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Digital twins · 2026-10-03 · 9 min
Floor Plans, Slab Flatness and Contours From a Point Cloud, in the Browser
Most of what a site team needs from a scan is not a 3D view. It is a plan of what was built, a flatness check before the screed, a terrain with contours, and a clearance that can be quoted. All of them are filters on the same cloud — slices, bands and classes — and none needs desktop software.
Floor Plans, Slab Flatness and Contours From a Point Cloud, in the Browser — IFC Viewer Online article cover
A point cloud of a building site is impressive in 3D and almost useless as it is. Nobody on site needs to orbit forty million points. They need answers to ordinary questions: where were the walls actually built, is this slab flat enough for the screed, how far does the ground fall across the plot, does the duct clear the beam.
Every one of those answers is a filter on the same cloud — a slice, a band, a class — plus a camera in the right place. Applied in the browser, they take seconds.
A horizontal slice about 1.2 m above the floor, seen from above, is a plan of what was built.
Try it: analyse a real scan
A LAS site scan loaded with the pavilion model. In the point cloud panel, the Analyze tab has the floor plan, slab, terrain and vegetation recipes.
Scan and model ready
Six analyses, one cloud
| Analysis | What it does | Needs |
|---|
| Floor plan | Slice 1.2 m above the floor (±0.3 m), top view | Any scan |
| Slab flatness | Band ±8 cm around a picked slab, 1 cm contours | Any scan |
| Terrain | Ground class only, coloured by elevation, contours | Classified scan |
| Remove vegetation | Hide vegetation and low noise | Classified scan |
| Scan vs BIM | Scan in one flat colour over the model | Scan + IFC |
| Clearance | Measure point-to-point on the cloud | Any scan |
A floor plan from a slice
Drawing convention cuts a plan about 1.2 metres above the floor: high enough to catch walls, door and window openings, low enough to pass under most furniture and over skirting. A point cloud cut the same way and seen from above is a plan of the building as built — which is exactly what you need to compare against the design, or to start a survey drawing.
Slab flatness before the screed
Pick a point on the slab, keep only a narrow band around that height, and draw contours every centimetre. A flat slab shows few, widely spaced rings; a slab with a dip or a hump shows tight rings exactly where the problem is. It is a fast visual first pass that tells you where to send the level — not a substitute for a formal tolerance survey, but it often saves one.
Terrain and vegetation: where classes come in
Terrain uses the ASPRS ground class: keep class 2, colour by elevation, draw contours at an interval chosen from the height range. Removing vegetation hides classes 3, 4 and 5 and the low-noise class 7. Both only work on scans that were classified — an unprocessed terrestrial scan has everything in class 0 or 1.
The full class table, and how to tell whether your file is classified at all, is in LAS classification codes explained.
Scan vs BIM and clearance
With the IFC loaded, painting the scan a single strong colour makes deviations obvious: wherever the colour shows through or stands proud of the model, the building differs from the design. When something looks wrong, measure it on the cloud — snap to points, take the distance, and keep the dimension in the screenshot you send.
Aligning a scan with a model in the first place is covered in IFC and point clouds in the browser; tracking progress over time with repeated scans in 4D construction progress from temporal point clouds.
Floor Plans, Slab Flatness and Contours From a Point Cloud, in the Browser