Basics - Rendering the 3D Model
One recommended method for separating materials in traditional CAD software is to use colors to indicate materials (blue for glass, red for brick) and then have a separate set of layers for each side of the building, such as East Walls, East Windows, East Landscaping, etc. If your views will only show two sides of the building, this allows you to render only those two sides and save the processing time and memory required to render the sides that won't show.
From Modeler to Renderer
Most rendering packages accept models in DXF or DWG format. Many of the problems of getting an accurate model to render properly can be traced to what happens during translation to those formats.
One major issue that you should understand is the need for triangulation, often called "tessellation." For some rendering software, all slabs must be redefined as a collection of coplanar triangular shapes to survive the DXF export/import process. Don't be shocked when you see your beautiful model come into the renderer looking like a cracked piece of crystal. Once it is rendered, you won't see the tessellation lines.
The other major problem is that of "black holes" in your rendered model when a slab has been drawn "backwards." How to correct these polygon "normals" is beyond the scope of this article.
Viewing your Model
First impressions are everything and many rendering packages suffer mightily because the beginner has a hard time manipulating the model to get the view they want. Most packages are leaning toward the mouse-driven click-and-drag method for turning the model and moving closer or farther away. Other programs have quick preset views from conventional viewpoints.
Whatever the case, you can get a good sense of how easy or difficult the program will be to learn by the relative ease it takes to set up your desired view.
Material and Texture Mapping
When you bring your model into the renderer, you will probably either see it as a wireframe model (often triangulated) or else as a kind of shaded model with all the planes "cartoon" colored.
The next step in the rendering process is to assign a material or a texture map to each model entity. Material mapping is more generic where you specify a color, a level of reflectivity, and even a degree of "bumpiness" or texture via a "bump map."
Texture mapping means taking a "swatch" of any scanned material, like brick or roof shingle, which the program uses like wallpaper, repeating the swatch pattern and laying it over the surface of the rendering plane. You can even get a reflection map that will show clouds or the building next door reflected in the plate glass.
Bear in mind that texture mapping is resolution or scale dependent, so if the scanned material is at the wrong size, it could look very funny in your rendering. The more sophisticated rendering programs let your rescale the texture maps to suit.
Many rendering experts say that light sources are the most important factor in making your scene look realistic. With exterior views, there is not much to it but make sure the sun is located in a good position to throw shadows in an attractive way on your model.
Pay close attention to the ground plane that you create for your model. This can give your model an air of reality if your site is more than an unreal, ultra-smooth plane on which to cast building shadows.
For interior views, you will need to create multiple light sources (the more the merrier many maintain). If your system has "ray tracing," the program will literally calculate and follow how light bounces around the environment, creating shade, shadows, and reflections in mirrored surfaces.
Another important component of a realistic rendering is a realistic background for your scene. A generic backdrop with the typical puffy clouds and blue sky adds depth to an image. But clients and zoning boards will appreciate it much more if you have a site photo scaled appropriately behind your model.
You should take your photos with your desired model view in mind. Keep foreground objects to a minimum, and try not to make them too busy so as not to detract from the model that will be sitting in front. A landmark in the photo will help you to pinpoint the correct distances and relationship of the scene to your model as well as the camera angle. You can later edit out this landmark from the photo if necessary.
Entourage, Objects, and Libraries
The other aspect of creating a realistic rendering is populating the scene with people, cars, landscaping, etc. The trick is to find the right balance between the extremes of a ghost town and having your model so busy with other (better detailed) objects that no one bothers to look at your building.
Avoid objects that are too unusual or detailed no matter how appealing may seem. Part of what makes a good rendering program is the quality of libraries that come with it or that are readily available through third-party sources.
Resolution vs. Speed
Once you have a satisfactory model in your rendering program, and as you assign materials or texture maps to your model objects, you will want to see how your rendering is progressing. Because rendering is a high-level computation, you will want to ask for quick renderings to begin with until you are really sure of all the assignments.
Most rendering programs give you a checklist of rendering parameters, chief of which is resolution. The more pixels, the more detailed the image and the longer it takes. Some programs will let your shut off ray-tracing to increase speed. When you have everything set to your satisfaction, then you turn on all the bells and whistles and let your recipe simmer and cook for as long as it takes to finish the rendering.
In years past, it was not unusual for such renderings to take days to finish. Now we get impatient if it takes more than a few minutes. Still, you will need to feel your way as you learn what your computer can handle and what time expenditure makes sense for the finished product you are after.
Once you have a good rendering, the final question is: "Now can I make a movie?" All the same factors noted above apply except multiplied by the need to process and store multiple renderings, each at slightly different viewpoints so that the result can be played back at multiple frames per second for smooth action.
It used to be that one had to write out a whole "screenplay," laying out the travel path and doing wireframe run-throughs, before finally setting the configuration on "cook" and checking back a few days later.
Now with amazing processors at our disposal, a more common scenario is to just move around the rendered model as desired in real time and simply toggle on the "record" button to create an animation file for future play back.
It is amazing that such advances in rendering have come in a few short years. We may be at a wonderful crossover point when many of you will now find it to be easy enough that you are willing to give it a try. Jump in, the water's getting warmer all the time!
Evan H. Shu, FAIA, is an architect with Shu Associates Inc. in Melrose, Massachusetts. He is a frequent contributor to Architectural Record and publisher and editor of "Cheap Tricks," a monthly newsletter for DataCAD users and computer-using architects.
This article is reprinted from the July 2000 issue of "Cheap Tricks" © Shu Associates Inc. with permission of the publisher.