BIM and Surveying
Integration of survey data with BIM models. El-Eman Office provides BIM-compatible survey data for modern construction.
From point cloud to model
When BIM and surveying are discussed, the most prominent application is turning laser scanning data into a model. The scanner captures millions of points representing the building's surfaces, and these are merged from several positions into one cloud. The engineer then models elements such as walls, columns, ceilings and openings on top of the cloud. Model accuracy varies with purpose: a model for architectural design differs from one for facility management. The level of detail required for each element should be agreed beforehand to avoid excess or shortfall.
Control points and shared coordinates
Disciplines collaborate in a BIM environment within one model, which requires a unified coordinate system. If an architectural model is created with a different origin from the structural model, the two will not align. The surveyor defines the survey base point, the project base point and the direction of north, and ties them to the official coordinates. He also provides fixed control points used later to set out elements and verify construction.
- Define units and coordinates in a BIM execution plan before starting.
- Document the control points on site with protected markers.
- Tie the different models to the same base point.
Verifying construction against the model
After construction, a laser scan is carried out and the point cloud is compared with the design model, with deviations shown in colour, such as a raised slab, a leaning column or a shifted opening. This comparison helps find problems early, before finishes are installed, and confirms that prefabricated elements such as facades and steel structures fit their positions. In the end the updated model becomes an as-built model that the owner uses for operation, maintenance and extension.
- Define the goals for using the model and the detail required.
- Set up control points and a unified coordinate system.
- Collect survey data and produce the model to the agreed accuracy.
- Compare what is built with the model periodically and update the final model.
Challenges of applying BIM in local projects
Projects face challenges including a shortage of trained staff, different software and file formats, unclear requirements in contracts, and the need for powerful computing. It is wise to start with a pilot project or part of one, with clear goals such as clash detection or quantity extraction, rather than applying BIM everywhere at once. It also helps to agree at the start on exchange formats and each team's responsibilities for the model, so efforts are not duplicated and information is not lost between disciplines.
Frequently asked questions
Does every project need BIM?
No. The benefit grows on complex, large or multi-discipline projects, while small projects may be fine with traditional drawing.
What is the difference between a point cloud and a model?
A point cloud is raw measurement with no meaning attached to the elements, while a model defines the elements, adds information to them and allows quantities to be extracted.
Does BIM guarantee a project free of clashes?
It reveals early clashes between disciplines, but the result depends on the quality of the models and coordination between teams.
