[Radiance-general] Re: physically-based landscapes

[Carsten Bauer]

Hi all,

some more thoughts from my side ... I have the assumption that this is one of 
those problems where one can easily miss something in the argumentation.

1) where to put the HDR image:

At the moment I'm a bit puzzled, too. If one maps an HDR image representing a 
view of an outside landsacpe onto a window pane, - isn't this only exact for 
this special point of view? Other rays from somewhere else in the room 
hitting the illum made out of the image , won't they get assigned a wrong 
value? (Just read Peter's mail, which in fact gives an answer to this...)

At least this is the thinking behind the idea of mapping the landscape view to 
- example -  a 100 m radius sphere like a dome over a 10x10x10m scene, thus 
making parallax errors reasonably small, by keeping the blowing up of the 
scene reasonable, too.. (Perhaps not as small as I think, I have to look at 
Peter's examples..) The drawback of this method is, that such a large source 
cannot be treated with the direct calc. anymore (illum/light) but must be 
used as glow with 4. param zero and thus considered wtihin the ambient 
calculation, affording in turn sufficiently high ambient parameters for a 
trustworthy rendering. If you use the source type for the dome like Santiago 
pointed out, you can add a separate sun like it is done with the usual gensky 
procedure. 
(Never did this so far, I have to admit ...)

2) -ae / -ar

As far as I know, -ae and -ar are independent parameters. Ambient cache 
resolution specification with -ar always is relative to the whole scene 
bounding cube, no matter what sort of objects are actually present. But there 
might be another way out: imagine a small indoor scene with an adequare -ar 
setting resulting in values spaced, say, half a meter apart. If you add a 
several km wide outdoor bounding cube to it, you have to raise -ar 
respectively. Normally this would result in an exploding memory requirement 
for the ambient cache, but if everything in the outdoor part of the scene is 
excluded with -ae, only values in the indoor part will be calculated. By this 
you can have the same high absolute resolution within the indoor part like 
before, and the high -ar setting shouldn't effect calculation time/memory 
requremant at all.
(Never tried this, either, but it sounds as if it could work...)

-Carsten