PLQ1.5 – Level of Definition

Hello BIMfans,

After completing my schedule of required Standards last week, I am only one Plain Language Question away from being ready to produce my Employer’s Information Requirements.  So let’s tackle PLQ1.5 and discuss Level of Definition.

Now in a slightly different format to usual, this week I will be tackling Level of Definition with an example; before that let’s define Level of Definition.  Using the  BRE Terminology tool, Level of Definition is:

Collective term used for and including ‘level of model detail’ and the ‘level of information detail’ – PAS1192-2

Ok, now to understand what ‘level of model detail’ and ‘level of information detail’ are, I will refer to work done by NBS with their BIM toolkit; where there is an article that defines both these terms.  In short:

LOD (Level of Model Detail):  Is the numerical value related to the amount of graphical detail included within an object related to the digital Plan of Work (dPoW) stages. Objects start conceptually (LOD2), develop to generic representations (LOD3), then developed further to match the geometry of the specified element/product (LOD4), and finally developed to include supporting detail for construction and installation (LOD5).

LOI (Level of Information Detail):  Is a non-graphical equivalent of the process described above. Objects start with an outline description (LOI2), then develop to include performance criteria (LOI3), then developed further to include information on the specified element/product (LOI4), then developed to include information on any associated (child) products (LOI5), and finally developed to include installation and maintenance information (LOI6).

The simplest to determine is what Level of Information I need.  As I stated when I looked at my Model Purposes and Data Requirements, I will be using my information model to undertake ‘Maintenance and Repair’ & ‘Replacements’.  Therefore I will need installation and maintenance information; requiring Level of Information Detail (LOI) 6. Level of Model detail, on the other hand, is a bit more complex; have a look at this example.

In my home I have an indoor Rabbit called Crempog (Welsh for pancake), he’s a dwarf-harlequin rabbit and spends his day roaming the house (eating EVERYTHING) and at night he stay’s in this cage:

20160502_111653
“Daddy, I don’t give you permission to use my image”. “Silly Crempog, rabbits can’t speak”

As his cage is fairly expensive and takes up a lot of space I will want to capture its information, but I was unsure how much model detail I really need?  So, as usual, I asked Twitter:

With Twitter unsure, I decided to take matters into my own hands and produce a few objects.  Shown here are three different objects that I have created for Crempog’s cage. Each has the same Level of Information Detail, but a different Level of Model Detail.

 Cage2  Cage3  Cage4
LOD: 2 LOD: 3 LOD:  4/5
Time Taken: 1 minute Time Taken:  5 minutes Time Taken:  20 minutes
File Size:  280kb File Size:  340kb File Size:  1104kb

Note:  As there is no Level of Model Detail definition for Animal Housing (Pr_40_30_04, in Uniclass 2015), an assumption was made by comparing pre-defined LOD4’s from Structural Decking where voids are included; and Expansions joints where elements under 10mm are included as justification for modeling the cage bars.  

As you can see by increasing the level of graphical detail it takes longer to produce the objects and the file’s get larger too.  Meaning that any detail above what is required can be seen as overproduction (a waste of effort!); it is important to consider how the cage’s object will be used and seen (remember, visualization was not identified as a Model Purpose).

Typically, models are produced to a scale of around 1:50; a balance between performance, resource, and use; matching the coordination view outlined within BS 8541-3.  Objects within graphical models are normally used to create other deliverables such as drawings.  If you want to create a detailed view (for example, a roof abutment detail) it is much more resource and memory efficient to overlay details over generic model elements instead of modelling every tile, batten, and brick.

For my house, the rabbit cage would only appear on a floor plan drawing, which I expect to be at 1:50 to fit both the ground and first floors on a single A3 sheet.  At 1:50 the cage would have bars at 0.06mm spaced at around 0.5mm.  Plot lines go as fine as 0.18mm meaning my cage would basically look like one big black blob.

And there you have it. By working through an example I have decided that I need my Level of Information to be at LOI6 so that operation and maintenance information is captured to suit my Model Purposes, and I need my Level of Model Detail to be no more detailed than LOD3 to ensure that I only model what I need to show.

This means that I have now answered another Plain Language Question; PLQ1.5 Complete!

Brief:
1.1 Have the modle purposes been defined?
1.2 Are there any specific data requirements to achieve these purposes?
1.3 What format shall the information be delivered in?
1.4 What standards will be followed?
1.5 What level of accuracy/detail/development is required?
1.6 Is there sufficient information to produce an EIR?

Now that I know my required Level of Definition, I need to establish if I have enough information to create my Employer’s Information Requirements to satisfy PLQ1.5…

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