# Luminance predictions in a plane

Dear all,

I have a question regarding the luminance prediction (cd/m2) on the plane for certain points. and any help would really be appreciated.

I have measured certain points with an luminance meter. I have used also image-based for the same points to extract the luminance and I have very similar results. I need to use also simulation-based luminance values for the same points and compare the results with the measured and image based ones.

Before, I have simulated only Illuminances. How can I measure the Luminances?

Here is the code I use to predict the illuminance:

# commands to run
commands = ["rm -f /tmp/bpi.amb",

"echo '4.52 0.85 0.74 0 0 1 " +
"3.74 1.13 0.74 0 0 1 " +
"4.52 1.13 0.74 0 0 1 " +
"5.30 1.13 0.74 0 0 1 " +
"3.74 2.13 0.74 0 0 1 " +
"4.52 2.13 0.74 0 0 1 " +
"5.30 2.13 0.74 0 0 1 " +
"3.74 3.13 0.74 0 0 1 " +
"4.52 3.13 0.74 0 0 1 " +
"5.30 3.13 0.74 0 0 1 " +

"' | rtrace -w -af /tmp/bpi.amb -as 512 -ar 64 -aa 0.15 -ab 2 -I+ -h lab.oct | rcalc -e '\$1=(\$1*0.265+\$2*0.670+\$3*0.065)* 179'",

]

Any help would be really appreciated,

Thank you very much

Best regards,

Sokol Dervishi

Dear all,

I have a question regarding the luminance prediction (cd/m2) on the plane for certain points. and any help would really be appreciated.

I have measured certain points with an luminance meter. I have used also image-based for the same points to extract the luminance and I have very similar results. I need to use also simulation-based luminance values for the same points and compare the results with the measured and image based ones.

Before, I have simulated only Illuminances. How can I measure the Luminances?

Here is the code I use to predict the illuminance:

# commands to run
commands = ["rm -f /tmp/bpi.amb",

"echo '4.52 0.85 0.74 0 0 1 " +
"3.74 1.13 0.74 0 0 1 " +
"4.52 1.13 0.74 0 0 1 " +
"5.30 1.13 0.74 0 0 1 " +
"3.74 2.13 0.74 0 0 1 " +
"4.52 2.13 0.74 0 0 1 " +
"5.30 2.13 0.74 0 0 1 " +
"3.74 3.13 0.74 0 0 1 " +
"4.52 3.13 0.74 0 0 1 " +
"5.30 3.13 0.74 0 0 1 " +

"' | rtrace -w -af /tmp/bpi.amb -as 512 -ar 64 -aa 0.15 -ab 2 -I+ -h lab.oct | rcalc -e '\$1=(\$1*0.265+\$2*0.670+\$3*0.065)* 179'",

]

Any help would be really appreciated,

Thank you very much

Best regards,

Sokol Dervishi

Hi,

To calculate Luminance instead of Illuminance just remove "-I+" flag

rtrace -w -af /tmp/bpi.amb -as 512 -ar 64 -aa 0.15 -ab 2 -h lab.oct |
rcalc -e '\$1=(\$1*0.265+\$2*0.670+\$3*0.065)* 179'

I also propose you to set higher ambient parameters ( for example -as
1024 -ar 200 -aa 0.1 -ab 5), since you only have calculation in few
points.

Hope this helps,
Marija.

···

2008/5/19 sokol dervishi <dervishi_sokol@yahoo.com>:

Dear all,

I have a question regarding the luminance prediction (cd/m2) on the plane
for certain points. and any help would really be appreciated.

I have measured certain points with an luminance meter. I have used also
image-based for the same points to extract the luminance and I have very
similar results. I need to use also simulation-based luminance values for
the same points and compare the results with the measured and image based
ones.

Before, I have simulated only Illuminances. How can I measure the
Luminances?

Here is the code I use to predict the illuminance:

# commands to run
commands = ["rm -f /tmp/bpi.amb",

"echo '4.52 0.85 0.74 0 0 1 " +
"3.74 1.13 0.74 0 0 1 " +
"4.52 1.13 0.74 0 0 1 " +
"5.30 1.13 0.74 0 0 1 " +
"3.74 2.13 0.74 0 0 1 " +
"4.52 2.13 0.74 0 0 1 " +
"5.30 2.13 0.74 0 0 1 " +
"3.74 3.13 0.74 0 0 1 " +
"4.52 3.13 0.74 0 0 1 " +
"5.30 3.13 0.74 0 0 1 " +

"' | rtrace -w -af /tmp/bpi.amb -as 512 -ar 64 -aa 0.15 -ab 2
-I+ -h lab.oct | rcalc -e '\$1=(\$1*0.265+\$2*0.670+\$3*0.065)* 179'",

]

Any help would be really appreciated,

Thank you very much

Best regards,

Sokol Dervishi

This seems to be a repeat posting of something sent out on Saturday. There is no need to post things twice -- we did get it the first time. If you are unsure if a posting has made it to the list, you can always go online to check:

I did not reply to this right away, since it is really a basic question, and I figured any number of people could handle it. In any case, a careful reading of the rtrace man page should give the answer. Quoting from the first paragraph of:

"Input for each ray is:

xorg yorg zorg xdir ydir zdir
"

You simply start the ray an arbitrary distance from your surface and give it a vector corresponding to the desired luminance measurement. The returned values (when you run rtrace without the -I+ option) will be in SI radiance units (watts/sr/meter^2),which may be converted to luminance (in candelas/meter^2) using the formula specified under the "Examples" section:

rtrace -h scene.oct <lum_meas.pts | rcalc -e '\$1=47.4*\$1+120*\$2+11.6*\$3'

I hope this helps.
-Greg

···

From: sokol dervishi <dervishi_sokol@yahoo.com>
Date: May 19, 2008 7:31:27 AM PDT

Dear all,

I have a question regarding the luminance prediction (cd/m2) on the plane for certain points. and any help would really be appreciated.

I have measured certain points with an luminance meter. I have used also image-based for the same points to extract the luminance and I have very similar results. I need to use also simulation-based luminance values for the same points and compare the results with the measured and image based ones.

Before, I have simulated only Illuminances. How can I measure the Luminances?

Here is the code I use to predict the illuminance:

# commands to run
commands = ["rm -f /tmp/bpi.amb",

"echo '4.52 0.85 0.74 0 0 1 " +
"3.74 1.13 0.74 0 0 1 " +
"4.52 1.13 0.74 0 0 1 " +
"5.30 1.13 0.74 0 0 1 " +
"3.74 2.13 0.74 0 0 1 " +
"4.52 2.13 0.74 0 0 1 " +
"5.30 2.13 0.74 0 0 1 " +
"3.74 3.13 0.74 0 0 1 " +
"4.52 3.13 0.74 0 0 1 " +
"5.30 3.13 0.74 0 0 1 " +

"' | rtrace -w -af /tmp/bpi.amb -as 512 -ar 64 -aa 0.15 -ab 2 -I+ -h lab.oct | rcalc -e '\$1=(\$1*0.265+\$2*0.670+\$3*0.065)* 179'",

]

Any help would be really appreciated,

Thank you very much

Best regards,

Sokol Dervishi

Thank you very much for your replies. Actually I thought my e_mail was not sent and I apologize for sending it twice.

Best Regards,

Sokol