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Maya Modeling: Polygonal Modeling Theory

By Jahirul Amin
Web: Open Site
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Date Added: 24th July 2013
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1754_tid_mainimage.jpg

Before jumping into the deep end with modeling, let's take a look at some modeling theory in the shallows.


Introduction

Before we start modeling, I just want to touch on some basic but essential polygonal modeling theory. If the geometry needs to be taken into a sculpting package or animated, a clean mesh is crucial. On top of this, well-executed topology produces fewer artefacts during render time. In short, a polygon in time saves nine.

Step 1: Quads v Tris v N-gons

So what is the difference between a quad, a tri and an N-gon? Well, a quad is any four-sided face, a tri will have three sides and an N-gon will have anything more than four.

Out of the three of these, it is highly recommended that you try to keep everything in quads. Generally, they subdivide more predictably, deform better during animation and you encounter less texture distortion.

If you need to use tris, then it is best to try and hide them in places where they are less likely to be seen, such as under the groin or armpits on a character.

N-gons, on the other hand, should be a no-go zone. When subdivided, N-gons can cause pinching in the renders and can be a pain when weight-painting during the rigging stage.

Taking a model that is predominantly made of quads will also transfer better to packages such as ZBrush and Mudbox.

1754_tid_fig_01.jpg
The joys of quads and the terror of N-gons


Step 2: Uniform Geometry

Uniform geometry means that we are trying to keep our polygonal faces as square-like as possible, and space them as evenly as we can across the surface. Doing this makes weight painting at the rigging stage easier and leads to better deformation during animation. You will also get less distortion when applying textures, although the importance of good UVs will also be a factor in this.

To help you get the geometry uniform, Maya has the wonderful Sculpt Geometry tool. Setting its Operation to Relax should allow you to iron out the edges.

1754_tid_fig_02.jpg
Using the Sculpt Geometry tool will help to even out the edges of your model



continued on next page >

 
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Readers Comments (Newest on Top)
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3d User on Sat, 27 July 2013 5:53am
About N-Gons... First, the use of N-gons was clearly demonstrated in the Catmull-Clark white paper in 1978. The paper also states that the subdivision surface will be C2 everywhere and AT LEAST C1 at extraordinary vertices: meaning where you will have a vertex that has 3, or 5 or more edges coming off it. This is the pinch you are refering to. Second: Every subdivided surface has TWO possible coarser level that will create it, one with quads and one with n-gons. Try it on paper (reversing the subdivision algorythm) and see that this is true. Third: The LEGEND that n-gons are bad comes from early rendering technology (like mental ray in the 1990s) that would use shortcuts in the computation using only quads and did not support triangles or n-gons. At the time, n-gons where bad, but things have changed, it is time 3d artist keep up with the current art. What it Means: The edge flow of a model leads to extraordinary vertices, it is unavoidable. When you accept the fact that 3-junction tends to bunch up polygons, make that area larger, or, use a triangle if the arrangement skews your edge flow. The same goes for 5-junctions or pentagons. The evenness of the model should also have a measured resolution (how long are the edges) which relates directly to what your detail resolution really is and what you leave for your texture work. Bringing models to another package poses a problem if you are using n-gons, they will not work with z-brush or mudbox, however, sending a subdivided model (only one level) will work perfectly. Note that MODO supports n-gons and has sculpting capabilities superior to Maya. Using n-gons is an expert thing, that once mastered, brings about a freedom you didn't have before. At that level, 3d artist also separate shape and topology, and take full advantage of resufacing (retopo...) softwares. Separating the art from the technique elevates the quality of your models above what you think is possible, something that follows your artistic and technical needs in all aspects of the creation of a model. Finally: More experienced users should start writing tutorials other than the basics and give a chance to educate the field properly instead of steady regression I have seen in the last decade.
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