DEVB TC(W) No. 1/2025
LOD-G as-built verification by point cloud
LOD-G as-built verification checks that the geometry of a BIM model matches the built work, using a georeferenced point cloud. Recent Hong Kong public works contract specifications list as-built point cloud scanning among the model quality checks, next to LOD-G of geometry. Kodifly scans the site, reports each deviation against the model and delivers the files in open formats.
Last updated
- BIM uses
- 3, 14, 15 and 19 in DEVB TC(W) No. 1/2025 Annex 1
- Coordinates
- Hong Kong 1980 Grid
- Point cloud formats
- .las, .rcs and .e57
- Model exchange
- IFC
- Scanner accuracy (Singapore)
- ±2 mm over 10 m, at least 1 million points per second
- Deviation target (Singapore)
- No more than 10 mm
What LOD-G verification means
LOD-G is the Level of Development for graphics. It sets how much geometry each model element carries. LOD-I sets the information it carries. A model can pass every data check and still show a sleeve where none was built.
Recent Hong Kong public works contract specifications make the contractor's BIM quality plan cover model quality (LOD-G), data integrity (LOD-I) and as-built point cloud scanning or field survey for verification. The model compliance check covers grid, survey point, shared coordinates and LOD-G of geometry. A scan answers the geometry question with measurements.
DEVB TC(W) No. 1/2025 Annex 1 sets the BIM uses behind this work. Existing Conditions Modelling (use 3) and As-Built Modelling (use 15) are mandatory. 3D Control and Planning (use 14) requires digital setting-out and construction checking by 3D laser scanners, robotic total stations and similar on projects that require a DWSS, as far as practicable (note m). Asset Management (use 19) requires underground utilities surveys of all opened-up areas, so that a project UU BIM model can go to the maintenance agencies and the Lands Department (note n).
Hong Kong requirements and what Kodifly delivers
| Requirement | Source | Kodifly |
|---|---|---|
| Existing conditions model from 3D digital survey, georeferenced to the Hong Kong 1980 Grid | TC(W) No. 1/2025 Annex 1, use 3 | Delivered: point cloud (.las, .rcs and .e57), build mesh (.tin), ortho-image (.jpeg, .png and .tiff) and H.264 video |
| Digital setting-out and construction checking by 3D laser scanner | Annex 1, use 14 and note m | Delivered: set-out points from the model, then a scan check of the built work |
| As-built point cloud scanning to verify the model | Annex 1, use 15; contract specifications | Delivered: deviation report per element against the model geometry |
| Underground utilities survey of all opened-up areas | Annex 1, use 19 and note n | Delivered: scan of each opened area before backfilling, and the project UU BIM model |
| Tolerances set in millimetres | Contract specifications | Meets: survey-grade terrestrial scanning, ±2 mm over 10 m |
| All tools and software IFC compliant | Contract specifications | Meets: models open from IFC and results return in IFC workflows |
| CIC BIM Standards, DEVB BIM Harmonisation Guidelines, ArchSD BIM Guides, EMSD BIM-AM, Lands Department Building CSU guideline | Contract specifications; TC(W) No. 1/2025 paragraph 19 | Meets: deliverables follow the standards the contract names |
Singapore: LiDAR-based design validation
JTC's Robotic and Automation specification for LiDAR-based design validation asks the contractor to verify any deviation of constructed works against design before backfilling, patching, closing of formwork or boxing-up. The scans cover all M&E underground services, M&E embedded services, and RC wall and beam penetrations. Reports go in progressively, before each area is covered.
What the JTC specification asks for, all delivered
Terrestrial LiDAR scanner
- Accuracy of ±2 mm over a 10 m range
- At least 1 million points per second
- Field of view of at least 300° horizontal and ±90° vertical
- Integrated inertial measurement unit, with GPS as an option for outdoor slabs
Deviation report before cover-up
- Dimensional variance analysis between the scan and the BIM model geometry
- Each deviation identified and measured, against a target of no more than 10 mm
- Quality compliance assessment that highlights areas needing corrective action
- Annotated point-cloud overlays showing where each deviation sits
- Recommended corrective measures for deviations beyond tolerance
How a verification runs
Set control
Tie the scan to the project grid, the Hong Kong 1980 Grid in Hong Kong, so scan and model share coordinates.
Scan before cover
Scan each zone before backfilling, patching, closing formwork or boxing up.
Compare
Lay the point cloud over the model geometry and measure the deviation of each element.
Report and hand over
Issue the report with overlays and corrective measures, and hand over the files.
LOD-G verification, answered
What is LOD-G?
LOD-G is the Level of Development for graphics, the amount of geometry a BIM element carries. LOD-I covers its information. Hong Kong contract specifications check both, and add as-built point cloud scanning or field survey to verify the model.
Which DEVB BIM uses does a scan cover?
Four uses in DEVB TC(W) No. 1/2025 Annex 1. Existing Conditions Modelling (use 3), 3D Control and Planning (use 14, note m), As-Built Modelling (use 15) and Asset Management (use 19, note n), which includes the underground utilities survey.
Is a deviation report the same as design coordination?
No. A deviation is a measured difference between the built work and the model. It is checked on site, after the work is built and before it is covered. Coordination between design models is your BIM consultant's work.
What does JTC require for LiDAR design validation?
A terrestrial scanner with ±2 mm accuracy over 10 m, at least 1 million points per second and a field of view of at least 300° by ±90°. Deviation reports compare the point cloud with the BIM model before cover-up, with a target of no more than 10 mm, annotated overlays and corrective measures.
Who authors the as-built model?
Your BIM team or consultant authors it in your BIM software. Kodifly supplies the survey, the scan checks and the deviation reports that show the model matches the site, and the project UU BIM model from the utilities survey.
Related guides
Check your model against the site
Send us the model and the zones to be covered next. We will show a deviation report on your own work.