[Radiance-general] ar and aa

[Reinhart, Christoph]

I share Jia's confusion. Greg, I remember that we had asked you the same
question during the Radiance workshop last year but I still do not get
it? Could you explain the relationship between aa and ar one more time?

 

Christoph

 

From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Jia
Hu
Sent: Monday, July 19, 2010 1:48 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] ar and aa

 

Sorry for the typo, I meant to compare "-ar" and "-aa".   I can
understand your explanation as to -ar and -aa.

 

The book and some online materials also discussed about the meaning of
-ar and -aa. And they seem to explain it from a different perspective.
For my understanding of those statements, the interpolation will always
happen when the distance between two points is less than minimum spacing
distance (sceneSize * aa /ar). When the distance between two points is
larger than the minmum spacing distance, interpolation may happen if the
point is within the "radius of validity" of another point. In other
words, the minimum "radius of validity" is sceneSize *aa /ar? 

 

According to Greg's explanation, when the point falls within SceneSize /
ar, the accuracy starts to relax. Can I say that when the error gets its
maximum, -aa, when the point falls within the minimum spacing distance
(SceneSize *aa /ar)?   I know there must be something wrong with my
understanding about this issue. But I can not find where the problem is.


The book Rendering with Radiance says "  -ar parameter acts as a
limiting device and If you are already running up against the -ar limit,
increasing the setting will result in a higher density of sampling. If
the limit has not been reached, then increasing -ar should have no
effect." I also have difficulty in understanding the term "limiting
device".

 

Thank you for help.

 

Jia Hu

On Mon, Jul 19, 2010 at 2:31 AM, Greg Ward <gregoryjward at gmail.com>
wrote:

I assume you meant to compare "-aa" and "-ar" in your first sentence.
These are not two variables that affect the same behavior -- not much
point in that.  Rather, think of the -ar setting as determining a scene
resolution below which the accuracy of the indirect calculation (as
determined by the -aa parameter) will start to relax.  If you divide
your global scene size (the fourth value reported by "getinfo -d
octree") by the -ar setting, you will get the scene size below which the
indirect calculation will begin to lose accuracy.

Best,
-Greg

From: Jia Hu <hujia06 at gmail.com>
Date: July 16, 2010 8:17:48 PM PDT 



Hello experts:

Is that right doubling the value of "aa" has the same effect as
decreasing the value of "aa" by half?  The minimum distance between
sampling points is the same according to the formula: SceneSize * aa /
ar.

Cheer,
Jia

 

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