BIM Busters - LOD steadily increases in detail
Read why the idea of a linear increasing LOD during the project is unhelpful and no foundation to order BIM. A BIM myth worth debunking...
Everybody who listened to just one talk about BIM heard about the idea of Level of Development (LOD) and how it gradually increases over the project.
LOD100 is a simple volumetric model for conceptual design.
LOD200 is a more detailed model with elements.
LOD300 has all the details necessary to define a building and do a tender, so it equals an intricate design.
LOD400 additional construction relevant information, like reinforcement steal.
LOD500 The LOD400 model is enriched with the necessary Information for facility management.
The development is clean, linear, and logical, often even seen as equaling the design phases. LOD100 is the conceptual design, and so on. It's logical but wrong and misleading, and as you see in the below picture, there are many visualizations but no clear guidelines.
This goes so far that some clients order a LOD 300 model instead of describing their Level of Information Need (LOIN).
Initially, the LOD was developed to describe the polygons count in computer graphics, and when it was transferred to BIM, without providing a clear definition.
There are several reasons why I believe this idea of linear development is wrong. So it's time to bust a myth:
There are cases when we already want to plan with the exact dimensions and type of equipment in an early design stage. For example, I remember a radiology room where the product information was relevant.
Facility management rarely needs a high level of geometry; it's even counterproductive. In FM, they often need a high level of Information, which is even different from the Information for the construction phase. E.g. guarantee dates, cleaning cycles... I think it makes sense to look at two different deliverables. The documentation of design and construction with all the details from the construction phase. Secondly, the necessary data for facility management.
Design is not a linear but an iterative development. Often, we need analytical models with a lower LOD when necessary for planning.
It does not make sense to model everything in LOD300-500. If there is no need to construct something, we don't need all the construction details in the models. E.g., all the screws in the equipment we buy are already assembled. For cases like that, a low LOD object as a placeholder is enough. The same is true for FM; if the object is not relevant for FM, we don't need all the LOD500 metadata.
Often people talk about the LOD 300 architectural model. It does not make any sense to link LOD on a model level. As any model will contain different information with different LOD. E.g. the window in an architectural model can be a placeholder element with just the right dimensions buy the gypsom bord wall needs all the beams for a proper coordination.
Therefore, we need to think about ways to reduce LOD for specific use cases. For example
For coordination when the production-ready models are too heavy
All kinds of analytical models, e.g., energy simulations and cost calculations.
Working with product models, they are often bloated with unnecessary details, e.g., screws.
I know three different solutions to reduce LOD/LOG:
Manual remodeling. Obviously, this is the most flexible, common and time consuming one.
SimpleBIM can generate a new geometry based on the bounding box. That's great for coordination with lightweight models.
AbstractBIM uplifting low LODs to a LOD200 or downshifting high LODs to the same level. That's great for cost calculation, thermal simulations, and benchmarking projects.
Which one to pick depends on your Level of Information Need (LOIN). This differentiation between LOD and LOIN is one of the relay good aspects of the ISO19650 standard. (In another letter I will probably write about this norm).
I think LOD is a great concept that helps to understand how Information is used, but it's not useful as a way of describing deliverables. There is no clear definition of what needs to be included in a specific LOD! So, it's a great mental model to understand a concept but nothing to use in information requirement documents.
Do you know any other tools that can reduce LOD, please let me know in the comments.
As the client's BIM manager, I tend to leave all these questions to the planners, who have the most experience with their best practice approach. The information that the client needs is set exiplicit project properties My_Pset_Foo and checked against those of the planners, which may lie somewhere, but must be available.
For a long time, endless LOD wallpapers were developed in Germany to show which level of geometric detail was required in which work phase. The first doubts about this approach arose when it became clear that a planner would have to touch the geometry from one work phase to the next. This is exactly where digitalization would have made business processes infinitely more expensive, slower and frustrated planners. Think of a structural engineer who already knows in the design phase exactly how he wants to build the structure in the end.WWeWhichWhich What a waste of time! The logical next step was to separate the geometric data from the information content. LOD = LOG + LOI according to EN 17412, Level of Development = Level of Geomtery + Level of Information.
What we need are geometries and information appropriate to the work phases that are already defined.