TITLE: About sphere equation $z = a+bx+cy+dx^2 +ey^2$
QUESTION [1 upvotes]: I'm trying to fit a sphere from points. I tried a first way to estimate the sphere but I'm not satisfied.
I saw in an article a way to get a best fitting sphere from the equation :
$z = a+bx+cy+dx^2 +ey^2$
Now, I have $a,b,c,d$ and $e$ values but I don't know what is the center of the sphere, radius ...
Do you have some explanation about this equation ?
Thank you.

REPLY [2 votes]: This is an extract (translated) from pp.17-18 http://fr.scribd.com/doc/14819165/Regressions-coniques-quadriques-circulaire-spherique
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