michael mcknight <nes### [at] ouedu> wrote:

> i posted earlier saying that i get an error in julia fractals sometimes
that
> looks like parts of them have been randomly sliced up.  i got a reply,
which
> i was most grateful for, saying that the putting the camera inside the
> bounding sphere of the julia fractal was causing the error.
unfortunately,
> when i moved it back to 20 units, i still get the error.  does anyone one
> know why?  thanks in advance.  here's my code.
>
> camera{
>   location -20*z
>   angle 6
> }
>
> light_source{
>   <-5,0,-20>
>   color rgb 1.3
> }
>
>
ia_fractal{ 
>   <-1.154166666666666, -0.25, 0, 0>
>   max_iteration 10 
>   quaternion
>   sqr   
>   precision 100
>   pigment{rgb <1,.3,.3>}
>   rotate<0,80,0>
> }
> 
> michael
> 

First: Thanks for the e-mail
          (you could have put it in the NG, though,
          I usually check for answers for a few days at least).

Now, when it comes to fractals
I just _have_ to get my (less than) 2 cents worth into the discussion ;)

IMHO the most probable cause of this is the distance estimator used
for quaternion fractals. As the name says, it's an estimate, and - according
to Peitgen's and Saupe's "Science Of Fractal Images" - really accurate
only for high iteration values.

Besides, I'm missing a factor of 0.5 in the implementation of the formula,
making the estimates twice as big as they should be (provided I'm right).

-- 
Gerald
ger### [at] aonat

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