Radiance, analysis

Thanks Jack, Rob

That cleared that up for me. I understood xform array from Axel Jacobs tutorial and Thomas' example. Replmarks and ltview will prove invaluable in 'trying' out different lighting scenarios. So far I succeed I getting rvu to render and show my fixtures in sufficiently correct form, scale and presentable. Now the fun part: analysis

I used the same oct file from rvu to generate illuminance and luminance pic files. Now with ximage, the -illuminance pic I see the fixtures in black (which perhaps males sense since no light arrives at the lens right?) I did test for a room with window openings in daytime and night time:

The night illuminance pic shows the fixture lens lit and gives what seems the correct fc reading (which I must validate)
The day time illuminance pic shows the lens in black in the obviously much brighter pic (I adjusted exposure) but the ximage 'l' readings are too high for fc units but seem correct if they are lux. The key word is 'seem'.

My variables are too numerous to list here( rpict options, ximage etc.) I need to know if an irradiance pic rendered with thr -i option in rpict can be analyzed ximage so has to give lux or footcandle readings. There is sun patch in the daytime rendered scene. would that serverly impair the accuracy of pixel readings???

regards
Steve

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Date: Sun, 27 Jan 2008 19:31:21 -0500
From: [email protected]
To: [email protected]
Subject: Re: [Radiance-general] Radiance, objline, objpict etc..

Hi,

I wanted to add a few comments on this.

The "-i

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steve michel wrote:

The day time illuminance pic shows the lens in black in the obviously much brighter pic (I adjusted exposure) but the ximage 'l' readings are too high for fc units but seem correct if they are lux. The key word is 'seem'.

My variables are too numerous to list here( rpict options, ximage etc.) I need to know if an irradiance pic rendered with thr -i option in rpict can be analyzed ximage so has to give lux or footcandle readings. There is sun patch in the daytime rendered scene. would that serverly impair the accuracy of pixel readings???
  

Hi Steve,

By default, your luminance pics are in cd/m^2, and your illuminance pics are in lux. The accuracy of the rendering would not necessarily affect the accuracy of the scene; if anything, sun patches would improve the accuracy of the results for a given set of settings. I wouldn't worry about the appearance of an illuminance image, if the values are correct. I recommend you use the falsecolor tool to generate some falsecolor images of your scene, so you can do a thorough investigation of the whole image's values. And of course for absolute accuracy of a validation you should use rtrace and calculate values at specific points that you can verify with hand calcs. This will be more accurate than interpolating a glob of colors in a falsecolor image, or even picking points off the image in ximage.

Also, have you tried rad yet? rad can make very intelligent guesses about appropriate settings for rpict, based on your simple inputs of scene size (max dimension), image QUALITY (high-medium-low), VARIABILITY or range of light in the space (high-medium-low), and DETAIL or model complexity (high-medium-low). This is a great tool and you can even use it and just output the settings to a text file to inspect. You can learn about the variables that way, by changing one of the parameters above and see the ramifications on the rpict/rtrace settings. The use of rad is covered well in RwR, as is the practice of performing sensitivity studies on your models and parameters, to find a sweet spot in terms of accuracy/time. This dance is done on every project, but eventually you will develop a feel for setting these parameters, at least roughly.

- Rob Guglielmetti
www.rumblestrip.org