>The camera or the end of the direction vector is inside the bounding
>sphere of the fractal. Modify your camera statement to:
>
>camera { location -5*z angle 30 }

well, my reply got lengthy, so i'm putting the the modified scene at the
top.  i moved the camera farther back than (i would think) any bouding
sphere would go, and brought the light back too, just in case.  it still
gives me strange noise on my machine.


camera{
  location -20*z
  angle 6
}

light_source{
  <-5,0,-20>
  color rgb 1.3
}

julia_fractal{ 
  <-1.154166666666666, -0.25, 0, 0>
  max_iteration 10 
  quaternion
  sqr   
  precision 100
  pigment{rgb <1,.3,.3>}
  rotate<0,80,0>
}




>Also, precision 2000 is overkill, I have rarely needed
>more than 100.

  i was rendering this one zoomed in at 20 iterations before so i needed the accuracy
then; i didn't bother to change the precision because it doesn't seem to affect
perfomance - i toned it down in the scene i included this time though.  you'd be
amazed how a low accuracy looks if the set animated.  it may seem just fine in a
still, but the striation is painfully obvious once it starts to move.

> Be warned that at iteration levels above 6 you should
>expect a lot of fractal dust.

i tend to avoid those, i like the way a more contiguous shape looks.

>Lastly, I suggest giving the julia a
>no_shadow statement for test renders because you can make out the
>shape better this way and it's also faster.
>
>Enjoy!
>

thanks, i'll keep that in mind. - some of my test renders are deathly slow.  keep this
with shadows though, it makes the error easier to see.  (also why i offset the light
source.)

>BTW have you been able to grasp how the different parameters, more
>precisely the two vectors, affect the shape of the fractal?
>

  a bit - if you keep the second two values in the parameter vector at zero, the first
two give you 2d julia sets at z=0 (povspace) which are the same as regular old 2d
julia sets with the same 2 parameters.  i don't have
 a very good general feel for how changing a parameter will affect the
shape - but i found a program called quat that helps a lot.  it's a
standalone quaternion generator.  the one thing you have to remember is that
to convert the parameters over to povray, you have to use the negative of
the 1st and 3rd parameters in quat.  it's at
http://wwwcip.rus.uni-stuttgart.de/~phy11733/quat_e.html
  i've only messed with the 4d normal vector once, so i don't really have a
feel for it at all.

  does anyone know why the fourth component of the 4d normal can't be zero?

Michael

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