How is a GR CATEGORY different from an LOD level?
The four “graphical representation” categories GR1 to GR4 indicate how detailed the geometry of a BIM object needs to be in order to meet the current needs of a BIM actor. GR categories are a key part of the lean set-of-information (SOI) approach to BIM data management.
As a property of a BIM element or assembly, a GR code denotes the level of detailing in that building component’s 3D model. But unlike an LOD level, a GR category ties a BIM object’s level of detailing to its intended use. That lets actors request, create and get just the right amount of detail every time. It also helps to avoid accumulating unnecessary information in models, especially for ready-to-use items and assemblies.