LOD vs LOA: a plain-English explainer

Two specs get mixed up all the time.

LOD: Level of Development

From the BIMForum LOD Specification. It describes how far the information in a model element can be relied on, from LOD 100 (a placeholder) through 200, 300, 350 and 400 to 500 (field verified). It is about how developed and reliable the element is, not how pretty it looks.

LOA: Level of Accuracy

From the USIBD Level of Accuracy Specification. It describes how accurately something was measured or is represented, as ranges at 95% confidence:

• LOA10: worse than 5 cm
• LOA20: 15 mm to 5 cm
• LOA30: 5 mm to 15 mm
• LOA40: 1 mm to 5 mm
• LOA50: 0 to 1 mm

The spec separates measured accuracy (the scan or survey) from represented accuracy (the model). A model can never be more accurate than the data it was built from.

Why it matters for scan-to-BIM

A brief that says "LOD 300" alone doesn't say how close to the scan the model must be. Ask for both: an LOD per element category and an LOA for measured and represented accuracy, and agree how it will be checked.

Corrections and examples from your own projects are very welcome.