Wednesday, April 11, 2007

Parametric Modeling, Knowledge Capture, Knowledge-based Modeling

These terms are frequently referred to when talking about BIM technologies. But few people know the concept and power they enabling us. So I'd like to share my experiences started with this topic.

In a nutshell, they are all about intelligent modeling methods.

To build up a 3D model, BIM model, whatever you call them, in an intelligent way:

1. We should input as less as we could, leaving the repetitive input (drafting) works to the machines - computers.

2. The outcome should be easily modified and managed with lesser effort as possible

In this sense, you will no longer bother which software is CAD(drafting), CAD(design), BIM, 3D/4D/nD modeling - people accustomed to label the softwares they like or dislike with these terms.

To me, how good a software is to what extent it enable us to achieve point 1 and 2 as delineated above.

Back to the terms, Parametric Modeling is the technology itself, it can be used as a general term, or a feature of softwares. Knowledge capture, knowledge-based modeling is the intelligent method we could deploy when modeling, enabled by this technology.

The following is an example: a typical GFA exempted bay window 3D model popularly found in majority residential development in HK. All the instances were built using one single parametric template.

All you have to do is to input the:
1. Width of window
2. Which wall it was located
3. Setting out in plan view

The machine it will give you the cantilevered structures, window sub-divisions, window panes, window frames, wall opening, etc

Why did the computer know what and how to draw all the items you didn't specify?

Because it already know the bay window should be designed in such a way so:
1. To exploit the view (means money in HK)
2. Maximum cantilever span is 500 mm
3. Minimum sprendrel size at top and bottom of the wall allowed by Law of HK
4. Maximum glass pane width is 1400mm (structural concern in common-sense)
5. Enough openable window pane for cleaning purposes (600 mm wide each)
6. 1100mm high protective barrier should be provided for openable pane.

Why it knew?
Because some human being (with professional knowledge) input it beforehand, and these input were re-used when you make your own piece of bay window.

This is what we call knowledge-based modeling. Knowledges and rules are stored (captured) and reused in subsequent modeling procedures.

Is that GOD?
Depends. There may be twenty-something types of bay windows used in a residential tower, but there may only one type of toilet window in the same building. So don't waste time to capture knowledge about that toilet window if you don't find it's style useful to your other building designs.

P.S. This example was done with Revit 5/6, email me if you wanna give it a shot


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