Design vs as-built comparison
Comparing the design or BIM model with a laser scan point cloud: colour deviation maps, deviation reports and construction quality control.
A design versus as-built comparison checks the real geometry of a completed or ongoing structure by overlaying it on the design drawings or the BIM model. The actual condition is captured as a point cloud by 3D laser scanning; the distance of every point from the design surface is then calculated and the result is shown on a colour deviation map.
This check gives owners, technical supervisors and contractors an objective basis for decisions. It reveals the out-of-plumb of columns and walls, slab flatness and level differences, the position of openings, and the installation accuracy of steel structures and pipework. When problems are found early, costly demolition and rework at later stages can be avoided.
Work starts by agreeing the design data (Revit, IFC, DWG or Civil 3D model) and the allowable tolerances. The structure is scanned with a terrestrial laser scanner, the point cloud is tied to the survey control network and aligned with the design model in the same coordinate system. The comparison is performed in specialised software, and deviations are analysed by element, floor or zone.
The deliverables are a report highlighting areas outside tolerance, colour maps and sections. Where required, the comparison is repeated at different construction stages, or an as-built BIM model is produced from the results.
When you need it
- Compliance of construction with the design must be verified
- Installation accuracy of structures needs to be controlled
- Deviations must be found before the next construction stage
- An objective document is needed for handover and acceptance
- Disputes with a contractor must be resolved on the basis of measurements
What's included
- Review of design data and tolerances
- 3D laser scanning of the structure
- Tying the point cloud to survey control
- Aligning the cloud with the design model
- Colour deviation maps
- Deviation analysis by element and zone
- Report and sections
How we work
- Agreeing the design model and tolerances
- On-site scanning and georeferencing
- Cloud processing and alignment with the model
- Comparison and deviation analysis
- Report delivery and walkthrough of results
Deliverables
- Colour deviation maps (PDF, images)
- Technical deviation report
- Sections of problem areas (DWG, PDF)
- Point cloud (RCP, E57)
