AW: Infrared scene simulation

radiance-general
1

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@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@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@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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