Here http://www.shoegnome.com/2013/03/05/i-was-going-to-write-a-post-about-lod/ Jared Banks refers to relevant discussions of the concept of LOD (level of development), as it is to be applied in BIM (building information modeling).
Here http://www.allthingsbim.com/2008/12/aia-bim-protocol-e202.html , James Van points out that AIA BIM Protocol (E202) is intended “to address the issue of integrating BIM data into the contractual environment.”
Read these articles for a good overview, and then think about what they say.
I propose as follows that what is proposed by LOD will not effectively address the problem LOD intends to address, namely, the lack of confidence one has in the reliability of BIM data; the need to make clear the reliability of a modeled environment.
The LOD system proposes to mark all modeled elements with author ID tags (model element author tags), and author-assigned suitability grades on a numbered scale. The LOD system is item-centric (or element-centric). This is a problem, and not a minor one.
Put aside the practical difficulty of keeping LOD grade values tracked and assigned correctly to every model element (according to their authors), and updating the values as each element evolves, and put aside the practical difficulty of making sense out of a spreadsheet listing every element and its corresponding LOD grade, and ask this question:
What does an LOD system have to say about elements that should be present within a modeled environment, but are not present? What does LOD say about omitted items?
LOD tables are to include notes describing what is omitted. That’s interesting, but practically speaking, notes like that would demand a level of interpretation and intuition from readers and authors alike, and would leave us in the very place we started, having no idea how to ascertain or confirm the suitability of a modeled environment as a deliverable, as a whole, or at any particular location. An LOD table may include notes describing that systems of a certain type are not modeled, or that certain kinds of things should not be expected to be present, or that certain kinds of things may be present in some locations, but not elsewhere, or not completely.
That being the case, when one looks at any specific location in a model, does one have any way of affirming that everything that should be present there (at that location), is present, and that anyone in authority affirms that this is so?
The answer is no. And LOD proposes nothing to solve this problem.
- A minor problem: how does an LOD grade describe a complex single element that has various geometric form throughout the space of its own body, such that the LOD grade should vary per location throughout the form of the element?
- A major problem: how does the sum of all LOD grades for a complex modeled environment add up to a useful evaluation of the suitability and reliability of the modeled environment as a whole?
In both cases, what is missing is a concept of location-specificity.
A design professional must be able to declare that at a location, “I have looked here and reviewed this location, and I declare and certify that all items that should be present here, are present here.
This act is one of the two essential, and not replaceable, things that drawings do, have traditionally done, and that models (BIMs) have failed to do (and that LOD is not addressing).
Drawings allow an author to make directive statements drawing one’s attention to a location and saying, Look at this, understand this, and do this.” This is the first of the two essential (and not replaceable) aspects of drawing: drawings are directive.
The second, of the two essential aspects, is that drawings allow their author to confirm the validity of the directive itself – to confirm that the author has reviewed the location (of the directive statement) and declares that all items that should be present (at that location) are present.
In 2012 Bentley Systems addressed these problems. Bentley has, automatically and comprehensively, infused and aligned the directive statements that are the project’s drawings, into the environment (of the model). By doing that Bentley has taken a very important first step (regarding the formerly ambiguous, archaic, and speechless-like-silent-film modeled environment of BIM) toward converting a modeled environment into a “Directive Environment”
Directive Environments allow authors to be directive in a clear way and say, “Look at this, and do this.” At the same, authors can make clear the locations within a modeled environment at which what is seen is reliable, and differentiate those locations from others. A Directive Environment therefore can be delivered (and received) with confidence, and with clarity about what is reliable, and what is to be seen, understood, and done