When modeling with polygons, it is important to form all your models using quads and triangles. A quad is a quadrilateral, or four-sided polygon. A triangle is a three-sided polygon, sometimes referred to as a tri orface. An ngon is a polygon with more than four sides.
Ngons (left) and quads (right)
While your 3D application probably allows you to create models with ngons, models created in this way are undesirable for a number of reasons. You can make your 3D model more appealing to a much wider audience of customers if you set it up with mostly quads and a few triangles where needed.
Why Should I Fix My 3D Models?
It's true that if a customer doesn’t intend to map, export, or subdivide your 3D model, then ngons don't present a problem. You could take the attitude that the customer can fix it up if he/she needs to. However, using only quads and triangles will provide maximum opportunity for sales of your 3D models.
The majority of our customers, by survey, want a 3D model that they can use immediately in their workflow. When comparing two comparable models for purchase, a customer is more likely to purchase the one that has only quads and triangles because it will work in any workflow, now and in the future.
Why Ngons are Undesirable
A model made with ngons can present several problems for an artist trying to use the model. Here are a few of them.
Mapping and Unwrapping
It is very difficult to correctly map and unwrap a model made with ngons.
Subdividing a model with ngons can ruin the shape of the model, introducing pinching and creasing in renderings. Artists expect to be able to subdivide a model if they need to.
Let’s illustrate the subdivision problem with an example. The image below shows a simple model with multi-sided polygons, and the resulting rendering. The model looks fine when used in this way.
The next image shows the model after TurboSmooth, a commonly-used subdivision tool, has been applied to the model in 3ds Max. In the rendering, where you can see the pinches and creases that were introduced simply by subdividing the model.
Now let’s look at the same model, identical in shape except that now it’s formed completely from quads and triangles. Here, you can see that subdivision works as expected, making the model smoother without affecting its overall shape.
Creating 3D Models with Quads and Triangles Only
Many modeling methods allow you to create polygons with more than four sides. In your 3D application, you will also find tools for detecting multi-sided polygons and manually breaking them down into quads and triangles. See the videos above for information on how to detect and fix ngons in your 3D application.