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BIM v. CAD

When I asked you all to comment on my BIM FAQ, I received a interesting comment from Miguel Krippahl. In case you haven't seen it, he suggested the following question and response:

-Is BIM easier to use than CAD?
No. It is much harder, requiring good 3d perception, superior organization, deeper construction and design knowledge.

But is CAD really easier than BIM? I've extensively used both CAD (in the form of AutoCAD) and BIM (via Revit), so I consider myself qualified to attack this question.

First of all, I don't think that BIM requires good 3-D perception. A 3-D object-oriented software program allows the user to view a wall (or door or high rise apartment building) in 3-D (from any angle) or 2-D (any section, any elevation) immediately after placing it in 2-D.
Utilizing CAD, if I want another view of that wall after I draft it in 2-D, I have to draft that view. It seems like CAD requires more 3D perception than BIM.

I'm not exactly sure what Miguel means by "superior organization", but I'm just going to make a few assumptions and dispute the point. In BIM, the design is contained 1 file (where as CAD needs hundreds of files - usually 1 per 2-D document). In BIM, the documents are created directly from the 3D design, so they are already coordinated to a certain extent. Parametric change technology populates design changes to every 2-D document and view (2-D and 3-D alike). In CAD, design changes aren't included in the documents quite so automatically. From this, it seems that BIM is inherently more organized by the software, so doesn't require the user to have this sense of "superior organization".

To a certain extent, I suppose that BIM does require a greater knowledge of design and construction concepts and practices. In BIM, the user is actually building the building in 3D, rather than drafting it in 2D. I don't think that makes BIM more difficult, though. In fact, I found (working as a CAD drafter in an engineering firm) that I had a hard time creating 2D drawings and details of components that I didn't understand.

Lastly, I find that BIM software is much more intuitive than 2D CAD. Although I worked in CAD for about 4 years and became quite a proficient user, I am a much better, much more versatile and efficient Revit user after only 1 year.

Miguel, I look forward to seeing your qualms with this post - thank you in advance for your comments!

4 comments:

RobiNZ said...
This comment has been removed by the author.
RobiNZ said...

(Oops hit the wrong button as I posted, I'll try that again!)
I'm not exactly sure what Miguel means by "superior organisation", he can elaborate, but think BIM does require different and superior organisation skills.

With CAD you're dealing with data but the goal is just a graphic representation. With BIM it's more like database organisation.

The drudgery of things like layer standards largely disappears with BIM but deciding how to craft an object style/family for the best results as an object, not just graphics, requires very different organisational skills.

Miguel Krippahl said...

Ah, great, different opinions :)

First, I want to say I agree with everything you say.

You are right that 2D CAD drafting requires a better 3d perception. I have done some work in rendering, taking 2d files from other architects and turning them into a 3d model (for visualization purposes), and it is usually a nightmare. It takes me sometimes a whole day just to understand volumes, and mostly with help of pencil drafting.

As for "superior organization", I understand and agree with your postulates. It makes sense.

As for design and construction knowledge, I also agree that you do not need more in 3d modeling than in 2d documentation.

So, how come I agree with everything you say?

Because everything you say makes perfect sense in your business: Construction modeling.

My business is design, and that is a whole different can of worms.

If you work with 2d software, you tend to develop your concept on paper, and only go to the computer when you have the basic design nailed down.

If your 2d drafting does not work (mostly plans) then you plot it and draw over it with a pencil.

And, in early stages of the design, you really don't care too much about material, store to store height, construction technology. You just draw two lines (paper or cad) and leave it to later stages to worry about that.

You also tend to compartmentalize design facets. Plans are plans, volumes are volumes, and you mostly develop one to find the other.

With BIM design, this is not so.

Ideally, you start your fist sketches (most of my work is done 100% in the computer, no pencil and napkin sketch whatsoever) with your software, and everything you build is significant.

You can't just put a "generic" wall, the equivalent of 2 lines in 2d CAD. You have to decide on a fair amount of building information, like material, content, height, cost.

The main hurdle about 3d design is, no decision is innocent, no modeling can be done inconsistently.

You have to really pay attention to what you are doing, think carefully on every action, otherwise you model will loose coherence.

This is a major undertaking, not suitable for architects with little experience. Those tend to get caught in the complications of modeling from scratch and forget about design and architecture.

Organization, of course, also relates to this issue. In 2D CAD you only have to worry about the output. After all, the single objective of your files is producing documentation analogous to what you see on the screen. For instance, if you are doing a plan view, The output will be a plan view.

Not so in 3D. A plan view contains a lot of extra information, that will be (automatically) used for quantity takeoffs, sections, maps, other plan views, even 3D renderings.

To have that information available, you have to be very careful in how to organize it, not just trow elements into the plan.

As for better knowledge, there is also the "whopper" issue.

When you develop and document your design in 2D, you tend to avoid the really complicate situations.

For instance, your sections will probably avoid (or accidentally forget...) some prickly spots, that will only be discovered later on,by you guys.

This happens a lot (as you will most surely know), and it there are many reasons for it.

In 3d modeling this is not possible.
Those pesky situations have to be dealt with, because they are easy to detect by us and our boss/client/engineer.

So, you have to know what you are doing, construction vise, and not just pass your problem along.

In a nut shell: modeling for designers and constructors in the BIM worlds is a very different thing, and I maintain that it is much harder to design with BIM than the "traditional" method.

Which does not mean it is not the right way to do. Harder does not mean less efficient.

P.S. Robin
You are mistaking Revit for BIM.
Archicad, for instance, has layers, and I can not imagine life without them. Still, I agree with your "superior organization" definition.

skan said...

You shouldn't compare Revit like programs (Allplan, Archicad) to Autocad but compare them to high end tools, such as Siemens NX or Catia.
With these tools "the goal is just a graphic representation" but much more. You need to take into account contact, mates, constraints, render, light, strength, vibration, manufacturing easiness, etc...