[Radiance-general] Spots when recreating Turrell installation

[Mark Stock]

Greg, interested parties,

Looking back at the hole in the wall (made with antimatter) I noticed
that even putting the "light bulb room" wall material and the
antimatter material in the ambient exclude list, there was still
ambient light pouring from the little room into the main viewing room.
That's what was causing the errant ambient spots. Possibly because
antimatter messes up the ambient exclude logic?

As soon as I changed the color of the little "light bulb room" to pure
black, the situation improved:

Old: http://markjstock.org/transfer/img06.png
New: http://markjstock.org/transfer/img11.png

Ambient parameters might actually be too high. But the rendering looks
nice! Turrell must have used a very black little room for his light
source!

Files: http://markjstock.org/transfer/afrum1.tar

Improvements/comments welcome. More Turrell pieces are in the works,
as I figure them out.

Mark

On 9/2/13, Greg Ward <gregoryjward at gmail.com> wrote:
> Hi Mark,
>
> Funny you should be trying to simulate this -- my wife (who is an artist
> herself) was just down in L.A. and Turrell has what must be a very similar
> exhibit there, as she sent me a nearly identical photo of it.
>
> My first guess would be the same as yours, which would be to crank the -ad
> parameter much higher.  You may not need to increase the -as all that much.
> Finding the bright spots is the difficult part, since it is so near the
> horizon as seen from points on the adjacent walls.  (Cosine-weighted
> sampling means that the horizon gets fewer samples than the zenith.)
>
> To avoid any contributions from the source box, make the surrounding out of
> a special material and name it with an -ae option.
>
> Failing that, I would go full Monte Carlo and see if that works:
>
> 	-aa 0 -ad 1024 -as 128 -lw .0002 -ab 2
>
> Your scene breaks one of the basic assumptions in the Radiance indirect
> calculation, which says that indirect lighting is fairly well-distributed in
> the space.  Here, you have a patch acting as a light source.
>
> Once I implement the irradiance Hessian described in the recent Siggraph
> Asia paper by Schwarzhaupt et al., the situation might improve:
>
> 	http://zurich.disneyresearch.com/~wjarosz/publications/schwarzhaupt12practical.html
>
> Best of luck!
> -Greg
>
>> From: Mark Stock <mstock at umich.edu>
>> Date: September 1, 2013 8:08:28 PM PDT
>>
>> Folks,
>>
>> If you have the chance to go to the Guggenheim in NYC, go and see the
>> James Turrell exhibit. You've never seen the Guggenheim quite like
>> this before, and as appreciators of light and its behavior, you will
>> find yourself both satisfied and intrigued by his installations.
>>
>> I've been working to recreate a few of them in Radiance, and am
>> running into some difficulties. One piece, "Afrum I (White)", should
>> look like this:
>> http://nyogalleristny.files.wordpress.com/2013/08/afrum1.jpg
>>
>> It's a point light in a small box above the entryway to the room, a
>> special 6-sided hole cut in the wall, and the light beams this
>> cube-like shape onto the corner. The light patch illuminates the room.
>>
>> Instead, what I get looks like this:
>> http://markjstock.org/transfer/img06.png
>>
>> Here are the relevant rendering parameters:
>> -ds 0.02 -lw 1e-5 -ab 5 -aa 0.03 -ar 256 -ad 1024 -as 512
>>
>> I suspect that I simply need more ambient subsamples, as a few ambient
>> points are catching the patch and some are not. But increasing -ad and
>> -as do nothing to improve quality.
>>
>> Or, WAIT, are those bright spots seeing the little hole (it's 6" wide)
>> through which the light is originally emerging? How can I prevent
>> that?
>>
>> Mark
>>
>
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