[Radiance-general] Reduce rtrace runtime

[Jia Hu]

Hello Greg:

For example, for the sky same conditions, I run twice and the results are as
follows (each means illuminance of a point). The sky luminance distribution
is generated by the gendaylit program.

MM:1-DD:2-Hour:9-Angle:0
802.381766
614.023063
395.616407
319.185386
MM:1-DD:2-Hour:9-Angle:0
907.889248 (larger than 802)
614.848339
393.397623
294.201388 (smaller than 319)

Cheers,
Jia



On Tue, Aug 31, 2010 at 11:28 AM, Greg Ward <gregoryjward at gmail.com> wrote:

> You don't say which way the differences go.  Are they consistently higher
> or lower?  If higher, then you may be getting a more accurate result from
> the path tracing method due to Russian-roulette termination.  If the path
> tracing results are lower, then you may need to decrease the -aw value
> further.
>
> To answer your earlier quesiton, the -lr setting should be greater (in
> absolute value) than the -ab setting.  They are similar.  The reason a
> separate -ab setting is provided is because indirect irradiance is much more
> expensive to compute than other types of reflection, such as specular rays
> that do not create multiple branches in the ray tree.
>
> Best,
> -Greg
>
> > From: Jia Hu <hujia06 at gmail.com>
> > Date: August 31, 2010 7:01:25 AM PDT
> >
> > Hello Greg:
> >
> > The speed is pretty fast. But I found there was a 10% difference
> sometimes even if I use the following command (ab=8 and ad = 4096). Should I
> further decrease lw to reduce the variance between each run?
> >
> > rtrace -w -h -I -ab 8 -n 4  -ad 4096 -as 0 -aa 0 -lw 1e-5 -lr -10 -u+
> office.oct < points.inp
> >
> > Thanks,
> > Jia
>
> ---------
> > From: Jia Hu <hujia06 at gmail.com>
> > Date: August 30, 2010 10:42:45 PM PDT
> >
> > Hello:
> >
> > Radiance works by calculating three parts, direct, specular and indirect.
> ab determines the number of ambient bounces (indirect part). But ab has a
> similar meaning with "lr". What is the difference between them?  Is that
> right lr (positive) should be larger than ab?
> >
> > As always, thank you,
>  > Jia
>
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