MODELLING CONCEPTS
E-Poles.
Any vertex which has five edges emanating from it is called an E-pole.
As with the N-Pole, a usefull way to remember which is the N-Pole is to visualise 5 matchsticks used to make a capital Letter "E". it can be made with five matchsticks"
E-Poles are again very important when creating subdivision surface models but they can also cause the most problems if not dealt with correctly.
You will find them in internal corners when polygons are extruded. They cause problems with both the subdivision surface modifier and the rendering engines.
In the example below there are two extrusions. The extrusion on the left was made by selecting a face and pressing "E" to extrude it upwards. You can see from the object at the bottom, which has a subdivision surface modifier applied to it, that there are some problems with the shape. There is no good way to control the curvature around this extrusion as the 5- spoked pole at the bottom will always get in the way and cause problems.
The extruded face on the right has been protected with a border region by using the "outset" operation on the face before extrusion and will render correctly with good control over the curvature around the base of the extrusion.
Extrusions should be protected with a border to ensure correct flow and control
A demonstration of the problems with N-poles and how they can be avoided can be seen when we create an object for use in a softbody simulation.
Like N-poles, they are unavoidable and normally indicate several changes of the direction of flow in your topology.
The extrusion of polygons is normally the cause of problematic n-poles so extruding polygons is avoided. We extrude loops, or islands of polygons surrounded by loops, NOT POLYGONS.
I will show many various ways to handle E-Poles throughout the video tutorials.