LOD acronym means Level of Development. LOD is the level of analytic progression of the informative models. LOD communicates the grade of reliability of the information included in a BIM model.
While in a standard approach, moving from sketches to detailed design gives a clear definition of the project stage itself, in a BIM model borders between what is defined and what is not are much more shaded.
Since graphical data are only a part of the information carried by a BIM model, it is possible to have a 3D model containing information which is not related to its geometry at all: cost, manufacturer, model, weight, power, time. The model gathers both geometric and non-geometric information. That’s why we need a standard called LOD that clarifies for each stage which information shall be defined or not.
LOD, as acronym of Level of Detail, was invented by Vicosoftware, as a reference to communicate the grade of reliability of cost definition. The American Institute of Architects (AIA) adopted this concept, applied it to all the uses related to BIM and changed the meaning to Level of Development.
Changing only the last word from “Detail” to “Development” means that the new LOD embodies the grade of reliability of the information, not the overall quantity of information.
There are different standards to define LODs: AIA’s standard is one of the most famous LOD and it uses a numeric scale from LOD 500 (which contains all the information needed for an “As-built” project) to LOD 100 (which contains the information needed for a preliminary design stage).
UK LOD definition clarifies that LOD is defined in part by geometric information (in UK also called LOD = Level of Detail) and in part by non-geometric information (in UK called LOI = Level of Information).
Whatever standard has been chosen, since every project is unique, a specific LOD definition is needed for each phase, for each category of elements. Once LOD is defined for each category all the specialists are in charge of defining which information is required in the definition of the BIM model and which is not.