Guide
How to write a Scan to BIM specification
Most Scan to BIM disputes come from a vague brief. A one-page specification that states scope, LOD, accuracy, coordinates and acceptance criteria prevents almost all of them. Here is what to put in it.
Why the specification matters
"Model the existing building in Revit" can mean a massing model or a fabrication-ready plant room. The price and the turnaround can differ tenfold between those. A clear specification lets you compare quotes like for like (see the Scan to BIM cost guide), and gives both sides an objective way to accept the model.
1. Scope
- Buildings, floors and areas in scope, marked on a plan.
- Disciplines: architecture, structure, MEP, process piping, site, furniture and equipment.
- Exclusions: hidden services, areas without access, small items below a size threshold.
2. Level of Development per discipline
Use the BIMForum LOD Specification terms and set LOD by discipline or element type, not for the whole model. A typical existing-conditions brief:
| Element | Typical LOD | Why |
|---|---|---|
| Walls, floors, roofs, openings | LOD 300 | True size and position for design |
| Structure (columns, beams) | LOD 300 | Coordination and loads |
| Ductwork, pipework, cable trays | LOD 300 to 350 | Clash detection needs connections and clearances |
| Plant and equipment | LOD 300 to 350 | Maintenance access and replacement |
| Furniture and loose items | LOD 200 or excluded | Rarely needed in detail |
See LOD levels explained for what each level means.
3. Level of Accuracy per element
LOD says how developed an element is; LOA says how close it must be to reality. The USIBD LOA Specification defines five levels, which secondary sources summarise as:
| LOA | Range (95% confidence) | Typical use |
|---|---|---|
| LOA10 | Coarser than 5 cm (user defined) | Massing, early planning |
| LOA20 | 5 cm to 15 mm | General existing conditions |
| LOA30 | 15 mm to 5 mm | Most design and coordination work |
| LOA40 | 5 mm to 1 mm | Fit-critical elements, prefabrication |
| LOA50 | Better than 1 mm | Specialist metrology |
State LOA separately for the measured data (the point cloud) and the represented data (the model), and confirm the exact figures against the current USIBD document before using them in a contract. Specifying more accuracy than the use needs adds cost without value.
4. Coordinates and survey control
Say which coordinate system the model must use (project base point, site grid or a national grid), how survey control will be provided, and the units. If the model must align with an existing design model, supply it.
5. Deliverables and standards
- Revit version and template, IFC version (see IFC or Revit?), drawing set if needed.
- Naming, worksets, phases (existing elements on an "Existing" phase), and parameters to populate.
- Whether equipment must be separate elements or may be simplified.
- Registered point cloud format (see point cloud file formats).
- If the model is also for a digital twin or robot simulation, USD with physics properties (see from Scan to BIM to SimReady).
6. QA and acceptance
Require a deviation report of model against point cloud, a list of areas where geometry was inferred, and a short delivery report. Define what happens when an element misses its LOA: correct and reissue within a stated time. How to check a Scan to BIM model has a checklist you can adopt.
Fitting it into ISO 19650
On projects run to ISO 19650, the Scan to BIM specification becomes part of the exchange information requirements for the survey appointment, and the resulting model feeds the asset information model. The UK BIM Framework guidance on developing information requirements is a good reference.
A one-page template
- Project, site address, areas in scope (attach a marked plan).
- Disciplines and LOD per discipline.
- LOA for point cloud and for model, per element type.
- Coordinate system, units and survey control.
- Deliverables: Revit version, IFC version, drawings, cloud format, other formats.
- Modeling standards: naming, phases, worksets, parameters.
- QA: deviation report, inferred-geometry list, acceptance process.
- Programme: scan date, delivery date, review period.
With Moving Atoms, most of this is captured when you upload a scan: you choose the LOD and outputs, add notes, and we confirm the scope before modeling.
Have a scan? Send it to us and get separated, editable Revit and IFC objects back within 48 hours.
Frequently asked questions
What should a Scan to BIM specification include?
Scope, LOD per discipline, LOA per element, coordinate system and survey control, deliverables and modeling standards, and QA and acceptance criteria.
What is the difference between LOD and LOA?
LOD (BIMForum) describes how developed each element is. LOA (USIBD) sets how close measured and modeled geometry must be to reality, as a tolerance at 95% confidence.
What LOA is typical for Scan to BIM?
LOA30, roughly 15 mm to 5 mm at 95% confidence, is common for design and coordination; fit-critical elements may be specified at LOA40.
Sources
- BIMForum, Level of Development (LOD) Specification
- USIBD, Level of Accuracy (LOA) Specification
- Geo Week News, The USIBD's new Level of Accuracy specification
- NavVis, Industry standards are only one piece of the puzzle
- UK BIM Framework, Guidance Part D: Developing information requirements
- CDBB, Asset information requirements guidance