Pictures made for some tests in our company with a modified version of
MegaPov which can use real light distribution data.

Martin Hellwig
DIAL GmbH
http://www.dial.de

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Attachments:
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Preview of image 'Room.jpg'

Hello,

Light is an interesting subject, but it's not too easy for me to see what
this is all about.. I've been at your webpage too.. Could you explain what
your version does, that MegaPOV cannot do on it's own?

Regards,
Hugo

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> Light is an interesting subject, but it's not too easy for me to see what
> this is all about.. I've been at your webpage too.. Could you explain what
> your version does, that MegaPOV cannot do on it's own?

Hello,
the difference of our modified test version of povray is the way in which
light leaves a luminaire. Original POVRay or MegaPOV use simple mathematical
descriptions like cones. But for most luminaires there exists data files
which describe
the real light distribution of a luminaire. A scene should looks more
realistic with
realistic light distributions.
I included another picture of a spotlight which extremly shows what i mean.
Try
to build the light patterns on the wall with POVRay lightsources.

Martin Hellwig
DIAL GmbH
http://www.dial.de

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Attachments:
Download 'LDTPatternsOnWall.jpg' (43 KB)

Preview of image 'LDTPatternsOnWall.jpg'

Martin Hellwig wrote:
> I included another picture of a spotlight which extremly shows
> what i mean.  Try to build the light patterns on the wall with
> POVRay lightsources.

Can your mod of POV make a low-watt lightbulb, that's on, with
the camera pointing at the lightsource, and it be realistic?
(i.e. the tungsten filament glowing and producing the light)
If it can...why can't POV do that?

-- 
Tim Cook
http://empyrean.scifi-fantasy.com
mirror: http://personal.lig.bellsouth.net/lig/z/9/z993126

-----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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> Can your mod of POV make a low-watt lightbulb, that's on, with
> the camera pointing at the lightsource, and it be realistic?
> (i.e. the tungsten filament glowing and producing the light)
> If it can...why can't POV do that?

No, actually not, because the data for a light source are not
measured that fine to display the effect you want. Thats a
common problem when doing lighting calculations. First,
there is no common data format available to describe this
task and it would be also difficult to do the real measurement.

Martin Hellwig
DIAL GmbH
http://www.dial.de

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in news:3ce27ec7@news.povray.org Martin Hellwig wrote:

> But for most luminaires there exists data files
> which describe the real light distribution of a luminaire.

You mean it reads IESNA LM-63 photometric data files or someting alike and 
control the lightsource with that? 

Ingo

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On Wed, 15 May 2002 17:30:10 +0200, "Martin Hellwig" <hel### [at] dialde>
wrote:

>I included another picture of a spotlight which extremly shows what i mean.
>Try
>to build the light patterns on the wall with POVRay lightsources.

I'm very interested in these images of yours. I'm very interested in
anything that makes POV closer to "real-world behavior", and I've been
hoping that someone would do something like this for quite a while.

Does your software account for color temperature, as well as the light
distribution pattern?

I hope you will eventually release your patch. I couldn't find mention
of it on your web site. It would be great to add something like this
to POV 3.5, when it's available in source code.


Later,
Glen

7no### [at] ezwvcom     (Remove the numeral "7")

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> You mean it reads IESNA LM-63 photometric data files or someting alike and
> control the lightsource with that?

Yes, but only indirect.

The scenes are exported from a developer version of our
programme DIALux which does lighting calculations. This
software naturally can read the most important european
and american formats like IES and EULUMDAT.

The export function in our programm writes equal but
format independent information to the POVRay scene
file. So any format can be transformed to this form.

Hope this helps.

Martin Hellwig
DIAL GmbH
http://www.dial.de

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> Does your software account for color temperature, as well as the light
> distribution pattern?
>
> I hope you will eventually release your patch. I couldn't find mention
> of it on your web site. It would be great to add something like this
> to POV 3.5, when it's available in source code.

Hi,

I will think about posting the patch, but i can't decide it
on my own. Since it is only a quick but not so dirty hack
it has to be refined and tested. By now it is a very little
patch, an estimated 100 lines of code added. So i
asked to myself why that wasn't already in there :)

Color temperature is not supported.

Martin Hellwig
DIAL GmbH
http://www.dial.de

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Martin Hellwig wrote:
> I will think about posting the patch, but i can't decide it
> on my own. Since it is only a quick but not so dirty hack
> it has to be refined and tested. By now it is a very little
> patch, an estimated 100 lines of code added. So i
> asked to myself why that wasn't already in there :)

  Because only a few people like you have both the knowledge about LDT and 
POV-Ray? :) 

  As Glenn said, it will be really nice to have it on the next MegaPOV 
incarnation, based on 3.5. I hope you will release it... as I see it, 
radiosity could perhaps do this, but you will need to model extremely well 
the geometry and reflectance of surfaces, and use very high qualitity rad 
settings. Using rad in adittion to light distribution tables, could improve 
the ligthing with low/mid rad quality. 

> Color temperature is not supported.

  That's not a big problem, because it could be coded into POV-Ray script 
(converting Kelvin to RGB, or averaging spectrum samples as in my recent 
macros).
 
-- 
Jaime Vives Piqueres

La Persistencia de la Ignorancia
http://www.ignorancia.org

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