[Radiance-general] Ambient mess

[Alex Summerfield]

Gidday Bruce,

Ok this is bit of a punt - and hopefully it won't end up looking like a  
dog's breakfast.

if you don't mind flat shading of the surrounding surfaces and loosing  
the light spill you could treat them as glow surfaces (with low RGBs to  
produce something equivalent to the slightly darker areas of the land  
or sea) and set the 4th parameter maxrad -ve so they don't contribute  
to scene illumination.

Effectively it should be a way of killing off the ambient calculation  
in those areas while still producing at least the presence of a  
coloured surface. Vertical surfaces might need their own lower glow  
definition to make a contrast.

The abstractness might help indicate the 'extent' of the lighting  
rendering, but if the flatness of the shading ends up being an  
aesthetic problem, then a Brightfunc could be written to modify the  
glows and slowly fade them out with distance from the project.

hope this helps
cheers
alex

*******************************************************
A. J. Summerfield                 alex@arch.usyd.edu.au
Faculty of Architecture, University of Sydney

Outside of a dog, a book is man's best friend.
Inside a dog, it's too dark to read.       Groucho Marx
*******************************************************

On 12 Nov 2003, at 2:53 pm, Bruce Sounes wrote:

> What I thought would be a straightforward night-time scene has turned  
> out not to be. The first two images at the link below shows a  
> conventional scene with the lights replmarks-ed in. All the lights are  
> based the same fitting, a Thorn Contrast C (33000lm).
>
> http://uk.f1.pg.photos.yahoo.com/ph/bsounes/lst?.dir=/ 
> ambient_mess&.view=t
>
>
>
> After doing a few test renders with just one light, a wall and a  
> ground plane I realized the splotchy areas beyond the site where the  
> result of the ambient calculation picking up the bright wall areas  
> just below the fittings. No extra ab�s, ad�s ,as�s, extra ar or  
> setting aa to 0 solved the problem. The lamp is modeled as a 10mm  
> sphere therefore source sub-structuring didn�t seem tobe the issue  
> either.
>
> This suggested to me using mkillum to eliminate the gamble of the  
> first ambient bounce finding the bright surfaces: feed the brightest  
> surfaces to mkillum while retaining the original surface modifiers for  
> the final render. This involved switching to AutoCAD to �radout� the  
> polygons (previously I was using .obj files), a degree of re-modelling  
> , checking the surface normals and splitting the model in two. The  
> result (third image: �AlternativeA_pcond�) is still less than  
> satisfactory.
>
> I experimented putting a void illum polygon a few millimeters in front  
> of the wall. A single bright splotch still appeared. There also seemed  
> to be a slightly different light distribution, which made me question  
> using opaque surfaces as illum sources.
>
> An illum �fence� could be spaced a distance from each building to try  
> and catch the splotches before they appear, but I haven�t tried that  
> yet.
>
> I am interested primarily in the final appearance of the image. The  
> illuminance beyond the site boundary is quite low - below 3 lux.
>
> Does anyone have any suggestions?
>
> Bruce Sounes
>
>