Understanding illum correctly?

Greg, Carsten - thanks for your help. I really appreciate it. I just
wanted to make sure I was understanding things correctly, so forgive
these two questions:

As I understand it now, there are three ways to wind up with illum
sources in your .oct file:
1. Use the illum material type. Run 'oconv' as normal.
2. Use rad and place all of the 'illums' (using whatever secondary
material) into a separate file. This runs mkillum automatically.
3. Use mkillum manually. (This is the same as 2 above?)
As I type this out it makes perfect sense. Perhaps I have a tendency to
overthink things.

One thing I noticed is that the window_dist type is replaced with a
simple glass type. Is this because the reflectance/appearance of the
skylight doesn't matter due to it being mostly hidden? Is it correct to
assume that if I had a sidelight window in my final scene, I would
include the "skyfunc brightfunc window_dist 2 winxmit winxmit.cal 0 0"
bit to make the window appear as a real window?


Mark Shewfelt
Enermodal Engineering Ltd.
Kitchener Ontario Canada


-----Original Message-----
From: radiance-general-bounces@radiance-online.org
[mailto:radiance-general-bounces@radiance-online.org] On Behalf Of
Gregory J. Ward
Sent: December 7, 2006 6:08 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] Understanding illum correctly?

Hi Mark,

I realize this is confusing, but basically you want to put a "void"
polygon in front of your opening. Carsten is correct that the polygon
needs to point into the room, but some other slight modifications are
necessary as well to work with rad, as identified below. It is probably
better just to use a pane of glass instead of an illum initially.

From: Mark Shewfelt <MShewfelt@enermodal.com>
Date: December 7, 2006 1:25:21 PM PST

Hello All,

I hoping someone can help me with my understanding of illum sources.
I've read RwR, done the tutorials, etc., and I think I'm OK with the
concept of secondary sources. All of the examples I've seen make
illums around windows and skylights. My situation is slightly
different - I have a skylight that is not flush with the interior of
the space (i.e.
there is a well, the insides of which are painted white).

  ----------- <-- skylight glass
  > >
  > > <-- well
  > >
  > >
-- __ --------------- <-- ceiling of room
      -------------------- illum

   <- room ->

My intention is to make an illum at the ceiling of the room, which
incorporates the bounces that the light takes to get into the room.
Using the files below I've been able to simulate the skylight and the
results look pretty reasonable. However, when I run the simulation
using rad, I get the error message 'warning - no light sources found'.

From reading Axel Jacobs' excellent tutorials I was imagining that
this message would go away with the illums.

Any comments/tips/pointers would be great.


Mark Shewfelt
Enermodal Engineering Ltd.
Kitchener Ontario Canada

scene = sky.rad
scene = material.mat
scene = room3.rad
illum = skylight.rad
# The file in which to store indirect values AMB= simple.amb INDIRECT
= 2 mkillum= -ab 2

skyfunc brightfunc window_dist
2 winxmit winxmit.cal

window_dist glass skylight_glass
3 0.8 0.8 0.8

Replace the above with simple, clear glass type:

void glass skylight_glass
3 0.96 0.96 0.96

# light is emitted from this but is invisible.
void illum skylight_illum
3 0 0 0

You can take the illum out, as we won't need it (and the zeroes
shouldn't be there, as Carsten mentioned).

# light enters skylight well from here skylight_glass polygon
skylight_window 0 0
   5.491076 6.503552 3.400000

   4.201076 6.503552 3.400000

   4.201076 5.213552 3.400000

   5.491076 5.213552 3.400000

Take the above and put it into room3.rad, as you won't be making it into
an illum with mkillum. The "illum=" line in your rad input file is for
surfaces to be made into illum's, only. Orientation doesn't matter in
this case.

# light is emitted from this "surface" into the room skylight_illum
polygon face.65 0 0
   5.491076 6.503552 3.00000

   4.201076 6.503552 3.00000

   4.201076 5.213552 3.00000

   5.491076 5.213552 3.00000

As Carsten points out, you need to reverse your vertex order:

# light is emitted from this "surface" into the room void polygon
face.65 0 0
   5.491076 5.213552 3.00000
   4.201076 5.213552 3.00000
   4.201076 6.503552 3.00000
   5.491076 6.503552 3.00000

Notice that I replaced the modifier with "void." Mkillum will take this
file and compute an appropriate output distribution based on the light
entering the space and up to 2 indirect bounces. (This may be modified
by setting the "mkillum=" variable in rad.)


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