my flimsy attempt:
if you use a smoothed proxy mesh and compare the proxy wireframe to the smoothed mesh, you will notice that the smoothed mesh has a certain flow.
when the polygon is a quad sided face the mesh flows smoothly in parrallel to the edges.
but with tris and n-gons the faces have been subdivided in odd ways to ensure they are quads. this disrupts the flow of the mesh. but its also not a huge deal and can be advantangeous at times.
Using a human face for example, you will notice that the movement of any underlying muscle results in the compression of the fatty surface above it.
The eyes have an elliptical compression pattern, and depending upon the expression, crows feet wrinkles radiating out from the corners of the eyes.
The lips (if you open up your mouth widely you can see this) are actually a ring of flesh, not two halves. They deform in a circular pattern.
The creases for smiling, ignoring the amount of fatty tissue built over them are created by several muscles pulling back on that portion of the face.
In order to actually express all of these (and tons more) muscle movements, the mesh needs to be arranged in such a way that it can be compressed into the proper forms. Ie. in circular patterns radiating from the eyes and lips, and
This is were edge loops come in. And edge loop is a continuous (though not necessarily a loop) string of edges, layed out to ensure proper deformation and surface flow.
these images are leached and will be taken down shortly.
(image credit Bay Raitt)
(image credit Steven Stahlberg)
A good edge loop layout will also aim towards maintaining all quads, reducing surface deformations due to the smoothing algorithm and issues with texturing.
Here is a good example of very complicated edge loop structure (http://www.cgtalk.com/showthread.php?s=&threadid=93860)
You will notice that while the model does recognize the underlying structures, the main idea behind the construction is maintaining the mesh flow.
And some final links:
Edgeloops ala Wings3d (http://pub161.ezboard.com/fnendowingsmiraifrm3.showMessage?topicID=135.topic)
Subdivision Modeling page (http://maxrovat.sns.hu/subdiv/)
I hope that helps. And should anyone seen an error that I made please correct me.
just to add something
10-14-2003, 05:46 AM
thanks for the all the info
01-16-2006, 08:00 AM
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