ambient accuracy parameter

Hi,

I've been reading some previous posts related to ambient parameters settings and I have some questions.

When it is recommendable to use -aa 0 value? If I understand this parameter well, 0 value turns off irradiance caching, so we can use it when caching isn't needed (mkillum calculation for venetian blinds or rtcontrib).
When we set -aa 0, does -ar have influence on minimum sampling distance, since: min sampling distance = max scene dimension* aa/ar.

When I run a rtrace calculation with -aa 0, calculation time is much shorter than with -aa 0.1. Why?

Have a nice holidays :slight_smile:
Marija.

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I use the -aa setting to get a smoother indirect calculation. This is especially important if the -ad parameter is low, i.e., <=512. A high -aa parameter, such as 5000 or whatever, creates a dense grid of indirect/reflected values. You can check that by making two images, one with a low setting of ad and aa, and one with a low setting of ad and a high setting of aa. That will show you immediately what the ambient accuracy parameter is about. The image contains less blotches.

Martin Moeck

···

-----Original Message-----
From: radiance-general-bounces@radiance-online.org on behalf of Marija Cvetkovic
Sent: Tue 12/26/2006 2:30 AM
To: Radiance general
Subject: [Radiance-general] ambient accuracy parameter

Hi,

I've been reading some previous posts related to ambient parameters
settings and I have some questions.

When it is recommendable to use -aa 0 value? If I understand this
parameter well, 0 value turns off irradiance caching, so we can use it
when caching isn't needed (mkillum calculation for venetian blinds or
rtcontrib).
When we set -aa 0, does -ar have influence on minimum sampling distance,
since: min sampling distance = max scene dimension* aa/ar.

When I run a rtrace calculation with -aa 0, calculation time is much
shorter than with -aa 0.1. Why?

Have a nice holidays :slight_smile:
Marija.

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Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi Martin,

You are talking about ambient resolution (-ar) parameter. For -aa images are better with lower settings of -aa, and maximum recommended value is 0.3.
I know what this parameter means for rendering, but my question is when value -aa 0 should be used and when not?

Marija

Martin Moeck wrote:

···

I use the -aa setting to get a smoother indirect calculation. This is especially important if the -ad parameter is low, i.e., <=512. A high -aa parameter, such as 5000 or whatever, creates a dense grid of indirect/reflected values. You can check that by making two images, one with a low setting of ad and aa, and one with a low setting of ad and a high setting of aa. That will show you immediately what the ambient accuracy parameter is about. The image contains less blotches.

Martin Moeck

-----Original Message-----
From: radiance-general-bounces@radiance-online.org on behalf of Marija Cvetkovic
Sent: Tue 12/26/2006 2:30 AM
To: Radiance general
Subject: [Radiance-general] ambient accuracy parameter
Hi,

I've been reading some previous posts related to ambient parameters settings and I have some questions.

When it is recommendable to use -aa 0 value? If I understand this parameter well, 0 value turns off irradiance caching, so we can use it when caching isn't needed (mkillum calculation for venetian blinds or rtcontrib).
When we set -aa 0, does -ar have influence on minimum sampling distance, since: min sampling distance = max scene dimension* aa/ar.

When I run a rtrace calculation with -aa 0, calculation time is much shorter than with -aa 0.1. Why?

Marija,

I use -aa 0 for models which contain massive amounts of detail and for which computing and storing enough ambient points would quickly run me out of memory. The first scene to require this was

http://mark.technolope.org/image/p36.html

but I have used it on most of my work since then.

I did a little work with -aa 0 before this and found that oversampling combined with low -ad could produce good images. I made a page showing the results:

http://mark.technolope.org/radmisc/aa0_ps1_test/final.html

I hope this helps you.

Mark
mstock@umich.edu

···

On Wed, 27 Dec 2006, Marija Cvetkovic wrote:

Hi Martin,

You are talking about ambient resolution (-ar) parameter. For -aa images are better with lower settings of -aa, and maximum recommended value is 0.3.
I know what this parameter means for rendering, but my question is when value -aa 0 should be used and when not?

Marija

Martin Moeck wrote:

I use the -aa setting to get a smoother indirect calculation. This is especially important if the -ad parameter is low, i.e., <=512. A high -aa parameter, such as 5000 or whatever, creates a dense grid of indirect/reflected values. You can check that by making two images, one with a low setting of ad and aa, and one with a low setting of ad and a high setting of aa. That will show you immediately what the ambient accuracy parameter is about. The image contains less blotches. Martin Moeck

-----Original Message-----
From: radiance-general-bounces@radiance-online.org on behalf of Marija Cvetkovic
Sent: Tue 12/26/2006 2:30 AM
To: Radiance general
Subject: [Radiance-general] ambient accuracy parameter
Hi,

I've been reading some previous posts related to ambient parameters settings and I have some questions.

When it is recommendable to use -aa 0 value? If I understand this parameter well, 0 value turns off irradiance caching, so we can use it when caching isn't needed (mkillum calculation for venetian blinds or rtcontrib).
When we set -aa 0, does -ar have influence on minimum sampling distance, since: min sampling distance = max scene dimension* aa/ar.

When I run a rtrace calculation with -aa 0, calculation time is much shorter than with -aa 0.1. Why?

_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi Mark,

Thanks for the links.
The results for -aa 0, low -ad and oversampling can be really useful.

BTW your site is really great :slight_smile:

Marija.

Mark Stock wrote:

···

Marija,

I use -aa 0 for models which contain massive amounts of detail and for which computing and storing enough ambient points would quickly run me out of memory. The first scene to require this was

http://mark.technolope.org/image/p36.html

but I have used it on most of my work since then.

I did a little work with -aa 0 before this and found that oversampling combined with low -ad could produce good images. I made a page showing the results:

http://mark.technolope.org/radmisc/aa0_ps1_test/final.html

I hope this helps you.

Mark
mstock@umich.edu

Mark,

Awesome pictures. What are the limitations of your low -ad and high over sampling approach? When is appropriate and when is it not appropriate?

Probably not something you are concerned about in your work, but when you use such a low -ad setting and such a high over sampling rate, I'd like to know what effect there is on overall light level accuracy in a typical interior space with daylighting and/or electric lighting?

I guess there is no over sampling on an rtrace calculation, but for an irradiance calculation image, my -ad setting is usually in the thousands and my ambient bounces are at 4 or so (depending on the results of a parameter test) I'm guessing the -ab and -ad parameters can't be reduced if light level accuracy is important. Maybe I'm wrong? Sure would be nice to slash some of those crazy calculation times.

Mark

Mark,

Awesome pictures. What are the limitations of your low -ad and high over sampling approach? When is appropriate and when is it not appropriate?

Mark,

One disadvantage is hard drive space: how many 3 GB images can I keep around? Another problem that occurs more with some pieces then others is speckles caused by particularly bright pixels. Since pfilt works on the full dynamic range, a single super-bright pixel in the full-res image can cause a significant bright spot in the final reduced-res image. Note the speckles in this image:

http://mark.technolope.org/image/p54.html
http://mark.technolope.org/image/img54_detail_900.png

That second image is at print resolution, and was filtered down from a 4x or 6x resolution original. That scene is very contrasty. Some of my more recent work mitigates the speckling by rendering in a closed room: allowing enough bounces to provide a more even background.

I find that "-aa 0" is appropriate when the octree for a scene with little overlapping geometry takes more than a few hundred MB to create. Or for scenes in which I want detailed interreflection among a great number of very tiny surfaces (probably the same thing). It seems to me to be an easy way to get rid of the splotches that plagued some of my earlier renderings.

Probably not something you are concerned about in your work, but when you use such a low -ad setting and such a high over sampling rate, I'd like to know what effect there is on overall light level accuracy in a typical interior space with daylighting and/or electric lighting?

I have not studied this at all. I could posit that the low -ad with high oversampling rate allows me to bias the interreflection toward the first (and most important) bounce. Shooting 36 rays into a final image pixel (what 6x oversampling does) but letting each of those only spawn 8 child rays (-ad 8) at the second and deeper levels effectively means that I'm doing a more accurate 1st bounce.

I guess there is no over sampling on an rtrace calculation, but for an irradiance calculation image, my -ad setting is usually in the thousands and my ambient bounces are at 4 or so (depending on the results of a parameter test) I'm guessing the -ab and -ad parameters can't be reduced if light level accuracy is important. Maybe I'm wrong? Sure would be nice to slash some of those crazy calculation times.

My impetus was to slash the computation times and fit the problem in memory. Of course, back then I had 2 GB of RAM *at most* and no access to anything better than a dual-proc machine. Now I am blessed with access to a 32 GB monster 8-core intel box and a number of medium-sized clusters.

One other advantage of "-aa 0" is that one pixel trace does not depend on another, so parallelization is trivial. I use rpiece almost exclusively for my big jobs now. OpenMP or pthreads anyone?

Mark

···

On Thu, 28 Dec 2006, Mark de la Fuente wrote:

Just wanted to chime in on this thread. The -aa 0 setting is appropriate when you have a lot of small geometry that isn't safe to leave out of the ambient calculation (using the -ae or -aE options), or for special applications such as mkillum or rtcontrib. Turning off the ambient cache is NOT a good idea when what you care about is individual ray accuracy, such as when you are using rtrace to evaluate radiance or irradiance values in a space. It can be done with -aa 0, but you have to pay close attention to your other parameter settings (such as -ad, -as, -lw, and -lr) and alter them appropriately. The -ar setting has no effect with -aa 0. Ditto for -aw.

-Greg

···

From: Marija Cvetkovic <cveleglg@bankerinter.net>
Date: December 26, 2006 1:30:46 AM PST

Hi,

I've been reading some previous posts related to ambient parameters settings and I have some questions.

When it is recommendable to use -aa 0 value? If I understand this parameter well, 0 value turns off irradiance caching, so we can use it when caching isn't needed (mkillum calculation for venetian blinds or rtcontrib).
When we set -aa 0, does -ar have influence on minimum sampling distance, since: min sampling distance = max scene dimension* aa/ar.

When I run a rtrace calculation with -aa 0, calculation time is much shorter than with -aa 0.1. Why?

Have a nice holidays :slight_smile:
Marija.

1 Like

For internet searchers finding this page, the links above have been moved. You can find the ambient study at Radiance ambient and penumbra test v2.0 and the “p36” artwork at the bottom of Artwork: Streamlines marked “Turbulence Infinite”.

1 Like