TERMS:

• Polygon: A triangle unit for building 3D forms. A "quad" = 2 polygon "tris."
• Normal: The direction the polygon faces, represented by a perpendicular arrow (normally invisible).
• Modular: Geometry with a consistently unbroken surface.

HYGIENIC (Clean) MODELING:
“Unclean” geometry is where the model is no longer Modular. When geometry is Unclean its surface can display strange shadows, change shape unpredictably when animated, and break when advanced techniques like Boolean are applied. Ways that the surface can be Unclean include:

1. Internal Geometry: All models should be a hollow shell. Occasionally you will find polygons crossing through your shell, sometimes with vertices attached both to one side and the opposite side. These must be deleted.

2. Duplicate Vertices: What appears to be a single vertex is actually two or more in the same space. These must be welded/collapsed.

3. Coplanar Geometry: Two polygons occupying the same space, sometimes with Normals facing in opposite directions. One of these polygons must be deleted, or bad “flickering” will appear in the render.

4. T-Geometry: Planes that intersect without being connected by vertices (essentially, one object just stuck into another and attached, without being connected to create a consistent, modular surface). Both objects can be Cut at their intersections, the internal geometry deleted, and the matching vertices welded, or they can be detached and Booleaned into each other.

WASTED GEOMETRY:
Vertices sitting on straight lines on your model which do not contribute to the form represent wasted polygons. In both real-time game projects and pre-rendered film projects these wasted polygons cost money and resources, and must be eliminated through collapsing and target welding vertices.


 

AVOID LONG POLYGONS:
Long polygons often cause problems with lighting and shadows. Most rendering systems calculate lighting by the location of vertices, and if these are too far apart the space between them will have difficulty lighting properly. The solution is NOT to add wasted vertices along the surface; instead, design your forms with more variation and detail.


 

GOOD CURVES AND SILHOUETTES:
If a part of your model is meant to be curved, be sure there are enough polygons to make the curve appear smooth.


 

CHARACTER MODELING:
For all characters, the following three principles must be applied to create forms which will animate smoothly:

1. Even Tessellation: Be sure to evenly space the divisions on all the parts of the body, so that the upper arms, lower arms, upper and lower leg, and torso have roughly even spacing. Joints and the face will have higher tessellation, but still be internally even.
2. Quads: Work toward only four-sided shapes everywhere on the body (two triangular polygons). Avoid triangles where possible, and absolute be sure to cut down all shapes more than 4 sides (N-gons)
3. Edge loops: Cut lines on the body to enhance animation: straight circles around the limbs and torso, concentric circles around the mouth and eyes.

CLOTHING WRINKLES: A well-sculpted character model creates a strong silhoutte using large clothing wrinkles at break points (like where pants hit), bunch points (like where a shirt tucks into pants), or hang points (like where the sleeve and torso of a short make long creases originating at the shoulder). The type of cloth can be indicated by Three Wrinkle Properties, all of which should be referenced in your model from real-life sources:

1. Wrinkle Thickness: Thicker clothing (wool) typically create laregr wrinkles at break and bunch points. Thinner clothing (cotton) makes thinner wrinkles.
2. Wrinkle Spacing: Stiffer types of cloth or areas of a piece of clothing will have fewer wrinkles with greater distance betwen them.
3. Wrinkle Depth: Thicker/rougher clothing creates deeper wrinkles; finer cloth (silk) smooths itself out.

DETAILS:
When creating a detail like a fold in clothing, remember to cut in at least two lines, so that one can stay put and the other can be pulled out to create the fold. The transition between clothing and skin, like a sleeve, is at least two lines: the line of the bottom of the sleeve and the line where the sleeve actually touches the skin.


 

ANGLES:
A 90 degree corner should be Chamfered so it does not appear too sharp. Obtuse angles (greater than 90 degrees) are ALWAYS better than Acute angles(less than 90 degree) and 90-degree angles for visibility and overall appeal. A common error is to leave a sharp edge at the botom of sleeves, dresses, etc; these edges should be chamfered or the program will create shading artifacts.
3ds max: Use Bevel instead of Extrude for small details on a surface to make them read-able.


 

SMOOTHING:
The type of modeling edvocated here does not use any kind of meshsmooth tool, which is percieved as "melting" the model. Every detail and curve should be cut in by hand. Do use polygon smoothing tools, though, to create polished surfaces:
3ds max: Use Polygon Smoothing Groups to create unified surfaces on big forms. On a character, for example, all the skin can be one SG, the pants one SG, the shirt one SG, the belt one SG.
Maya: Select edges and open Edit Polygons / Normals / Soften/Harden to create divisions between smooth forms. In most cases, just using settings of 0 (hard edge) or 180 (smooth) is sufficient.