POV-Ray : Newsgroups : povray.general : fade_power documentation question Server Time
27 Dec 2024 22:18:07 EST (-0500)
  fade_power documentation question (Message 1 to 5 of 5)  
From: Tim Cook
Subject: fade_power documentation question
Date: 13 Dec 2005 05:30:56
Message: <439ea2e0$1@news.povray.org>
The documentation for POV 3.5 says "For realistic effects a fade power 
of 1 to 2 should be used.", then "If you set fade_power in the interior 
of an object at 1000 or above, a realistic exponential attenuation 
function will be used"...this is confusing.  Which is the realistic 
value, 1..2, or 1000+?

-- 
Tim Cook
http://home.bellsouth.net/p/PWP-empyrean

-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------


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From: Warp
Subject: Re: fade_power documentation question
Date: 13 Dec 2005 06:01:44
Message: <439eaa18@news.povray.org>
Tim Cook <z99### [at] bellsouthnet> wrote:
> The documentation for POV 3.5 says "For realistic effects a fade power 
> of 1 to 2 should be used.", then "If you set fade_power in the interior 
> of an object at 1000 or above, a realistic exponential attenuation 
> function will be used"...this is confusing.  Which is the realistic 
> value, 1..2, or 1000+?

  1000 is not a true value. It's a hack. It just turns a different
algorithm on.
  A keyword should have been used instead, but for historic reasons
the hack still seems to be there.

-- 
                                                          - Warp


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From: Frango com Nata
Subject: Re: fade_power documentation question
Date: 13 Dec 2005 07:10:01
Message: <web.439eb9486b228396d3eb7f560@news.povray.org>
I think the most logical goal of a light source's fade settings is to model
its light's attenuation due to its energy spreading on ever-expanding
spherical wavefronts, which requires a fade_power of 2, since this effect
makes the light's intensity fall off proportionally to the inverse of the
distance travelled squared, the successive spheres' area being proportional
to the squares of their radii. However, this purpose doesn't make sense for
an interior fade_power, as it can't take the light's location into account,
so the feature should be used as a quick way to simulate light absorption
(without resorting to the fine calculations of media), which causes light
intensity to decrease exponentially, the way a fade_power 1000 or greater
sets up.


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From: Trevor G Quayle
Subject: Re: fade_power documentation question
Date: 13 Dec 2005 09:00:01
Message: <web.439ed3526b2283966c4803960@news.povray.org>
Tim Cook <z99### [at] bellsouthnet> wrote:
> The documentation for POV 3.5 says "For realistic effects a fade power
> of 1 to 2 should be used.", then "If you set fade_power in the interior
> of an object at 1000 or above, a realistic exponential attenuation
> function will be used"...this is confusing.  Which is the realistic
> value, 1..2, or 1000+?
>

The answer is both.  If you reread it, you'l see for the main fade function,
a value of 1-2 gives realistic results.  However, if you set it to 1000 or
above, a different function is used.


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From: Darren New
Subject: Re: fade_power documentation question
Date: 13 Dec 2005 11:48:08
Message: <439efb48$1@news.povray.org>
Trevor G Quayle wrote:
>>function will be used"...this is confusing.  Which is the realistic
> above, a different function is used.

Sounds like you should add "instead" after "used" in the documentaton. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
    Sabotage? Communist conspiracy? Or just
    Microsoft again? Only time will tell.


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