POV-Ray : Newsgroups : povray.general : Artifacts when tracing somewhat high degree poly Server Time
22 Mar 2023 17:45:25 EDT (-0400)
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From: Adrien
Subject: Re: Artifacts when tracing somewhat high degree poly
Date: 6 Dec 2022 14:05:00
Message: <web.638f91e399cae61a75a7ea2178e7deb4@news.povray.org>
"jr" <cre### [at] gmailcom> wrote:
> hi,
>
> "Adrien" <nomail@nomail> wrote:
> > > ...
> > Fantastic, thanks a lot ! ...
>
> great.  (and, pleasure)
>
>
> > ... Thought I get an error from the +ac0.99 option, I'll try to figure out why.
>
> you do use a v3.8?
>
>
> regards, jr.

No 3.7, I had compiled 3.8 a while ago but it broke when I upgraded my distro.
Will compile again.


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From: jr
Subject: Re: Artifacts when tracing somewhat high degree poly
Date: 7 Dec 2022 01:50:00
Message: <web.6390378099cae61ac0ce110b6cde94f1@news.povray.org>
hi,

"Adrien" <nomail@nomail> wrote:
> No 3.7, I had compiled 3.8 a while ago but it broke when I upgraded my distro.
> Will compile again.

<https://github.com/POV-Ray/povray/tags>


regards, jr.


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From: Thomas de Groot
Subject: Re: Artifacts when tracing somewhat high degree poly
Date: 8 Dec 2022 08:06:07
Message: <6391e13f@news.povray.org>
Op 6-12-2022 om 10:03 schreef Adrien:
> Hi,
> 
> I'm trying to use Povray to plot a surface defined by a polynomial equation
> spitted out by an auxiliary program. However, whenever the degree of that
> polynomial is 10 or more I get a bunch of artifacts/black dots. Is there a way
> to fix that ? Either directly in Povray, or in the auxiliary program ?
> 

wrapping up my experiments, I think I got a acceptable solution for your 
problem. Use the following additions/changes to your code (see attached 
image):

//=====================================================
//+w640 +h640 +am3 +a0.01 +ac0.99 +r3 +bm2 +bs8

#version 3.8;

global_settings {
   assumed_gamma 1.0
   radiosity {
     pretrace_start 16/max(image_width,image_height)
     pretrace_end   4/max(image_width,image_height)
     minimum_reuse  4/(max(image_width,image_height)-0.05)
     #if (Stochastic)
       count 10
     #else
       count 50, 1000
     #end
     nearest_count 20, 3
     error_bound 1
     recursion_limit 2
     low_error_factor .3
     gray_threshold 0.0
     //minimum_reuse 0.015
     maximum_reuse 0.1
     brightness 1

     adc_bailout 0.01/2
     normal off
     media off
     always_sample off
     //max_sample 1.0
   }
}

light_source {
   2*<5, 10, -40>
   color White
   area_light <5, 0, 0>, <0, 0, 5>, 5, 5
   adaptive 2
   area_illumination on
   jitter
   circular
   orient
   /*fade_power 1
   fade_distance 30*/
}
//=====================================================

All the rest is unchanged. Whether radiosity is "necessary" here is a 
matter of taste.

Very interesting poly btw...

-- 
Thomas


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Attachments:
Download 'adrien_poly.png' (176 KB)

Preview of image 'adrien_poly.png'
adrien_poly.png


 

From: Thomas de Groot
Subject: Re: Artifacts when tracing somewhat high degree poly
Date: 8 Dec 2022 08:08:49
Message: <6391e1e1$1@news.povray.org>
I see I have forgotten to add:

#declare Stochastic = on;

before the global_settings block. Sorry.

-- 
Thomas


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From: Alain Martel
Subject: Re: Artifacts when tracing somewhat high degree poly
Date: 8 Dec 2022 13:56:18
Message: <63923352$1@news.povray.org>
Le 2022-12-08 à 08:06, Thomas de Groot a écrit :
light_source {
   2*<5, 10, -40>
   color White
   area_light <5, 0, 0>, <0, 0, 5>, 5, 5
   adaptive 2
   area_illumination on
   jitter
   circular
   orient
   /*fade_power 1
   fade_distance 30*/
}

Using adaptive 2 with that area_light is exactly the same as not using 
it at all as the starting grid is 5x5.
For adaptive 2 to have any benefit, the grid need to be strictly larger 
than 5 in at least one direction. So,
  area_light <5, 0, 0>, <0, 0, 5>, 9, 9
or more.

Adaptive level, starting grid
	0		2x2
	1		3x3
	2		5x5
	3		9x9
Here is the formula to know the starting grid :
(adaptive level)^2 +1


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From: Thomas de Groot
Subject: Re: Artifacts when tracing somewhat high degree poly
Date: 9 Dec 2022 02:15:04
Message: <6392e078$1@news.povray.org>
Op 08/12/2022 om 19:56 schreef Alain Martel:
> Using adaptive 2 with that area_light is exactly the same as not using 
> it at all as the starting grid is 5x5.
> For adaptive 2 to have any benefit, the grid need to be strictly larger 
> than 5 in at least one direction. So,
>   area_light <5, 0, 0>, <0, 0, 5>, 9, 9
> or more.
> 
> Adaptive level, starting grid
>      0        2x2
>      1        3x3
>      2        5x5
>      3        9x9
> Here is the formula to know the starting grid :
> (adaptive level)^2 +1

Of course! My bad.

Thanks Alain. Always good to know someone is watching your back! ;-)

-- 
Thomas


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