[Radiance-general] ar and aa

[Jia Hu]

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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