Understanding rvu options

Dear radiance-general,

I'm trying to fully understand all the options provided by rvu. This was brought
up in a simple scene test I am trying out.

The scene definition is as such, with a sunny sky: https://pastebin.com/VWcmgmR4
Which produces this image: https://ibin.co/3q18YxSiOc2C.png

But when I change gensky to a cloudy sky: https://pastebin.com/swR7MFhu
I get this: https://ibin.co/3q18v7qVrDXc.png

In order to get the leaves actually rendering and to get the shadows of the
leaves less splotchy, I've had to increase -ps to 1 and -ar to 2048. My full
options are -ab 2 -ad 4096 -ar 2048 -ps 1. Is this the right approach?

I feel guilty that I am adjusting these parameters to get a more "believable"
image without fully understanding it -- I might compromise the validity of the
simulation (although yes, the material in this test is nonsense, of course).

Where can I read to learn more about the mechanics of Radiance and its options
(in more detail than the man pages, and preferrably not hard math, as that is
not my strength) so that I can better understand the knobs I am turning?

Kind regards,

···

--
Dion Moult

What you're seeing makes sense to me, that the quality of rendering relies more on ambient calculation parameters when the calculation is 100% diffuse/ambient light, without a direct light source.

You also seem to be moving the parameters in the direction of higher accuracy and longer rendering time so shouldn't be detracting from validity.

As for reading materials, I'm sure lots of people could make suggestions. The book Rendering with Radiance is likely a top suggestion. Also, here's a presentation that I recently re-discovered from a past annual workshop:

Actually you could browse all the past workshop presentations for relevant materials, although I'm not sure how easy it will be to judge them by the titles.
https://www.radiance-online.org/community/workshops

Regards,
Chris

···

-----Original Message-----
From: Dion Moult [mailto:[email protected]]

In order to get the leaves actually rendering and to get the shadows of the leaves less splotchy, I've had to increase -ps to 1 and -ar to 2048. My full options are -ab 2 -ad 4096 -ar 2048 -ps 1. Is this the right approach?

I feel guilty that I am adjusting these parameters to get a more "believable"
image without fully understanding it -- I might compromise the validity of the simulation (although yes, the material in this test is nonsense, of course).
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The default parameters are set in rvu for speed over accuracy. Decreasing the value of -aa will help a lot with your scene.

I recommend learning to use rad and/or trad to help set rendering parameters based on easier-to-understand variables. Here is a paper on the subject:

  http://radsite.lbl.gov/radiance/papers/erw95.1/paper.pdf

And of course the man page is always a reasonable place to start:

  https://www.radiance-online.org/learning/documentation/manual-pages/pdfs/rad.pdf

Cheers,
-Greg

···

From: Christopher Rush <[email protected]>
Date: January 30, 2018 1:04:22 PM PST

What you're seeing makes sense to me, that the quality of rendering relies more on ambient calculation parameters when the calculation is 100% diffuse/ambient light, without a direct light source.

You also seem to be moving the parameters in the direction of higher accuracy and longer rendering time so shouldn't be detracting from validity.

As for reading materials, I'm sure lots of people could make suggestions. The book Rendering with Radiance is likely a top suggestion. Also, here's a presentation that I recently re-discovered from a past annual workshop:
https://www.radiance-online.org/community/workshops/2011-berkeley-ca/presentations/day1/JM_AmbientCalculation.pdf

Actually you could browse all the past workshop presentations for relevant materials, although I'm not sure how easy it will be to judge them by the titles.
https://www.radiance-online.org/community/workshops

Regards,
Chris

-----Original Message-----
From: Dion Moult [mailto:[email protected]]

In order to get the leaves actually rendering and to get the shadows of the leaves less splotchy, I've had to increase -ps to 1 and -ar to 2048. My full options are -ab 2 -ad 4096 -ar 2048 -ps 1. Is this the right approach?

I feel guilty that I am adjusting these parameters to get a more "believable"
image without fully understanding it -- I might compromise the validity of the simulation (although yes, the material in this test is nonsense, of course).