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From: Jaro
Subject: Glass and wood problem
Date: 15 Aug 2009 14:45:01
Message: <web.4a870154d021a0e025187c730@news.povray.org>
Hi all!
I'm new to pov-ray and I noticed strange thing about glass. It's full of grey
1px dots, and I do not know why and how to remove this...
http://img37.imageshack.us/img37/994/error2l.png
Here is scene file: http://pokazywarka.pl/pov/ , just render 3 frames. On my pc
first looks ok, but it is without wooden table under glass, third one is grainy
only on sides of this piece of glass.
Sorry for my bad English and please, help me.


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From: StephenS
Subject: Re: Glass and wood problem
Date: 15 Aug 2009 15:25:00
Message: <web.4a870b80717daab85b50486a0@news.povray.org>
"Jaro" <nomail@nomail> wrote:
> Hi all!
> I'm new to pov-ray and I noticed strange thing about glass. It's full of grey
> 1px dots, and I do not know why and how to remove this...
> http://img37.imageshack.us/img37/994/error2l.png
> Here is scene file: http://pokazywarka.pl/pov/ , just render 3 frames. On my pc
> first looks ok, but it is without wooden table under glass, third one is grainy
> only on sides of this piece of glass.
> Sorry for my bad English and please, help me.

Try increasing max_trace_level from 5 to 11

global_settings {
    max_trace_level 11
}

Stephen S


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From: Stephen
Subject: Re: Glass and wood problem
Date: 15 Aug 2009 15:55:58
Message: <ka4e851ldlb3bj2v56rrjesv2ughk6ho5f@4ax.com>
On Sat, 15 Aug 2009 15:24:48 EDT, "StephenS" <nomail@nomail> wrote:


>Try increasing max_trace_level from 5 to 11
>
>global_settings {
>    max_trace_level 11
>}
>

I think that there is also a coincident surface as well. Increase the height of
the box by adding a tiny bit to the translate like    translate y*7.51
You don't need a merge unless you are going to add something else to the box and
want to get rid of the internal structure.

When you look at the Statistics in the message window you will see Max Level:
5/5.
That means that the maximum of 5 has been reached. I changed max_trace_level to
25 then PovRay reports Max Level: 11/25

So you can use any value above 10 in your scene.

Render Statistics
Image Resolution 512 x 384

Pixels:           196608   Samples:               0   Smpls/Pxl: 0.00
Rays:            2371030   Saved:                 0   Max Level: 5/5

-- 

Regards
     Stephen


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From: clipka
Subject: Re: Glass and wood problem
Date: 15 Aug 2009 16:01:06
Message: <4a871402$1@news.povray.org>
Jaro schrieb:
> I'm new to pov-ray and I noticed strange thing about glass. It's full of grey
> 1px dots, and I do not know why and how to remove this...
> http://img37.imageshack.us/img37/994/error2l.png
> Here is scene file: http://pokazywarka.pl/pov/ , just render 3 frames. On my pc
> first looks ok, but it is without wooden table under glass, third one is grainy
> only on sides of this piece of glass.

Your glass surface is resting directly on the wooden table, at y=7.5; 
what you experience here is commonly referred to as "coincident surface 
problem": POV-Ray is not particularly good at dealing with surfaces of 
two objects just exactly touching each other, and gets the measles (sort 
of), because it just can't make up its mind which surface is "nearer" to 
the observer.

Translate the glass plate by y*7.5001 instead of y*7.5, and you should 
be fine.


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From: Jaro
Subject: Re: Glass and wood problem
Date: 15 Aug 2009 17:05:00
Message: <web.4a872203717daab825187c730@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Jaro schrieb:
> > I'm new to pov-ray and I noticed strange thing about glass. It's full of grey
> > 1px dots, and I do not know why and how to remove this...
> > http://img37.imageshack.us/img37/994/error2l.png
> > Here is scene file: http://pokazywarka.pl/pov/ , just render 3 frames. On my pc
> > first looks ok, but it is without wooden table under glass, third one is grainy
> > only on sides of this piece of glass.
>
> Your glass surface is resting directly on the wooden table, at y=7.5;
> what you experience here is commonly referred to as "coincident surface
> problem": POV-Ray is not particularly good at dealing with surfaces of
> two objects just exactly touching each other, and gets the measles (sort
> of), because it just can't make up its mind which surface is "nearer" to
> the observer.
>
> Translate the glass plate by y*7.5001 instead of y*7.5, and you should
> be fine.

Thank you all very much :) I was not expecting "coincident surface problem" to
show on top and on sides of glass.
It's only a part of scene, I need to use merge, because I'm adding some elemets
there, and glass is transparent.


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From: clipka
Subject: Re: Glass and wood problem
Date: 15 Aug 2009 19:11:52
Message: <4a8740b8$1@news.povray.org>
Jaro schrieb:
> Thank you all very much :) I was not expecting "coincident surface problem" to
> show on top and on sides of glass.

The reason behind this is that it's not really on top and sides of the 
glass, but instead is the refracted image of coincident-surface dots 
appearing on the bottom.


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