A BIM model evolves throughout the lifecycle of a project as more detailed design and digital information is added. It can start as the deliverable from a laser scan or Scan to BIM survey and is normally prepared in Revit software and issued in a .rvt file format, although exports can be made to other file formats where needed.
The elements represented in a 3D BIM model are usually specified using a LoD (Level of Detail or Level of Development) which ranges from 1 to 5.
LoD1 is a basic block form that lacks any real detail and is used for massing purposes, through to a
LoD5 which contains a high level of content and detail and is used for as-built record purposes and facilities management.
Generally, a measured building survey model is developed to a LoD 3 ‘architectural’ specification, but this can include some elements that normally only appear in a LoD 4 model.