POV-Ray : Newsgroups : povray.general : Inverse sphere? Server Time: 27 Jun 2019 04:26:09 GMT
  Inverse sphere? (Message 1 to 6 of 6)  
From: Mike Horvath
Subject: Inverse sphere?
Date: 28 May 2019 18:52:39
Message: <5ced8377$1@news.povray.org>
This tutorial about radiosity:

http://wiki.povray.org/content/HowTo:Use_radiosity#Step_5:_Find_Your_Error_Bound

says:

 > Sometimes radiosity can cause artifacts, one of the most common 
causes of artifacts is infinite radiosity rays. A good rule is to place 
any radiosity scene inside a large inverse sphere to avoid any ray 
colliding with the background or sky_sphere.

What is an inverse sphere? And how is it useful/beneficial in this 
situation? Thanks.


Michael


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From: Mike Horvath
Subject: Re: Inverse sphere?
Date: 28 May 2019 18:56:56
Message: <5ced8478$1@news.povray.org>
On 5/28/2019 2:52 PM, Mike Horvath wrote:
> This tutorial about radiosity:
> 
> http://wiki.povray.org/content/HowTo:Use_radiosity#Step_5:_Find_Your_Error_Bound 
> 
> 
> says:
> 
>  > Sometimes radiosity can cause artifacts, one of the most common 
> causes of artifacts is infinite radiosity rays. A good rule is to place 
> any radiosity scene inside a large inverse sphere to avoid any ray 
> colliding with the background or sky_sphere.
> 
> What is an inverse sphere? And how is it useful/beneficial in this 
> situation? Thanks.
> 
> 
> Michael


Oops! That link should be:

http://wiki.povray.org/content/HowTo:Use_radiosity#Artifacts


Michael


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From: Bald Eagle
Subject: Re: Inverse sphere?
Date: 28 May 2019 20:50:01
Message: <web.5ced9de9603a316d4eec112d0@news.povray.org>
Mike Horvath <mik### [at] gmailcom> wrote:

> What is an inverse sphere?

It's a spherical cavity inside the [solid] infinite POV-Ray space.

A solid sphere's inverse.


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From: Le Forgeron
Subject: Re: Inverse sphere?
Date: 29 May 2019 05:48:18
Message: <5cee1d22$1@news.povray.org>
Le 28/05/2019 à 22:45, Bald Eagle a écrit :
> 
> Mike Horvath <mik### [at] gmailcom> wrote:
> 
>> What is an inverse sphere?
> 
> It's a spherical cavity inside the [solid] infinite POV-Ray space.
> 
> A solid sphere's inverse.
> 

and for the code oriented, it looks like:

sphere { 0, 1e+5 inverse  ...


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From: Thomas de Groot
Subject: Re: Inverse sphere?
Date: 29 May 2019 06:33:28
Message: <5cee27b8$1@news.povray.org>
On 29-5-2019 7:48, Le_Forgeron wrote:
> Le 28/05/2019 à 22:45, Bald Eagle a écrit :
>>
>> Mike Horvath <mik### [at] gmailcom> wrote:
>>
>>> What is an inverse sphere?
>>
>> It's a spherical cavity inside the [solid] infinite POV-Ray space.
>>
>> A solid sphere's inverse.
>>
> 
> and for the code oriented, it looks like:
> 
> sphere { 0, 1e+5 inverse  ...
> 

alternatively, although less elegant: sphere {0, 1e+5 hollow ...}  gives 
the same result.

-- 
Thomas


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From: Alain
Subject: Re: Inverse sphere?
Date: 30 May 2019 15:34:18
Message: <5ceff7fa$1@news.povray.org>
Le 19-05-28 à 14:52, Mike Horvath a écrit :
> This tutorial about radiosity:
> 
> http://wiki.povray.org/content/HowTo:Use_radiosity#Step_5:_Find_Your_Error_Bound 
> 
> 
> says:
> 
>  > Sometimes radiosity can cause artifacts, one of the most common 
> causes of artifacts is infinite radiosity rays. A good rule is to place 
> any radiosity scene inside a large inverse sphere to avoid any ray 
> colliding with the background or sky_sphere.
> 
> What is an inverse sphere? And how is it useful/beneficial in this 
> situation? Thanks.
> 
> 
> Michael

It can be a sphere with the «inverse» attribute, or a sphere with the 
hollow attribute.

The use of inverse or hollow is to allow the use of fog and media.

In my experience, I have never encountered any case where infinite rays 
have caused any artifacts.

My guess is it's a leftover from the early radiosity implementation that 
still had a max_distance setting that imposed a cutoff distance when 
testing for radiosity samples.


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