Modeling a head with proper topology - Part 1

As a creative application, Maya contains an entire suite of tools that allows you to create 3D objects and characters out of polygons.
However, simply assembling polygons in a manner that resembles your idea isn't enough. It's also important to build proper topology.
Topology refers to the direction and contour of the edges on your mesh.
Maintaining proper topology is just as important as the overall shape, because without it,
geometry and textures may warp and distort during animation.
For example, let's take a look at this zombie head.
At first glance it looks okay. It certainly looks like a head, especially with its cartoony exaggerated facial features.
However, if we look at the mesh, it soon becomes apparent that the topology is a mess.
Let's take a look at some of the problem areas.
First, notice the general flow of the edges.
They wrap from the front to the back and top to bottom, much like a primitive such as a cube or a sphere.
However, when building a face, you generally want edge loops to circle around the major features,
such as the mouth and eyes, and progressively expand outward to the rest of the head.
This follows the muscle structure of a real face, which helps maintain volume under deformation.
It's also important to note that while the suggested topology works well for this face,
facial structures in general can change slightly depending on a specific character's facial features.
For example, the topology of an old man's face may need to account for details like wrinkles,
bumps, and imperfections, that do not appear on a young woman.
Next, notice that there are quite a lot of tris and n-gons on this model. A tri is a face with 3 sides, while an n-gon is a face with 5 or more.
In general, you want to keep your models limited almost entirely to 4-sided faces, otherwise known as quads.
The reason for this is because tris and n-gons pinch unpredictably during subdivision,
problems which become magnified in animation.
A better way to control pinching is to control your poles. A pole is any vertex where 3, 5 or more edges intersect.
Poles are actually a natural and necessary occurrence when you need to redirect your edge flow,
such as where the loops around the mouth and eyes meet.
Because poles pinch predictably, you can put them in places where the pinch is not only less prominent,
but can actually be used to your advantage.
Now in the course of your modeling, you may find that keeping to all quads might not be possible.
In these situations, it is acceptable to have a few tris, preferably hidden away where they can't be seen,
but n-gons should always be avoided by converting them into quads.
This isn't always a straightforward process, but in the long run the extra effort will always be worth it.
Finally, notice that in certain spots the spread of vertices is not very even,
particularly around the ears where the mesh suddenly gets denser.
In this case, it looks as though someone took the ears from an existing, high resolution head, and pasted them in here.
Although this may seem like an efficient workflow, particularly for hard to shape body parts,
it's important to keep the relative spread of vertices on your meshes even. This will keep the deformation more consistent.
Now if we had to fix this head, it might take us quite a long time, since we'd have to redo nearly the entire topology.
Instead, let's look at a few things you can do during the modeling process to avoid these problems in the first place.
You can start a model either by building a polygon in the front and side views,
or starting with a primitive and molding it into the shape of a head.
In either of these cases we're going to need a guide.
Switch to the side view. Let's load a 2D reference plane.
Select View > Image Plane > Import Image, and then navigate to the Zombie_side file.
Maya loads a 2D profile picture into the scene.
Now go to the Attribute Editor for this imageplane and lower the opacity a bit so we can see our mesh through it.
Also, let's turn it off in all the other views.
Now do the same thing for the front view.
We're going to use the Polygon Creation method in this example.
Starting with the side view, use the Create Polygon Tool and create a number of points to outline the head.
Be sure to place the same number of vertices in the upper and lower mouth areas. You'll see why later.
Now we have a basic silhouette of the head.
Let's extrude the face by selecting it and holding Shift + right-clicking and selecting extrude.
Use the manipulator to pull the face out a bit, and then delete it.
This leaves us with a thin ring of faces in the shape of the head.
Now that our head fits the side view, we need to extrude it to fit the front view. The two views combined will give us our 3D shape.
However, let's remember the first rule about good topology. We want to build rings around the major features.
To accomplish this, we're going to start at one of those major features, the mouth, and slowly build outward in a ring pattern.
Select the edges around the lips and inner mouth and extrude them a few times. Use the Front and Side View images as a guide.
Now that we've come to the edge of the mouth, this is where we really start creating our loops.
Select the Append to Polygon Tool from the Edit Mesh menu.
Now select the two outermost corresponding edges one at a time.
Maya creates a polygon between them.
Repeat this for each set of adjacent edges.
You'll notice when we reach the innermost edges, an appended polygon will create a tri,
which we'd prefer to avoid.
We've fallen into a trap of modeling. Even though the 2D drawing shows a sharp point here, we should really have 2 edges.
In general, sharp points that are expected to be animated should actually be represented with small square shapes.
Thankfully we can fix this with the Insert Edge Loop tool.
Select this tool and then click along the edges directly above the sharp point.
Then use the Move Tool to move the new edge into the correct position.
Now you can append them like the rest.
If you take a moment to double-click one of the edges around the lips, you can see how they flow in a proper ring pattern.
Now you can select all the outer edges on the lips and extrude again to pull out another ring.
Now we need to merge this new edge ring with our existing vertices. We'll use the Merge Vertex Tool.
Click and drag from the start vertex to the end vertex and Maya will join them. Now do the same thing for the bottom lip as well.
Now let's extrude the bottom of the nose out.
We've reached an interesting problem here.
Since the span of the nose is so much smaller than the span of the lip, our edges don't match up nicely.
If we tried, we'd have a really dense pair of edge rings.
Instead, let's try a different strategy. Extrude the two outer edges of the lips.
Now use the Merge Vertex Tool to join the vertices at the base of the nose and the new edge you just extruded.
Notice that the hole you're left with has exactly 4 sides! You can now append this just like you did before.
Often times when modeling you will need to come up with creative solutions like this.
Every situation is a bit different, but just remember that your main goal should be to preserve the rules of good topology.
Maintain proper edge loops, keep to quads, control your poles, and keep consistent spacing between your edges.
Now bear in mind that this is just a start and far from complete.
You will need to use the move tool to massage some of the vertices to smooth out the shape.
Eventually we'll add more subdivisions to give you more precise control of the overall contour of the mouth.
We'll also need to soften the edges so that the creases don't show up.
A properly cleaned version has been included with the files for this tutorial.
In the next video, we'll look at how to create proper topology for the eyes, brow, and the rest of the head.