On 04/01/2011 01:32 PM, Trevor G Quayle wrote:
>>>
>>
>> OK ... so here's what I've come up with and it seems to work.
>>
>> #declare Intensity = function (LD,FD) { 1/(2/((1+(LD/FD))*(1+(LD/FD)))) };
>>
>>   From your example I used LD=2400 and FD=4.5 and get 142756 and some
>> change ;-) ... If I missed something feel free to set me straight as I'd
>> like to include this in [3.4.7.9] along with a small narrative.
>>
>> Jim
>
> That's exactly it.  However I would maybe modify it slightly for presentation.
> You can simplify by removing the double reciprocal (just invert the original
> equation).  Also, this is true for fade_power of 2, I would leave fade_power as
> part of it for completeness and to avoid confusion:
>
> #declare Intensity = function (LD,FD) {pow(1+(LD/FD),FP)/2};

LOL ... thanks fer makin' it purdy ;-)

>
> Also I would perhaps call it 'intensity multiplier' or similar.  If you want a
> base intensity of 2, you would multiply this factor by 2, etc.
>
> -tgq
>
When you get a second I'd appreciate a little QA:
http://wiki.povray.org/content/Documentation:Reference_Section_4.4#Light_Fading

Thanks :-)

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Jim Holsenback <jho### [at] povrayorg> wrote:
> On 04/01/2011 01:32 PM, Trevor G Quayle wrote:
> >
> > Also I would perhaps call it 'intensity multiplier' or similar.  If you want a
> > base intensity of 2, you would multiply this factor by 2, etc.
> >
> > -tgq
> >
> When you get a second I'd appreciate a little QA:
> http://wiki.povray.org/content/Documentation:Reference_Section_4.4#Light_Fading
>
> Thanks :-)

I think the two paragraphs following the graph need to be expanded somewhat or
the ideas better explained.

A few items:
"First, when Fade_Distance is larger than one, the light intensity at distances
smaller than Fade_Distance actually increases."
Actually this is true for any fade_distance, even when it is smaller than one.

"This is necessary to get the light source color if the distance traveled equals
Fade_Distance."
This isn't really necessary, as the function *could* have been set up the
regular way with 1 instead of 2 in the numerator (as it is for material
attenuation).  I believe it was set up the way it is so that one could set the
fade distance and know that at the fade_distance the light value would equal the
set intensity (a=1).  Meant to somewhat simplify it.

This is the way I had always treated it before until recently.  Now I am seeing
how it doesn't follow a very good inverse-squared relationship over
fade_distance and somwhat beyond if it is used this way.

The way I have come to use it now is to recognize that the function does break
down to be very close to inverse squared as the distance from fade_distance gets
significantly larger.  I think that perhaps this concept should be separated and
explained, as this is the purpose of the example code you have.
If I can find some time in the next few days I will try to consider some wording
for you if you don't come up with something in the meantime.

Also, as proof-reading note, don't use i.e. when you mean e.g.  I.e. means "that
is" and should be used to clarify a general statement that has a specific
meaning, and should not be used in place of e.g. "for example".  In the case
here "i.e.: the size of the light itself" I believe this should be e.g. as it is
one good (and appropriate) example of a value you could choose, but certainly
not the only one.

Sorry if I got a bit too carried away on you, no offense is intended, I have to
review reports for peers at work and for my wife at home, so I tend to get
carried away when doing this.

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On 04/01/2011 06:10 PM, Trevor G Quayle wrote:
> Jim Holsenback<jho### [at] povrayorg>  wrote:
>> On 04/01/2011 01:32 PM, Trevor G Quayle wrote:
>>>
>>> Also I would perhaps call it 'intensity multiplier' or similar.  If you want a
>>> base intensity of 2, you would multiply this factor by 2, etc.
>>>
>>> -tgq
>>>
>> When you get a second I'd appreciate a little QA:
>> http://wiki.povray.org/content/Documentation:Reference_Section_4.4#Light_Fading
>>
>> Thanks :-)
>
> I think the two paragraphs following the graph need to be expanded somewhat or
> the ideas better explained.

yep ... I tried to punch it up a bit and was hoping that you'd offer 
some insight.

>
> A few items:
<snip> ... I can work with what you posted here!

> Sorry if I got a bit too carried away on you, no offense is intended

no worries Trevor ... if it makes the docs better, ego's shouldn't be 
getting in the way ... I'm good to go. You've been a BIG help!

Cheers

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About the sculpting part of this discussion, Here's a very nic tutorial about
blender "sculpting" without adding geometry but directly painting the bump map:

http://www.blendernation.com/2011/03/31/tutorial-glsl-bump-painting/

Of course the final part where he consolidates everything into a Normal map is
not usable for POV-Ray.

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Also,
about the image, The plant adds a lot, wouldn't it be even nicer with more
backside diffuse (translucency) or even double_illuminate?

For the flower pot, temporarily switching media off and tweaking the brilliance
so that light bleeds a little deeper into shaded parts could make a quite
realistic terra cotta.

Is the downards light over the statue excluded from media? this looks a little
odd compared to the light entering the room which has a lot.

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On 04/01/2011 06:10 PM, Trevor G Quayle wrote:
> If I can find some time in the next few days I will try to consider some wording
> for you if you don't come up with something in the meantime.

Take two:
http://wiki.povray.org/content/Documentation:Reference_Section_4.4#Light_Fading

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On 04/02/2011 07:00 AM, Mr wrote:
> Also,
> about the image, The plant adds a lot, wouldn't it be even nicer with more
> backside diffuse (translucency) or even double_illuminate?
>
> For the flower pot, temporarily switching media off and tweaking the brilliance
> so that light bleeds a little deeper into shaded parts could make a quite
> realistic terra cotta.
>
> Is the downards light over the statue excluded from media? this looks a little
> odd compared to the light entering the room which has a lot.
>
>
All good points, that I'll try to work into the final version ... just 
wanted to get the docs squared away 1st ... business before pleasure right!

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Am 01.04.2011 13:34, schrieb Jim Holsenback:

> As far as fade_distance ... I'm still investigating but I think the
> nugget here is what Christoph said:
>
> "As I already mentioned, the key is not the fade_power, but the
> fade_distance. Sufficiently far away from the light source - relative to
> fade_distance (or, in other words, with sufficiently small fade_distance
> relative to the scene dimensions) - the formula gets arbitrarily close
> to 1/x2. "
>
> I've been using:
> #declare LightDist = vlength(LightPos);
>
> as my value for fade_distance, Which is WRONG ... I want a smaller value
> for that and up the intensity of the light source to compensate ...
> @Christoph: Did I get that right?

Yup. For area lights, I typically use half the area light's size as 
fade_distance; for point lights I pick some distance that might be a 
reasonable radius of the light source (e.g. radius of a light bulb).

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On 03/28/2011 10:26 AM, Jim Holsenback wrote:
> This scene was fun ... The Moai came from the AIM Shape Repository, but
> it was of fairly low quality. When I first brought it into my scene you
> could visibly see the triangles, then I roughed him up a bit with a
> fairly aggressive agate pattern. The scattering media turned out cool as
> well.

Here's another version after playing around with the lighting and 
composition.

Jim

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Attachments:
Download 'moai.png' (367 KB)

Preview of image 'moai.png'

On 05/04/2011 8:48 PM, Jim Holsenback wrote:

>
> Here's another version after playing around with the lighting and
> composition.
>

Getting better and better.
Maybe a little more "normal" in the floor reflection. Not too much though.

-- 
Regards
     Stephen

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