What is wrong with 6-sided poles?
Poles can unintentionally redirect or terminate edge flow of a model’s geometry. Ring selection of an edge reveals how the edges flow. Usually, ideal edge flow runs in a smooth grid like pattern, top to bottom and left to right. If the ring selection ends quickly or only flows in one direction, it can be an indicator of how difficult the mesh will be to work with or edit.
Grid like edge flow is more ideal for hard surface models and not necessarily on organic models, such as faces of characters. Shape and detail of the model should still dictate edge flow and while avoiding 6-sided poles.
Poles can also create pinch points causing artifacts in smoothing and UVing. While less noticeable on flat surfaces or dull materials, there may still be artifacts as the result of poles existing in the geometry. These artifacts are often visible in renders as wrinkles or creases in the surface where it is expected to be smooth. Pay attention to unexpected warping in highlights or shadows.
Fix Existing Poles
There are many ways to fix already existing poles on a model depending on how many edges it has. It is far easier to work with an even number of edges when trying to avoid triangles and poles. On a cap with 6 or 8 sides it can be as simple as selected every other edge between triangles and deleting them. This leaves even quads on the cap. Worst case when fixing poles is having to draw new edges after removing some of the previous ones. Care needs to be taken with creating new edges where the pole is not a flat surface. How the geometry is drawn will affect how it smooths.
Rounded shapes or details embedded in a model’s base geometry is usually where poles will occur. Working with an even number of sides makes tying the quads of those details into the edge flow of the rest of the model much simpler most of the time. When dealing with more complex geometry it is important to be conscious of where poles may appear. It is possible to have poles created from quad faces meeting. These types of poles may require more complex drawing of edges to fix. Let the model’s shape and surrounding edge flow dictate how best to eliminate the pole.
Always remember, it is easier to eliminate poles and geometry problems at the beginning while working. It is easy to ignore a pole on a small detail, but once that detail has been cloned and arrayed into something complex, removing poles can become an overwhelming task. Many times it may even be faster to remake geometry from scratch correctly than try to fix what is finished.
Quick All-Quad Spheres
A base sphere made of all quads can quickly be created by starting with a single segment box or sphere primitive set to 4 sides. Apply a smoothing modifier over this base shape to create an all quad sphere. As iterations increase the sphere density exponentially increases. Then simply convert the object to an Editable Poly. The newly created sphere is 100% quad geometry with clean edge flow, perfect symmetry, and has no poles.
NOTE: Exceeding 3 iteration is not recommended. This will create extremely dense base geometry which will be more difficult to work with.