Before getting into discussion let us define few terminologies in the context:
1. What is BIM? Building information modeling (BIM) is a process of using “information enriched 3Dmodels” throughout the “building life cycle” by leveraging different “tools/technologies”.
2. Building life cycle: Design –Construction – Operations – Refurbishment/Demolition is noted as building lifecycle basically building’s inception to the end.
3. Information in 3D Model: When we say information, it might be
a. Geometric (Visual) Information: representing object's physical shape & size.
b. Non-geometric information: representing the object’s technical properties.
Example 01: Door
· Geometric information: Width of the door, Height of the door, the thickness of the door, its actual color, finish, etc.
· Non-geometric Information: Fire rating of the door, weight, cost code, manufacturer, etc.
Example 02: Air Handling Unit(AHU)
· AHU’s Length, Width, Height, etc are its geometric information.
· AHU’s airflow rate, fan capacity, Coil dewpoint are to be categorized as non-geometric information.
4. Tools/Technologies: While working on the BIM process many software are put into use rather than just one. This is a particularly important understanding as in multiple instances project environment specifies the use of 1 tool for all use cases. Popularly know technologies are illustrated for better understanding.
a. 3D Model Authoring: Revit, Archi CAD, Tekla, Vector works, etc.
b. Collaboration Tools: Navisworks, Solibri, etc
c. Quantification & cost management: Costx, Nova 5D BIM etc
d. Construction Sequencing or 4D: Navisworks, Synchro, etc
e. Operation using CMMS: Granlund manager, Maximo, etc.
LOD: Level of Detail (LOD) popularly refers to the representation of geometric information represented in a 3D model.
Generally, in projects representation is like LOD 100, LOD200, 300, etc LOD 500. Where LOD 100 means the model has lower geometric information compared to LOD 200.
So now that we have understood few terminologies let us get back to our discussion of LOD. In developing an “Information enriched 3DModel” time is spent in 2 activities:
· Developing Geometric Information
· Enriching Non-geometric Information (also referred to as Level of Information need (LOI))
So let us derive an understanding that the time consumed for 3Dmodelling is proportional to the level of detail (geometric & non-geometric) requested in the project.
BIM specification document must clearly specify what is the expected details with reference to geometric information & non-geometric information in the 3D Models (BIM).
Naturally, the question comes what LOD should be specified: Mostly it is the psychology of “Bigger the better”. So, most BIM specification document request for BIM up to LOD 500. But let us put a step back and try to understand what LOD one should specify/request from the design team.