[Radiance-general] Multiple spherical glow sources?

[Mark Stock]

The star map that I have now is LDR, but I intend to create a new 
HDR version using the raw star data from Tycho-2. Unfortunately, 
there are stars everywhere, so I'd need illums to cover pretty 
much the whole hemisphere. Since that'll wind up being 50-200 of 
them, it will cost a lot in render-time, and add some complexity 
to the preprocessing. This is disappointing because a single glow 
source would have sufficed, and accomplished almost the same 
thing.

Do "illum" surfaces respond to "rpict -ds" ? I'll want smooth 
penumbras. If so, I can get by with fewer illums.

Mark

On Mon, 14 Sep 2009, Jack de Valpine wrote:

> Hi Mark,
>
> Is your high-res image an hdr? If so would it be worth looking into mksource 
> to recover broad areas of the sky (clusters of star) as illum sources? Then 
> your high res image can be mapped onto a glow source with the lighting 
> provided by a set of illum sources (multiple ones with varying solid angles), 
> derived from the hdr.
>
> -Jack de Valpine
>
>
> Mark Stock wrote:
>> Hello,
>> 
>> I am working on a star map for use with night renderings, and it seems like 
>> it should be decomposed into two layers: one is a high-resolution imagemap 
>> showing the stars themselves, the other is a low-resolution "light map" 
>> that should be used to actually illuminate the scene.
>> 
>> The problem is that I want the "light map" layer to do the illumination, 
>> but I don't want it to be visible. I want the image map to appear in the 
>> sky in the final rendering.
>> 
>> I know that I can use maxrad=-1 in the image map glow source to prevent it 
>> from contributing to scene illumination, and maxrad=0 to allow the light 
>> map to illuminate. But mixfunc must be placed between the colorpict and the 
>> glow source, forcing me to either allow both to illuminate, or neither. But 
>> when the imagemap contributes to illumination, the result is very noisy 
>> (obviously).
>> 
>> This wouldn't be a problem if I could use two sky-dome sized glow sources 
>> in the same scene: "skyglow source skydome 0 0 4 0 0 1 360". But Radiance 
>> only sees the last one to be defined.
>> 
>> And I can't make the light map into an "illum" because it then gets treated 
>> as a point source at the zenith of my "source" description (ignoring the 
>> 180-degree size of the source disc).
>> 
>> Do I need to add transparency to the imagemap before making it into a 
>> rad=-1 glow source, so that when a ray is traced between the stars, it hits 
>> the illuminating light map rad=0 glow source? I am reluctant to include 
>> another circa-gigabyte imagemap to the scene just for that.
>> 
>> Am I missing something else or is this impossible?
>> 
>> Mark
>> 
>> PS. Shouldn't the file size limit for colorpict images be raised? I get a 
>> warning for using even a 134MB picture file. I intend to go much larger.
>> 
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>
>
> -- 
> # Jack de Valpine
> # president
> #
> # visarc incorporated
> # http://www.visarc.com
> #
> # channeling technology for superior design and construction
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