Margus Ramst <mar### [at] peakeduee> wrote in message news:371bb1cb.0@news.povray.org...
>
> First, remember that the cirumference of an ellipse is not 2*pi*r. An
> approximation is 2*pi*sqrt[(a^2+b^2)/2] where a and b are lengths of major
> and minor axes.
>
> The other value you want - I haven't got right now. But why not just do
> this: use the Superpatch's trace() function; trace a line from the centre
> straight down. You can now get the radius for the current angle.
>
> Basically like this:
>
> #declare Ellipse=sphere{0,1 scale <.25,1,.25> rotate z*clock*360}
> #declare Rad=trace(Ellipse,0,-y).y;
>
> At least I think this should work.

Thanks Margus,

I was hoping to avoid using the superpatch....I'm not at all familiar with the trace
function. But I will give it a go and see how I get on.

Andy

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