Thursday, March 01, 2012

Moving Forward with LOD

I first wrote about LOD (I’ll break down the acronym later) and the AIA E202 BIM Protocol Exhibit in a post from December 2008, but the topic is such an important part of doing BIM right that I wanted to bring it back for further definition. Here we are three years later and I am reflecting on the last statement of that post…

“[The BIM Protocol Exhibit]…has not yet become a formal addendum to any of our project contracts.  That will likely change very soon.”

Since early in 2011, I have been participating in a work group that was spawned from the AIA and the AGC BIMForum to further expand upon the LOD definitions. That is to say, if you are a designer, engineer, or builder and you are asked to provide model elements at LOD### – do you know what you are required to provide? The group will be presenting a progress update at the upcoming BIMForum event in San Antonio, Texas, but for now, allow me to share some insight I have gained while involved with the group.

What is “LOD?”

First, let’s get our terminology straight. According to the AIA E202 document, LOD is defined as “level of development.” It does NOT mean “level of detail;” however, this is an important concept. Unfortunately, the choice of words makes for increased confusion over the acronym, but there definitely is a difference.

Level of detail is the amount of information and geometry provided by the content author or other project participant. There can always be a higher level of detail in a project model than what is realistic to be used by others in a downstream workflow. Level of development is the maximum amount of information and geometry that is authorized for use by others.

Expressed in different terms: DETAIL = INPUT and DEVELOPMENT = RELIABILITY

No Such Thing as an “LOD### Model”

I mentioned this in a recent post about the ‘fluffy kittens,’ but allow me to reiterate the point that LOD is based on assemblies – NOT entire models. In my opinion, the easiest way to understand this is to separate the milestone deliverables from your thinking about LOD’s. In other words, don’t think that schematic design = LOD100; design development = LOD200; and so on.

At any given project milestone, you will likely have a combination of LOD’s. For example, at the end of construction documents, the interior walls and doors might be at LOD300, furniture is at LOD200, and information about electrical fixtures is only supplied as an allowance per square foot; thus LOD100.

Let me explain this a little further with an example many firms are using (including some folks at HOK). Below is a screenshot from an LOD modeling guide offered by one of the participants in the LOD work group. I won’t use the person’s name or the firm name, but I certainly do not mean any disrespect by using this example (many others make the same assumption).

image

In this image, a progression in LOD is assumed to be aligned with the development of the project design – probably from SD to DD to CD. However, if you look closely at the difference between the 200 and 300 plans, elements like the plumbing fixtures seem to be the same model object. How can that be if the deliverables are at two different LOD’s? What if instead we label the plans as “SD Floor Plan,” “DD Floor Plan,” and “CD Floor Plan?” In the example above, you might know exactly what manufacturer and model number the plumbing fixtures will be (‘buy it’), so that assembly will be listed at LOD300 in the DD and CD deliverables.

In contemplating the LOD concept as it relates to any assembly or component in a project model, I developed the following (although I’m still working on a better explanation for 100):

  • LOD100 = Interpolated calculations (estimates)
  • LOD200 = Specify it
  • LOD300 = Buy it
  • LOD400 = Build or install it
  • LOD500 = Operate or maintain it

The above list simplifies the concept of authorized uses. Essentially, what you should be able to do with an object given a certain amount of input information.

Does LOD Imply Time?

Another misconception about LOD is that it implies an ‘in progress’ state of content. For example, you might think that LOD200 means that you are placing manufacturer-specific content in your model, but you are still in an early phase of design such that quantities and locations are not finalized. In this case, the correct LOD assignment would be LOD300 with the understanding that at design milestones quantities and locations will be in flux.

Here’s another twist, if you are working on a project that will be competitively bid – essentially, design-bid-build – what LOD would you use for final construction documents? If you think about it, specifications for bid projects usually allow for (or require) a list of alternate products (Wicks Law, New York state). As such, even if you are using a model component provided by a specific manufacturer, the level of development (reliability) can only be at a generic level – LOD200. This may seem counter-intuitive, but a full understanding of these levels is going to form the foundation of ‘good input’ for the industry to start realizing improved interoperability.

I invite you to read more about LOD at the Vico Software website, BIModal Evolution blog, Revit Sticky Notes, Revit OpEd, The BIM Manager, and Q5 (Tocci). There are also some good discussions happening in the BIM Experts group on LinkedIn.

14 comments:

  1. Good article, but I'm still not in total agreement with LOD500 being "operate or maintain it". A coffee pot that looks like a cube with an attached pdf manual can be operated and maintained, but could never be built. So does a LOD100/200 Revit family automatically become a LOD500 when you attach a pdf? According to E202, LOD500 includes everything before it.

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    1. Brian - you raise a really good point, one that I've discussed with Markku Allison at AIA. They originally thought of LOD500 as automatically including all levels below, but as you state, this might be too much info for an owner. Do you need a fully-detailed model of something in order to maintain or operate it? Depends. For mechanical equipment, I would say yes. For a coffee pot, probably not.

      Thanks for your comment!
      JV

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    2. This is a great point and usual point of friction. I think this is where a better definition of BIM as process vs. BIM as product is necessary.

      The teapot is a product of the BIM process. If the BIM process intended to go through LOD 100 through LOD 500, one can assume that the 500 level teapot would then include all preceding levels of reliability. Yet, if the process was only to prepare an LOD500 model then this assumption no longer applies. The model would probably be purpose-built for that level in a cube + pdf method, including whatever information was requested of them and nothing else. Each project should specify the process intended in their BEPs.

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    3. Maybe there should be a "omitted" column for LOD's to "not-include" items.

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  2. Great post. I need to send this to folks I've been arguing with for a while. Maybe you can make my point where I can't

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  3. I never really considered the Levels of Development as a necessarily a progression from one end to the other. The E202 doesn't specifically call for a LOD 500 element to include the information expected in a LOD 400 element. This is especially true in a Design Bid Build environment where you might develop a model to LOD 300 and bid it; then take that model to a LOD 500 for the owner to use in operations. If the contractor was never using BIM, then all of the 400 LOD information would be irrelevant to the owner as long as the LOD 500 information was accurate. So a tea kettle need not include manufacturing data to get to an operations level of development. I mean, I bought the tea kettle... why would I want to keep information on how to build a replacement around?

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  4. James, it also looks like "LOD" has something to do with satanic ritual killings : - )

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  5. Great post, as always, :-) its interesting, which is why are asked you question on Monday, about aligning LOD with the process, because in that particular case the client had cherry picked the BIM deliverables that he thought he would get at the initial design option stage SD, with optioneering studies. There was no way that this could be achieved, so I suggested an LOD 150, which spanned between 100 & 200 to allow for certain aspects of the initial BIM options to be requirements to be delivered. Some of the requirements where so way off, because development of the BIM over time was not sufficient enough & the scheme certainly wouldn't have the refined enough to allow this to happen. So whilst I do agree that LOD does not imply time, it gets blurry as understanding what needs to be delivered at a particular time some how does become a time related issue. In the case I am describing, you could not do logistic studies until the form of the building had been defined, unless it was directly connected.

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  7. This is better then the last one you did, very informative

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  8. LOD 100 should be only massing model no any design

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  9. LOD = 666 (RTCUSA Pool)

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