MODELLING CONCEPTS
E-Poles.
Any vertex which has five edges emanating from it is called an E-pole.
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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"
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E-Poles are again very important when creating subdivision surface models but they can also cause the most problems if not dealt with correctly.
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You will find them in internal corners when polygons are extruded. They cause problems with both the subdivision surface modifier and the rendering engines.
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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.
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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.
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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.
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Like N-poles, they are unavoidable and normally indicate several changes of the direction of flow in your topology.
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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.