How to check a Scan to BIM model against the point cloud

Check three things, in order

1. The scan: is the point cloud itself accurate and complete?
2. The geometry: does the model match the point cloud within the agreed tolerance?
3. The information: is the model built to your standards and usable in your tools?

1. Check the scan

• Registration report. Look at errors between scans and against survey control. Large or uneven errors show up later as doubled or skewed walls.
• Control check. Compare a few independently surveyed points with the cloud.
• Coverage. Walk through the cloud. Note shadows, missing ceiling voids and inaccessible rooms.
• Noise. Check that people, vehicles and reflections were cleaned out.

The model can never be more accurate than this data. See choosing a scanner for typical accuracy by device.

2. Run a deviation analysis

A deviation analysis measures the distance from every point to the nearest modeled surface and colours the result. Tools include ClearEdge3D Verity, Leica Cyclone 3DR, FARO software, Navisworks and the open-source CloudCompare, which can compute cloud-to-mesh distances after exporting the model as a mesh.

• Compare by element category so results map to the LOA in the specification (see how to write a Scan to BIM specification).
• Look at the distribution, not just the average: the USIBD LOA bands are stated at 95% confidence.
• Investigate clusters of large deviation. They usually mean a misplaced element, a missed object or a registration problem.
• Remember that points on things not modeled (furniture, clutter) will show large deviations. Filter them out.

3. Spot-check critical dimensions

Measure a handful of dimensions that matter to the design in both the cloud and the model: floor-to-floor heights, structural grid spacing, opening widths, clearances in plant rooms, pipe centrelines at connection points.

4. Check completeness

• Every area and discipline in scope is modeled.
• Inferred geometry (hidden behind finishes or out of view) is flagged, for example with a parameter or workset.
• Objects that should be separate elements are not merged.

5. Check modeling standards

• Correct categories: walls as walls, not generic models; pipes as pipes.
• Levels, grids and phases as specified; existing elements on an "Existing" phase if required.
• Naming, worksets and parameters as in your template.
• Coordinates match the survey control or project base point.
• LOD per discipline as specified (see LOD levels explained).

6. Check the IFC

Open the IFC in an independent viewer and check that entity types, property sets and spatial structure came through the export. If your organisation defines requirements formally, buildingSMART's Information Delivery Specification (IDS) lets you check an IFC automatically. See IFC or Revit?.

Acceptance checklist

Apply the same checklist to any provider, us included. You can compare scan and model side by side, from the same camera, in our LiDAR samples.

Frequently asked questions