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17 Aug 2024 08:23:54 EDT (-0400)
  Isosurface Tribulations (Message 1 to 3 of 3)  
From: banty
Subject: Isosurface Tribulations
Date: 12 Oct 2001 00:09:31
Message: <3BC66F2A.9EC18E8D@rapidnet.com>
I've been trying to aquaint myself with the isosurface functions in
PoV 3.5, but as I go through the tutorials I keep getting strange
results from the functions they tell me to input, results which don't
show up un the example pictures.  I also get black moire like patterns
in the surface of the rendered objects.
    Is this a bug or is it a difference in operators between Pov 3.5 and
mega pov?


A.D.B


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From: Christoph Hormann
Subject: Re: Isosurface Tribulations
Date: 12 Oct 2001 04:36:46
Message: <3BC6AB9D.2CE1D1B3@gmx.de>
banty wrote:
> 
>     I've been trying to aquaint myself with the isosurface functions in
> PoV 3.5, but as I go through the tutorials I keep getting strange
> results from the functions they tell me to input, results which don't
> show up un the example pictures.  I also get black moire like patterns
> in the surface of the rendered objects.
>     Is this a bug or is it a difference in operators between Pov 3.5 and
> mega pov?
> 

It's neither a bug nor a difference.  You have to specify a correct
max_gradient value like it is mentioned in the docs (section 3.4.4.7 and
6.5.4.5.3).  

If you are trying to render the functions in the 3.5 docs, make sure you
add a higher max_gradient than default for the later functions (it's also
mentioned in the text).

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/


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From: Mike Williams
Subject: Re: Isosurface Tribulations
Date: 12 Oct 2001 13:05:14
Message: <SKevfGA7fox7Ew+r@econym.demon.co.uk>
Wasn't it banty who wrote:
>    I've been trying to aquaint myself with the isosurface functions in
>PoV 3.5, but as I go through the tutorials I keep getting strange
>results from the functions they tell me to input, results which don't
>show up un the example pictures.  I also get black moire like patterns
>in the surface of the rendered objects.
>    Is this a bug or is it a difference in operators between Pov 3.5 and
>mega pov?

If you're trying to follow one of the web based tutorials that was
written for Megapov, then you'll probably need to specify a (higher)
max_gradient.

If you're trying to follow my Isosurface tutorial, 
        <http://www.econym.demon.co.uk/isotut/>
then I would expect it all to work. Let me know if you are having
trouble with my examples.

For the tutorial in the help docs, you need to spot the sneaky little
sentence that says "Note that i added 'max_gradient 4' to the isosurface
definition here, this will be explained later on." and continue to use
'max_gradient 4' in (most of) the subsequent scenes. On the other hand,
after rendering the scene that demonstrates "threshold 1" you'll need to
remember to remove that line before you get to function{ abs(x)-1 }.

-- 
Mike Williams
Gentleman of Leisure


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