The fresh wear on the edges is a great effect, BB.  :-)  The formula seems to be measuring eccentricity well but not distinguishing between convex (lots of wear) and concave (little wear).

Yes. I confess my reputation at math exceeds my actual skills. It is only that most people are so disinterested in practice with math that it seems I understand it well. I actually don't - I just practice a lot. I have had almost no instruction in multi-dimensional calculus and so how you go about detecting concave versus convex functions is barely above a mystery to me. I'm hoping that the thread I referenced above, wherein bluearms did the work, turns out to be correct work and I can just use it. I can copy/paste a formula as well as the next monkey, I suppose.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)