illuminance measurement

Hi,

I'm trying to confirm illuminance calculations but getting conflicting results. A falsecolor image generated from an irradiance image (-i option to rpict: rif file has line 'render= -i') gives an illuminance of around 400 lux in the middle of the room. Using rtrace I get an illuminance of about 210 lux in the middle of the room. (I'm using an irradiance image for the -i option in falsecolor and a radiance image for the -p option).

The rtrace I'm using is as per Axel Jacobs tutorial: echo "61.292 27.490 0 0 0 1' | rtrace -I -h -ov octrees/south.oct | rcalc -e '$1=179*$1' This should work with the octree- same as what I generated the image from- should it not?

John.

JOHN FORD

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FORTY THREE STAWELL STREET
NORTH MELBOURNE 3051
PHONE 03 9329 0709
FAX 03 9329 1780

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Hi John,

I suppose this belongs in a FAQ. If you read the fine print on the -i option, you'll see that it differs in an important way from -I. In the -i case, rays are traced to surfaces, where irradiance is then computed. Using -I, rtrace computes irradiance from input interpreted as measurement points and orientations. Thus, you don't need to have actual surfaces where you measure using -I.

In short, your two calculations are measuring different values, probably at different positions in the scene as well as in different directions.

Best,
-Greg

ยทยทยท

From: John Ford <[email protected]>
Date: August 16, 2010 3:34:22 AM GMT+01:00

Hi,

I'm trying to confirm illuminance calculations but getting conflicting results. A falsecolor image generated from an irradiance image (-i option to rpict: rif file has line 'render= -i') gives an illuminance of around 400 lux in the middle of the room. Using rtrace I get an illuminance of about 210 lux in the middle of the room. (I'm using an irradiance image for the -i option in falsecolor and a radiance image for the -p option).

The rtrace I'm using is as per Axel Jacobs tutorial: echo "61.292 27.490 0 0 0 1' | rtrace -I -h -ov octrees/south.oct | rcalc -e '$1=179*$1' This should work with the octree- same as what I generated the image from- should it not?

John.

JOHN FORD

BLUEBOTTLE
FORTY THREE STAWELL STREET
NORTH MELBOURNE 3051
PHONE 03 9329 0709
FAX 03 9329 1780

WWW.BB3.NET.AU
[email protected]
MOBILE 0411 519 738