Wasn't it JRG who wrote:
>Evalute 1,10,0.99 leads to strange results and slow renderings (I got 400
>max_gradient ?!)
>Shouldn't  1,1,0.99 be a good starting point? (1,10,0.99 is suggested by the
>doc).

The MegaPOV "eval" defaults to 1,1.2,0.99 and that seemed to work pretty
well in the majority of cases.

In 3.5b1 you can sometimes get a reasonable compromise by specifying
*both* a max_gradient and an evaluate. By setting a low max_gradient and
a high evaluate you can sometimes get a grotty copy of the image to
render reasonably quickly and still give good evaluate information in
the messages pane.

>Sorry if this sounds like a silly question: what should isosurface speed
>performances be campared to MegaPov's? I'm asking this because Warp's torus
>(see image posted in p-b-i) takes more to render in POV 3.5.

Most of the time 3.5b1 is a little faster, but occasionally, for some
parametric isosurfaces, 3.5b1 is *phenomenally* slower.

I'm in the process of rewriting my Isosurface Tutorial scenes using the
3.5b1 syntax, and I've had to perform a considerable amount of
optimisation to render the Steiner Cross Cup in order to get the
rendering time under two hours for a 320x240 image without
antialiassing. 

At the current stage of tweaking, POV 3.5b1 takes 1h 36m 44s and MegaPOV
takes 1m 8s. That's a speed difference of 8500%. 3.5b1 is still showing
a few holes, so I guess it needs a slightly higher max_gradient and will
take even longer to render. (Evaluate isn't available for parametric
isosurfaces, and I don't know how to defferentiate the Steiner Cross
Cup, so I'm having to find a reasonable max_gradient by trial and
error.)

POV 3.5b1, Win 98se, AMD K6-2 500, 128Mb.

-- 
Mike Williams
Gentleman of Leisure

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