[Radiance-general] Re: Illums and 3 Sided Polygons

[Marcus Jacobs]

Thanks Greg for the information. I did increase the roughness value and I 
did get what I was looking for. I tried it with a window with a trifold 
arch. Here is the result:

http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=fd57.jpg



Marcus


>Date: Mon, 6 Sep 2004 22:55:00 -0700
>From: Greg Ward <gward at lmi.net>
>Subject: Re: Illums and 3 Sided Polygons
>Hi Marcus,
>
>The trouble with your floor is that you have specified a very small,
>but non-zero value for the surface roughness.  Radiance employs a
>hybrid technique for computing specularity, which does a closed-form
>computation of specular highlights related to light sources (including
>your illum's) plus a Monte Carlo sampling of other soft-specular
>reflections.  If you set the roughness to zero, you will see a perfect
>mirror reflection of the window, without artifacts.  Presumably, this
>is not what you are after.  Alternatively, you may increase your
>surface roughness value and your reflection will improve.  Finally, you
>can set the surface roughness to zero, then apply the included
>"gloss.cal" function to achieve a pure Monte Carlo sampling of
>reflected rays.  This will lead to greater noise in the result, but
>will eliminate the source sampling artifacts you are now seeing:
>
>wood_pattern texfunc mc_roughness
>4 gloss_dx gloss_dy gloss_dz gloss.cal
>0
>3 .02 .02 .02
>
>mc_roughness plastic wood_flooring
>0
>0
>5 .5 .2 .05 .02 0
>
>Of course, I am only guessing on the parameter values, but this should
>give you an idea of what I mean.
>
>-Greg
>
> > From: "Marcus Jacobs" <marcdevon at hotmail.com>
> > Date: September 6, 2004 3:52:37 PM PDT
> >
> > Greg,
> >
> > I did read through the previous threads about the illums about one
> > month ago. Though my question was similar in nature, I was looking for
> > a more theoretical explaination of what goes on because I had been
> > encountering some issues with some illums that I had placed outside of
> > a window.
> >
> > As I mentioned before, I was getting some very strange looking
> > reflections on the floor of my renders. Here is an example:
> >
> > http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=1736.jpg
> >
> > The window has a dog ear arch. The rectangular bottom part of the
> > window I probably could have made into an illum while placing a
> > separate illum outside for the upper portion of the window. Instead I
> > used illums placed outside the entire window. While reading through
> > RWR in the section explaining the adaptive source subdivision, it
> > mentions that large light sources can be a significant source of error
> > in a standard ray-tracing calculation. Because of this, the illum
> > plane I created consisted of 8 sub-planes (similar to the illum planes
> > created in the museum scene in RWR. The only difference is mkilum
> > create the distribution instead of winbright). For some reason this is
> > what is causing a significant problem with the reflection. Why is
> > this? It seems that the rendering would be better because the illum
> > sources are smaller. Anywho, I did take your advise and I made 1 large
> > plane instead of the multiple subplanes. The reflection did improve.
> > Here is what I came up with:
> >
> > http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=d860.jpg
> >
> >
> > You can see that the reflection is improved. It still isn't completely
> > natural but it isn't as disurbing as the first picture. I set -ds to
> > 0.1 and -dj to 0.75 for this rendering. I attempted to do three things
> > in order to improve the reflection. None exactly worked. The first
> > method I tried was decreasing the -ds parameter. I used a rediculously
> > low number (0.001) with -dj set to 0.3 to see what would come out.
> > Unfortunately,there wasn't any improvement. Here is the result:
> >
> > http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=1dad.jpg
> >
> > I do not know if the lack of improvement was do any limit in Radiance
> > for the -ds parameter. The second method I used to attempt improve the
> > reflection was to increase the sampling density (i.e., increase the
> > image size). I rendered the reflection at 12 times the final image
> > size. There wasn't any improvement using this method either. Here is
> > the result:
> >
> > http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=dfa5.jpg
> >
> > Any improvement over the previous image was due to the higher direct
> > jittering setting (0.65 vs 0.3). The last method I tried was
> > increasing the direct jittering parameter to 0.85. Here is the result:
> >
> > http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=5814.jpg
> >
> > There is a noticable improvement although not completely natural.
> > There were no failures with the illums (there were created as perfect
> > squares) but all my other light sources generated "aiming failure"
> > error messages so this isn't a good solution.
> >
> > Does any know of any ways that I maight improve the reflection? Please
> > help.
> >
> > Marcus
>
>
>
>
>------------------------------
>
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>
>End of Radiance-general Digest, Vol 7, Issue 3
>**********************************************

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