Cheap Trick of the Month From Cheap Tricks, May 94 Issue Published By: Shu Associates, Inc. 120 Trenton St., Melrose, MA 02176-3714 (617)662-0020 (FAX Same) eshu@world.std.com

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Working with 3D & 2 1/2D

As design professionals, we pride ourselves on our 3D visualization skills, yet many of us throw up our hands trying to understand how to work with 3D on our computers.

In explaining how to work in 3D, we find that the key is to first burn into your brain some basic concepts about 3D. In our June ’91 issue, 3D Thinking, we impressed upon you the concept that typically, your 3D model stays fixed in space, while you move your view (or picture frame) around it in order to find the right point of view for further elaboration or editing.

Perhaps even more basic then that lesson is to understand the difference between 3D and what we call “2 1/2 D”. When we first draw a plan in DataCAD, we understand that we are drawing in a 2D or flat, ortho mode. The wonderful thing about DataCAD is that we can immediately go into a 3D view, and wonder of wonders, we have real 8' high walls. DataCAD automatically assumes that all of your lines have a z-height of 8', since most initial lines drawn are walls and 8' is a residential standard. (The “z” dimension is the vertical height in 3D space, where x & y are the planar dimensions.)

The key concept to understand here is that this 8' of z-height is called an “extruded” height or in CAD nomenclature, 2 1/2 D. The reason it is not true 3D is that we have not given the computer enough information to know what kind of a 3D entity it is.

For example, if you draw a simple 10' x 15' rectangle in plan and look at it in 3D, you see a box. But the computer does not know whether it is a solid block, or whether it is an empty box with 6 rectangular polygon sides, or whether it is whether it is an box without top and/or bottom, or whether it is simply a wireframe of 12 lines linked in space. Because of this lack of specificity, when you try to edit your 2 1/2 D entities with the 3D editing tools, the program will tell you that it can’t find anything to edit.

Now, all is not lost. You can still convert your 2 1/2 D into true 3D. In DataCAD, you will find an “Explode” command in your 3D Edit Menu (see DataCAD Tutor this month for a discussion of the 3D Menus.) This command will allow you to convert your 2 1/2 D entities into either 3D polygons or 3D lines. In our rectangle example above, you could tell the computer to make your rectangle into a “box” (with no top or bottom) or a “wireframe” (but note that you do not have the choice to make it a block or a box with either a top and/or a bottom.) Once “exploded” or converted, you will find that you now can edit, stretch, move or otherwise manipulate this items in 3D space with your 3D editing tools. However, you have already been limited by your conversion choices. For this reason, when you try to convert 2 1/2D to 3D, your walls will never be solid slabs and your windows will not be true 3D voids.

Where is all this discussion leading, you ask? We would like to propose a distinction in your minds between 3D Viewing and 3D Modeling. Think of 3D Viewing as a design tool. Think of 3D Modeling as a production and marketing tool. 3D Viewing (as shown below) is for developing your design ideas, laying out sketch perspectives, and for getting a feel for your design. 3D Modeling is for photorealistic renderings, for 3D Working Drawings (see Dec ’92; Dec ’93; Dec ’94), and for finish perspectives.

For 3D Viewing, using your normal 2D menus and always being aware of your current z-base and z-height settings, you can use your normal 2D tools with perhaps adding some true 3D roof planes to develop quite a nice 3D Viewing model. That is to say, this model can be viewed like a wireframe with even some quick shading looks to give yourself a powerful design tool which can be readily manipulated. You can use your Change menu to modify your z-base and height for any entity to move it up or down in 3D space. We use this technique extensively for our own architectural work.

As noted in our January ’94 issue, architect Neal Mortenson of Sydney, Australia has even simplified this process further by developing his own “single line” wall technique (see figure at right). As long as you are aware of the limitations of 2 1/2 D, this 3D Viewing technique can take you a long way.

However, when you do want to go to that next step of having a 3D model which will render and hide correctly, it is best to work completely with true 3D entities in a 3D modeling technique. We suggest using your 2D plan layers as simply guide layers on top of which you build in 3D space using actual 3D entities such as horizontal and vertical slabs, blocks, polygons, 3D lines etc. It is helpful to “squash” your plan layers flat (i.e. z-base and z-height = 0) and even change all the 2D lines to a neutral blue color for example, so that you can readily see what you are building on top of in 3D space. For this reason, we often export our guide plan layers out and work on our model in a completely new drawing file.

These basic concepts of 2 1/2D vs. 3D and 3D Viewing vs. 3D Modeling are key to using and understanding the powerful tools of 3D visualization.