AW: [Radiance-general] Infrared scene simulation

[Alexander Utz]

Hi Greg,

first of all thank you for the last mail. Meanwhile I made some first tests and what I saw till now
seems to be quite promising for my needs. Unfortunately I still have some problems understanding
and handling the glow-reflection material mix. Maybe you can help me with this. So here is what I have done:

       # amount of radiation energy depends on the object's temperature and emissivity
                                # BB at T=21°C
        void glow glow_e1
        0
        0
        4 135.13 135.13 135.13 100

        This is my basic glow. 135.13W/m2/sr is about the radiation of a Blackbody at 21°C. I
        mixed this with some material the way you showed me:

        void mixfunc l_col040_
                4 glow_e1 col040_ e_plastic materials/emissivity.cal
                0
                0

         So the fraction of total radiation of the mixture from the Blackbody's one is applied here.

I rendered my scene and iradiance pictures and created the falsecolor picture and the distribution
of irradiance looks quite as I expected. Only surfaces which are not illuminated by other glows
appear absolutely "black", i.e. irradiance of 0. So it seems to me I only see reflection but not
the radiation emitted by the surfaces themselves.

I thought I might have to increase the max range of the glow so I gave a maxrad value of 10000
instead of 100. The result was that the total iradiance of the whole scene was limited to a tiny
fraction of the original one and this confused me completely.

So can you please tell me what I'm doing wrong?

Thanks in advance and Best Regards

Alex


-----Ursprüngliche Nachricht-----
Von: Greg Ward [mailto:gward at lmi.net] 
Gesendet: Donnerstag, 4. Juni 2009 19:30
An: Alexander Utz
Cc: Radiance general discussion
Betreff: Re: [Radiance-general] Infrared scene simulation

Hi Axel,

Thanks for explaining your exact problem.  The documentation for  
Radiance is scattered and frequently application-specific.  Did you  
browse the "Seminars and Course Notes" section of:

	http://radsite.lbl.gov/radiance/refer/

Francesco Anselmo's Radiance wiki is also useful:

	http://www.bozzograo.net/radiancewiki/doku.php

Check out Axel Jacob's tutorials at:

	http://luminance.londonmet.ac.uk/learnix/docs.shtml

As for describing a mixture, you need to use the "mixfunc" type.   
Correcting what you gave in your e-mail:

> I calculated the total amount of energy emitted by a 300°K  
> blackbody as
> 146.305W/(sr m^2). So the material for my source becones
>
>      void light bright
>      0
>      0
>      3  48.77 48.77 48.77

Don't bother dividing the value up, just give it three times:

      void light bright
      0
      0
      3  146.305 146.305 146.305


>      void plastic brown
>      0
>      0
>      5  .2  .1  .1  0  0
>
>      brown glow brown_glow
>      0
>      0
>      4 100 100 100 100
>
>      brown_glow sphere BB
>      0
>      0
>      4  2  1  1.5  .125

Should be:

      void plastic brown
      0
      0
      5  .2  .1  .1  0  0

      void glow bit_of_glow
      0
      0
      4 100 100 100 100

	void mixfunc brown_glow
	4 brown bit_of_glow 0.5 .
	0
	0

      brown_glow sphere BB
      0
      0
      4  2  1  1.5  .125

--------
Note that I gave half of each, so their actual values will be reduced  
by 50%.  In some cases,  you may wish to double the parameters to  
compensate.

Cheers,
-Greg

> From: Alexander Utz <AlexanderUtz at web.de>
> Date: June 4, 2009 8:12:53 AM PDT
>
> Hi Greg,
>
> what I want to know is the distribution of Infrared Radioation in a  
> Test System
> for an infrared camera. So temperature of the objects in the scene  
> is known and
> well controlled. I would like to figure out inhomogenities in  
> radiation flux over the
> IR detector array due to different system setups and things like  
> that. By the way
> the basic IR detectors will reside in a vacuum and their  
> temperature will be controlled
> isolated from the rest of the system. So I think convection should  
> not play a role
> in that case.
>
> I have to thank you once again - I know this has nothing to do with  
> your expertise
> and I can imagine there is stuff you like to do more than answering  
> my ongoing mails ;).
> But if you think there is any hope in using Radiance for this issue  
> it would really help
> me if you could give me a kick on how to model those self-luminous  
> materials. I will
> have to validate the results some day, anyway.
>
> I must say that I find it very hard to figure out much more than  
> the basic scene generation
> and rendering mechanisms from the freely available documentation,  
> but I'm not to
> experienced with all this stuff, yet.
>
> Thanks,
> Alex


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