BIM Basics: What is LOD?
Updated: Jun 1, 2022
When someone comes to Factory Reality for a scan-to-BIM project, after learning about the end-user and the structure, the next thing we want to understand is the Level of Detail/Level of Development. It is crucial to know the clients desired LOD before starting the model for two reasons:
1) The LOD will directly influence the time it takes to complete the project. Knowing this beforehand will allow you to accurately produce estimates and proposals.
2) The LOD directly relates to how you model, which I will discuss in this post.
Throughout the industry, we see the terms Level of Detail and Level of Development used interchangeably. Often a client will simply express the need for a LOD 200 model, without clarifying if they mean Level of Detail or Level of Development. So what is the difference?
Level of Development
In an article produced by BIMForum (the industry leader in establishing BIM standards, which I will reference throughout this post) the term Level of Development is, “the degree to which the element’s geometry and attached information have been thought through – the degree to which project team members may rely on the information when using the model.”
When thinking of Level of Development think about the accuracy of information. Could someone take the information from the 3D modeled object and use it for real physical applications? Level of Development is critical when working on projects with a lot of Mechanical, Electrical, and Plumbing elements.
Level of Detail
In the world of architectural BIM modeling that we at Factory Reality mostly work in, the Level of Detail is what is most often being referenced. The BIMForum definition is “how much detail is included in the model element.”
The way that I think about Level of Detail, is in terms of describing the element being modeled. How well can you tell what the object in the model is? Is there simply a block representing that an object is there, or can you tell that the object is a chair?
Here’s another way to think of the difference between Level of Detail and Level of Development. A 5-year-old can draw a picture of a car and that picture can’t be used for much more than hanging on their mom’s fridge. The design team at BMW, however, can draw a picture of a car and that picture can be used to develop plans to manufacture a car. That is the Level of Development. Both could be recognized as a car, however, the one by BMW is immensely more accurate and useful. Level of Detail on the other hand is simply asking how much do you want to use your imagination? For example, a kid might play with a basic block and to them, that block could be a table, a chair, a motorcycle, or a car. Watching the kid play, you might not realize what the block is supposed to represent. Versus, giving a kid a Hotwheels car. You would clearly understand that it is a car.
Both Level of Detail and Level of Development is measured using a 100, 200, 300, 400 scale. In this post, however, I will focus on and show examples of Level of Detail 100, 200, and 300. It is important to note that the definitions I give are from BIMForum, and are used to reference both Level of Detail and Level of Development.
The most basic LOD a 3D BIM Model can be completed in is LOD 100. BIMForum says, “LOD 100 elements are not geometric representations…showing the existence of a component but not its shape, size, or precise location” For example you may be able to see that there is an object in the kitchen but are unsure of what exactly it is.
The most commonly used LOD, at least here at Factory Reality is LOD 200. At this LOD the client can see what the object is, but may not need to know the exact characteristics of the object. The BIMForum definition is, “LOD elements are generic placeholders. They may be recognizable as the components they represent, or they may be volumes for space reservation.”
At a LOD 300 BIMForum says, “the quantity, size, shape, location, and orientation of the element as designed can be measured directly from the model without referring to non-modeled information such as notes or dimension call-outs. The project origin is defined and the element is located accurately with respect to the project origin.”
At this LOD, the modeled object or structure should be able to be confidently used for measurement. Not only should there be accurate measurements, but also details that pertain to what type of surface, type of door/window, etc.
Back to the End-User
As with most things in the industry, the level of development/detail that is to be used is determined by the client and end-user. Within the scope of an entire building model, the client may need different LOD’s used. The client may be interested in replacing all the windows and need the windows modeled in LOD300 and the rest of the structure in LOD100. This is very common. At the end of the day, the value of a 3D BIM model is in its usefulness to the client.
I hope this brief overview of LOD helps clear up any questions that you may have!
Reference: BIMForum.org “Level of Development (LOD) Specification Part I & Commentary: For Building Information Models and Data”, December 2020, Jim Bedrick, FAIA, Will Ikerd, P.E, Jan Reinhardt
Also for more information check out the USIBD. They are another source of great information when it comes to BIM standards.