Every scan-to-BIM quote meets the same question sooner or later: how detailed, and how accurate? The answer is two different measures, and mixing them up is a common source of disputes. This article explains LOD vs LOA, how they work together, and how to write them into a scope your client understands.

LOD vs LOA in one sentence each

• LOD (Level of Development) describes what is modeled and how much information it carries: a generic wall, a wall with its real layers, or a wall with every opening detail.
• LOA (Level of Accuracy) describes how close the model or the measurement is to the real building, as a tolerance range.

A model can be very detailed but inaccurate, or very simple but accurate. That is why a scope needs both.

What LOD means

LOD is most often defined with the BIMForum Level of Development Specification. In short:

• LOD 100: a symbol or mass, no real geometry.
• LOD 200: generic elements with approximate size and position.
• LOD 300: elements with specific size, shape, position and orientation.
• LOD 350: LOD 300 plus the interfaces with other elements.
• LOD 400: enough detail for fabrication.

For existing buildings, most scan-to-BIM projects deliver LOD 200 to 300 for architecture and structure. MEP is often lower because many systems are hidden in walls and ceilings and cannot be scanned.

What LOA means

LOA is defined in the USIBD Level of Accuracy Specification. It gives tolerance bands, usually stated at a 95% confidence level:

The specification also separates measured accuracy (how good the scan data is) from represented accuracy (how close the model is to that data). A scanner can measure to a few millimetres, but a modeler who draws a perfectly straight wall over a wall that leans 20 mm still delivers LOA20 for that element.

How LOD and LOA work together

Think of a table where each element group gets both values:

• Exterior walls: LOD 300, LOA20
• Floors and slabs: LOD 300, LOA20
• Structural columns and beams: LOD 300, LOA30
• Doors and windows: LOD 200, LOA20
• Visible MEP over a set diameter: LOD 200, LOA10

This is far clearer than "LOD 300 model", which says nothing about tolerance, and it shows the client where the cost goes: tighter LOA means more time per element.

Write it into the scope

A short scope section prevents most arguments at handover:

1. Element table with LOD and LOA per group, as above.
2. Modeling rules for real-world imperfections: are walls modeled straight and plumb, or do they follow the scan? Are floors flat or do they follow the measured slope?
3. What is excluded: hidden services, furniture, elements below a minimum size.
4. How accuracy is checked: which areas are checked, against which data, and how the result is reported.

Check the model against the scan

LOA is only meaningful if you can show it. Before delivery, compare the model with the point cloud and keep the result as part of the handover. Deviation Check colors every scan point by its distance to the model and lists the elements outside your tolerance, so you can fix them before the client finds them.

For surfaces that are not flat, such as uneven slabs and terrain, measuring points directly from the scan keeps the represented accuracy high: see Floor By Points and Topo By Points.

Next steps

Clear LOD and LOA make quoting and checking easier. Read the full scan to BIM workflow in Revit, or keep your delivered model tidy with practical Revit naming conventions.

Get ZetaBIM

ZetaBIM is a Revit plugin for scan-to-BIM teams. See the complete guide to the Revit point cloud plugin workflow. Download ZetaBIM to try it, browse more ZetaBIM tutorials, or watch the videos on the ZetaBIM YouTube channel.