Generating LOD-1 representation of buildings using CGAL

[DorianG02]

Internship on generating LOD-1 representation of buildings using CGAL

• Intern : Dorian Geraldes Pereira @DorianG02 (Master 1 CSMI - https://csmi.cemosis.fr)
• Advisors : @vincentchabannes and @palliez

Overview

This project is part of the ExaMA and Hidalgo2 initiative, where Cemosis aims to implement new tools to improve Urban Energy Simulation. Our work focuses on generating 3D models of buildings. The goal of this internship is to develop a geometric reconstruction tool for LOD1 buildings. This level considers buildings as collections of polygons extruded by height, with specifications for roof shapes. Based on this information, we aim to reconstruct a 3D mesh that adheres to geometric conformity constraints.

The key objectives include:

• Generation of a surface mesh representing the building's external envelope.
• Addition of internal walls delimiting exterior walls and any slabs for each floor.
• Roof modeling.
• Creation of a 3D building volume mesh (structure and/or indoor air).
• Mesh adaptation: quality control of the produced meshes.
• Combining different parts of a building to accurately represent more complex shapes.

What has already been done

• Generation of a surface mesh representing the building's external envelope for one simple Polygon
• Addition of internal walls delimiting exterior walls (no markers yet) and any slabs for each floor (Generating Floor of the same shape as the input Polygon)
• Roof modeling based on the input Polygon ( one shape possible but can be a little bit modified )
• The building and roof is combined but result is not guaranteed for more complex and multiple polygon

Tools

• Polygon Mesh Processing from CGAL (Used to create surface mesh )
• 2D Straight Skeleton and Polygon Offsetting from CGAL (Used to create roof)
• 3D Mesh Generation From CGAL ( Used to mesh volume )

Current issue

• Convert Mesh to Polyhedron To perform 3D Meshing
• Mesh the air inside the building in addition to the structure

Initial Data

Currently the data used is a simple polygone defined like this :

8
0 0 0
0 4 0
-4 4 0
-4 8 0
4 8 0
4 4 0
8 4 0
8 0 0

but in the end we want to create building more complex and with multiple polygon using GIS data

Current result

The current result is the surface mesh with internal wall and roof, multiple floor can be added .
Using this result and converting it to an off format to use it on 3D Mesh generation (not an automatic conversion) has resulted in a 3D Mesh of the structure of the building (The air inside is not meshed for now)

            Surface Mesh                                Zoom Surface Mesh                3D Mesh with 4 floors

References

• CGAL, Computational Geometry Algorithms Library, https://www.cgal.org/
• https://ktirio.fr/