[Radiance-general] -ar, -ad, -as, ahh $#*@!

Tue, 09 Sep 2003 12:59:15 -0400

Hi Rob,

Just to weigh in below.....

Rob Guglielmetti wrote:

> thanks everyone!
>
> Mark, just for fun, I'm trying your -aa 0 -ad 16 trick right now 
> (it'll be a while before I can post a result, methinks).
>
> Martin, yours was a good heads up as to the essence of the problem -- 
> once again I'm expecting brute force CPU cycles to make up for a lack 
> of understanding about the guts of Radiance.
>
> This is good, though.  I finally realize that mkillum can be thought 
> of as a way of rolling your own ies files, sorta.
>
> Greg Ward wrote:
>
>> Hi Rob,
>>
>> This seems to be a classic example of where you just can't rely on 
>> the interreflection calculation in Radiance to solve your problem for 
>> you.  The basic assumption in this approximation is that the indirect 
>> illumination varies slowly over surfaces, which clearly isn't the 
>> case in this scene.
>
>
> er, right.  =8-/
>
>> Solution: you need to apply mkillum to create pseudo light sources 
>> (imposters) for your indirect luminaires.  To do so, put a shallow 
>> box with an open top around a single ceiling-mounted light source (5 
>> rectangles) and use the "void" modifer for these, making sure they 
>> face out into your room.  Let's say you called this file 
>> "light_in.rad".  Using either the octree for your room or a reduced 
>> one that just has that one light source switched on (better), you 
>> would run mkillum thus:
>
>
> lemme make sure I understand; these 5 rectangles would define the 
> inside recess of the coffer, yes?  And I would call it out like so:

Actually, what I think Greg means here is that you place an open top box 
to enclose a selected coffer in this case. For example 4 polygons that 
form the perimeter around the coffer and are "extruded" (for lack of a 
better term) down from the ceiling/coffer surface, these polygons should 
be capped with a 5th that in essence encloses the coffer. Note that the 
normals for these polygons must all point out into the the room. The 
function of this box is to "catch" the light from the true sources in 
the coffer  in the mkillum calculation and then subsequently serve as 
the light emitting surfaces (hidden because they are illums) for the 
coffer based on the data that is generated by the mkillum calc. The 
appearance of the light in the coffer itself can be controlled by using 
glow surfaces in place of the light sources in the coffer with a radius 
applied for each glow to enable the glow some minimal calculation 
ability within the coffer and behind the illum.

>
> void polygon coffer.top
> 0
> 0
> 12
>     0 0 -5
>     0 10 -5
>     10 10 -5
>     10 0 -5
>
> ... and so on?
>
> For the
>
>> sake of calculational efficiency, I recommend that you also change 
>> the light primitives in your original luminaire files to the "glow" 
>> type with an effective distance equal to the diagonal of your 
>> luminaire dimension, so as to avoid sending shadow rays to these 
>> sources unnecessarily.
>
>
> I *think* I understand...
>
>> The net result should be a fast and accurate rendering of your space.
>
>
> That's all I ever wanted. =8-)
>
> I'll try these suggestions. Thanks guys.
>
> ----
>
>      Rob Guglielmetti
>
> e. [email protected]
> w. www.rumblestrip.org
>
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>

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