LEVEL OF DETAIL (LOD) IN BIM MODELS
The aim of this article is to explain what the meaning of Level of Detail (LOD) is in the BIM environment in order to clarify the confusion that exists about this concept.
To start, LOD defines the graphical content of a BIM model. A lower level of detail means 2D graphical content or 3D conceptual massing of a building, whereas a higher LOD means specific modelling of the architectural and constructive elements of a building, maybe in more or less detail. So in other words, the LOD increases as the project goes through stages from inception to completion.
LOD CLARIFIED
There are a few acronyms that need to be defined in order to gain clarity and they are LOMD, LOI and LOD.
LOMD stands for Level of Model Definition. It is the sum of LOD and LOI that creates LOMD.
LOD stands for Level of Detail. LOD refers to the graphical aspect of a 3D BIM model (might include 2D elements). So in other words it is the volume and geometry of the building. It is what you can visually see.
LOI stands for Level of Information. It is all the information that the different elements contain. Examples can be information as basic as a door/column tagged as a door/ column respectively with the use of uniclass codes or it can be technically more advanced. An example of the latter would be a fire protection of the door or the type of steel or concrete the column is made of. Another example is that the price of these elements.
And in order to acknowledge this information there is a need to interrogate the model. This can be done by clicking the element so a window will prompt showing this information. One can also export a report if required, but this will all depend on the software that is being used.
Furthermore, one must understand that LOD and LOI are not necessary in the same level of development. One can have in any element of the model a high LOD and a low LOI, but totally unusual, a low LOD and high LOI, again, depending on the project needs.
So the LOD of different elements of a BIM model may increase at different rates. More than often the designers, consultants and/or other members of the project may progress at a different pace depending of the needs of their specific disciplines. In order to keep the development of the project consistent it is up to the employer defining the LOD required at any stage of the project for every discipline, the employer defines the LOD in the document called “Employer’s Information Requirements” (EIR).
Examples of LOD
LOD1
MBS 2D Drawings
LOD2
TOPOGHAPHY LOD2
-3D mesh only.
NEIGHBOURING BUILDINGS. LOD2
-External, conceptual massing, without openings. Unless specific request.
LOD3
INTERNAL MODEL LOD3
-Internals: Doors, 1 family with standard sizes, ornament, cornicing, skirting and crowns not to be modelled, no furniture or sanitary fixtures to be modelled, railings not to be modelled. Unless specific request.
EXTERNAL MODEL LOD3
-Elevations and roofs: No ornaments to be included, simplified frame geometry for windows and doors, simplified geometry on cornices, no services to be modelled. Unless specific request.
LOD4
INTERNAL MODEL LOD4
-Internals: Doors, panel detail included, ornament, cornicing, skirting and crowns to be modelled, furniture or sanitary fixtures to be modelled with elements from ArchiCad library only, railings in detail to be modelled.
-Elevations: Ornaments to be included, with some simplification on organic geometry, window and door detail included, cornices and railings detail included. Services to be modelled.
The United Kingdom has different regulations to other countries and the LOD is defined at different stages. Firstly, it is the customer who defines LOD0 or LOD1 for first stages and LOD4 up to LOD5 for the final stages. At Scope Surveys, as a proposal (since employers define LOD) is what we work with these LOD´s.
If you wish to discuss this with the CAD specialists please feel free to contact us on info@scopesurveys.co.uk or 02087713477
