3D display of a façade lighting project

We are convinced that the use of 3D virtual models can facilitate sustainable development approaches, says Souheil Soubra, Head of CSTB's Modelling division.  They form a high performance simulation tool that provides decision makers with the ability to make choices in full knowledge of the facts, by testing different scenarios.  Thus, from now on, they will be able to display the impact of different types of development projects on the quality of life (for example on CO2, emissions, or the sound environment in a district) or represent the energy efficiency of a building.”  Furthermore, these virtual models are easily understandable to all population categories and thus provide support for concertation.

Therefore, CSTB worked in partnership with the Ecole Nationale des Ponts et Chaussées to develop software capable of using digital photographs to create an interactive 3D model.  (Link with the "Imagine: l3D modelling in a new era"? article).

The software is more precise than CAD software and less expensive than laser telemetry, and gives a very high resolution result at very low cost because all that is necessary to obtain a 3D model is to take several photographs of a structure from different viewing angles.  The computer automatically restores the third dimension, in the same way as a brain reconstructs depth from ocular vision.

The technology is now operational continues Souheil Soubra.  We participated in an international benchmark this year, in which our technology obtained the highest ranking.  Note that France has taken the lead in this field at the boundary between fundamental and applied mathematics.”  The partnership developed with the Ecole des Ponts et Chaussées, through which knowledge has been pooled since January 2009 through the creation of a common laboratory, has also boosted developments, particularly in the lighting field.

As far as the stone texture

One of the most useful applications is in the simulation of building façade lighting, in which the quality of rendering is extremely important.  Samuel Carré, CSTB Lighting Engineer, confirms:  “Our model can be used by lighting simulation software, with a better result than can be obtained by other technologies.  Starting from simple digital negatives, or even digitised archived photos, we can use data related to the façade texture (stone grain, colour, dirt, cracks) and restore lighting variations on these elements.”

Overviews of the lighting simulation results applied to the 3D model
Overview of the high resolution 3D model automatically obtained from 25 photographs of the façade

CSTB teams are continuing to improve the model to obtain even more precise data starting from a smaller number of photos, while minimising time necessary for human action.  But Samuel Carré already presented the tool to lighting designers this year.  “We offer them a partial or complete service, from taking pictures to the “photorealistic” illustration of the façade lighting project, possibly including alternate scenarios.  The complete service is completed by physical data presented in the form of tables of values or images coloured by isovalues.”  What pleases most designers?  All information is very accessible and makes presentations to their customers particularly easy.