3D Bim

Extract from an article that appeared in the Ingénieur Constructeur n° 536.

In terms of 3D modelling, what are the deliverables and what needs do they meet?

• point cloud surveys give an initial overview of a project’s volumes. It is a data file (x, y, z) that enables you to represent surfaces rather like a photographic negative. It shows the external and internal envelopes of the future structure on which the designers can start projecting, discussing and carrying out simulations. They can also check whether the construction project will come up against any major constraints and, if necessary, they can adapt the project early on. This initial representation and simulation tool is extremely useful in terms of efficiently and quickly fine-tuning the preliminary survey. It can be seen as an intermediate service i.e. the first step towards having a digital model.

• Thanks to its vectorised images, digital models offer “smarter” images. The do the real backbone of the work – neighbouring properties, property boundaries, 3D wall figures, and the application of town planning rules – and give an overview of the preliminary project regulations. Upstream, it allows a more advanced control of all the urban, technical, environmental, regulatory, legal and contractual constraints: simulating occupied surface areas, prospects, setbacks linked to building heights, solar calculations, and checking the absence of easements. It also makes it possible to share all the required data with the client’s various departments (operations, management, legal, etc.) from the start of the project (especially relating to surface areas).

This model is geo-localised enabling overall integration into the urban landscape and interoperability between stakeholders.

What technology do you use to measure dimensions? Do they differ according to the service, point cloud surveys and digital models?

Surveys are the basis of any modelling. To conduct the surveys, we use two techniques depending on whether the premises are occupied or not.

Firstly, 3D laser scanners (or laser scans). These devices scan surfaces in three dimensions and automatically measure the x, y and z dimensions using a large number of points. Their performance is outstanding: they are extremely fast (some can survey a million points per second!) and the readings are accurate to one centimetre and even one millimetre with the latest scanners. However, they have a major drawback – they are cumbersome. Because these devices have to moved when an obstacle blocks the scanning field, they are very difficult to use in occupied premises. Consequently, we tend to use them in unoccupied buildings or ones with large empty spaces.

In certain cases, we enhance the laser scan with photographs that we use to colour the cloud point surveys. We can then export the panoramic images giving our clients an immersive view of the building; we can also add notes. These images are easy to obtain. However, to be usable, they must be computer-processed, which requires a very high computing capacity.

Today, drones are revolutionising image acquisition techniques: a few minutes are enough for a drone to take photographs of a building’s façades. Even though traditional data checks are still required, this technique has significant potential for development.

Other surveying technologies, especially in topography, using cameras, 3D laser scanners and GPS (in vehicles). Digital model files and cloud point surveys can be sent directly to our clients, uploaded to the Cloud or placed on our server. All we have to do is send the client code in order for them to download the data.

Conducting surveys

Preparatory Work

Setting up a main traverse line for the various planimetric and altimetric surveys.

3D Laser Scanner
Lasergrammetry survey of the external envelope of the building and accessible internal spaces using a 3D LEICA Laser Scanner.
Photographs taken with the 3D laser scanner’s integrated camera to:

Processing 3D point cloud surveys

Digital Models

Creating a digital model using Autodesk’s REVIT software.
Modelling structural elements by interpreting 3D point cloud surveys

3D deliverables

Digital models are delivered in .rvt (REVIT) format.
The various elements that make up the digital model are organised into distinct families and are modelled in a generically.