I'm trying to build a circular parabolic dish solar concentrator. So
far I've designed a simple hub to which I'll attach radial ribs. These
ribs will support reflective "petals" and an outer support ring.

I know that the general formula for a parabola is:

(x - h) ^ 2 = 4 * a * (y - k), where

(h,k) are the coordinates of the vertex and
a is the distance from the vertex to the focus and the distance from
the vertex to the directrix (and one-fourth the length of the latus
rectum).

What I need is an algebraic expression representing the distance along
the parabola from the vertex to any point (x,y) on the parabola so I
can lay out the shape of a petal for cutting from flat stock.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/solar.html