.org>`_
+
+Git repository and Python binding:
+
+* https://github.com/CGAL/cgal
+* https://github.com/CGAL/cgal-swig-bindings
+* https://github.com/sciencectn/cgal-bindings
+
+STL (STereoLithography) format support:
+
+* https://en.wikipedia.org/wiki/STL_(file_format)
+* https://doc.cgal.org/latest/Polyhedron/classCGAL_1_1Polyhedron__incremental__builder__3.html
+
+  * include/CGAL/IO/Polyhedron_builder_from_STL.h
+
+* https://github.com/CGAL/cgal/blob/master/Polyhedron/demo/Polyhedron/Plugins/IO/STL_io_plugin.cpp
+
+  * demo/Polyhedron/Plugins/IO/STL_io_plugin.cpp
+
+* https://github.com/CGAL/cgal/blob/master/Polyhedron_IO/include/CGAL/IO/STL_reader.h
+
+  * include/CGAL/IO/STL_reader.h
+  * include/CGAL/IO/STL_writer.h
+
+Open CASCADE
+~~~~~~~~~~~~
+
+* https://www.opencascade.com
+* `Open CASCADE Community Edition <https://github.com/tpaviot/oce>`_
+* https://github.com/tpaviot/pythonocc-core — python wrapper
+
+Open CASCADE is used in:
+
+* `Salome <http://www.salome-platform.org>`_
+* `FreeCAD <https://freecadweb.org>`_
+.. `code_aster <https://www.code-aster.org>`_
+
+
+G-code Visualisation
+====================
+
+The open source `Qt <https://www.qt.io>`_ framework provide a multi-platform User Interface framework with 3D support.
+
+* `Qt 3D <https://doc.qt.io/qt-5/qt3d-index.html>`_
+
+  Qt 3D provides functionality for near-realtime simulation systems with support for 2D and 3D rendering in both Qt C++ and Qt Quick applications.
+
+* `QMesh Class <https://doc.qt.io/qt-5/qt3drender-qmesh.html>`_
+
+  QMesh supports the following formats:
+
+  * Wavefront OBJ
+  * Stanford Triangle Format PLY
+  * STL (STereoLithography)
+  * Autodesk FBX if the SDK is installed