[Radiance-general] Intentity_of_pixel

[Rob Guglielmetti]

Faouzi Djafi wrote:

> I want to post the value of illuminance pixel (intentity of pixel) on 
> the same point in the two pictures.

> can you say to me what's the good way to do this?

The program rtrace can compute illuminance at a specific point; this is 
typically what I use when I want to compare scenarios or capture 
daylighting data for a space.  You can feed rtrace a text file with a 
whole series of points (one per line) and it will calculate the 
illuminance for each one in turn.

For example, create a file with lines like this:

0 0 0 0 0 1
0 0 10 0 0 -1

That file describes two "virtual light meters", one on the floor at 
0,0,0 looking up.  The other is located ten units above it, looking 
down, just as an example.  You'd feed these to rtrace like this:

rtrace [options] -I scene.oct < points.txt > values.txt

points.txt is the file with all your points you'd like to evaluate, and 
then rtrace saves the computed illuminance values in values.txt.

Of course, you'd then have to manually paste in some sort of graphic tag 
indicating the illuminance into a completed .pic file, if you wish to 
have an image with the illuminance.  I'm sure there's a way to have 
Radiance do it for you, but in general I use rtrace to spit out a whole 
series of numbers, which I summarize in tabular form.  I'll usually just 
do one image which serves as a reference key to all the calculation 
points.  This method works for me; YMMV.

----

      Rob Guglielmetti

e. rpg@rumblestrip.org
w. www.rumblestrip.org