Nay Ye Oo - Chapter 2: BIM Design Tools and Parametric Modeling

CHAPTER 2: BIM DESIGN TOOLS AND PARAMETRIC MODELING

This chapter basically talks about the origins of 3D Tools and Modeling and its evolution (specifically BIM and parametric), technical methods of how Parametric Modeling works and a few example softwares that dominate the 3D Modeling field. I will be focusing on its origin and evolution.

Early 3D Modeling

In early 3D designing/drafting, there were two prominent methods of solid drawing – Boundary Representation (B-rep) approach and Constructive Solid Geometry (CSG). B-rep uses shapes as bounded surfaces to form solids and featured Boolean operations to modify drawn solids. CSG represents a shape as a set of functions and uses a similar method but without the need to create bounded surfaces. To simplify, the main difference is that CSG uses algebraic formula to define a shape while B-rep stores the result of defining operations and objects. Therefore, CSG solids can be easily edited while B-rep is more suitable for direct interaction. The next step of evolution was from CAD to parametric modeling. This allowed the drawing to adjust accordingly when an edit is made. What this means is that, after the user initially designs/draws an object, any new changes made to the object such as reducing a length or removing a portion of the drawn solid, the parametric model will be able to automatically generate a new solid without the user having to make the necessary adjustments to the initial edit.

Parametric Design/Modeling

Typically, there are 3 degrees of parametric modeling: simple, minor & major improvement. Simple just requires defining shapes or assemblies with parameters. Minor improvement adds more detail to the defining stage so as the drawn solid would automatically update when the predefined shape’s parameters are changed. Finally, a major improvement adds a greater level of detail that lets a drawn solid interact/communicate with another drawn solid’s parameters. The common uses of parametric modeling discussed are for buildings and construction.

There are two types of objects drawn - pre-defined base that has various object “families” typically used in BIM Architectural Design Applications and built-in features to draw. An example drawing of a precast fabrication-level architectural façade can be seen below.

 Figure 1. Precast Fabrication-level Architectural Facade

User-Defined Parametric Object Anomalies

There will always be a case where a very customized drawing is desired. Such a situation is outside of the not just the pre-defined objects but also outside of the capability to be drawn using the provided tools. When such as case occurs the primary method of solving it is to draw it in another system and importing it. An alternative is to use solid modeling geometry and assign attributes manually.

Summary

CAD and BIM are great assets in modern design and construction. However, CAD is more rugged in nature compared to BIM. But to each, there is its own benefit and disadvantage. BIM has become more and more popular in the engineering industry and it is widely becoming the new norm for designing, be it in the civil, architectural or mechanical field. Even other areas of engineering is relying on parametric modeling as it has an easy interface/platform and great functionality in generating renders.

COMMENTS:

Dung Tran:
I read your post just to see what you took away from Chapter 2. I too had the same chapter assignment. I'm glad that you focused on the actual application of BIM program and elaborated on Revit. It's nice to know that Revit or AutoDesk are starting to compile these gigantic libraries that will allow most of their various softwares to be able to communicate with one another. This was an issue at my first co-op where I used Microstation, Bentley while PWD and Philadelphia Streets used AutoCAD. Converting one file to the next is not impossible but it sure is a tedious and inefficient task. So I for one, am happy to see that we are making great advances in this sector.

Andrew Maita:
It was very informative to read your post as I had no clue what interoperability meant. I think you did a great job at explaining it in as much not technical terms as possible. The idea of it is great and I can see why all these drafting applications are trying to incorporate this feature into their systems. I guess the main issue at hand would be how to update old softwares that do not read different types of files that is new to it. This sounds like a cumbersome task where redesigning the whole software might even seem easier.

Source: BIM Handbook : A Guide to Building Information Modeling for Owners, Managers, Designers, Engineers and Contractors by Eastman, Charles M. 2nd Edition. Hoboken, NJ: Wiley. 2011