[Radiance-general] computing illuminance across a grid

[Rob Guglielmetti]

THanks again for the advice.  Replies to the replies below:

On 22 May 2002, at 22:33, Roland Schregle wrote:
> For your single measurement you'd use:
> 
> echo 60 60 30 0 0 1 | rtrace -h -I scene.oct
> 
> Ain't UNIX fun? :^)

It's getting more fun all the time, as I move out of the 
"complete idiot" category and into the "pathetic novice" 
category, unix-wise.  Greg's tip about OSX and his pre-
compiled binaries have really helped me get up & running 
on a unix-based Radiance learning trip, and this list is 
now helping too.  I appreciate it. 

On 23 May 2002, at 8:31, Phillip Greenup wrote:

> Do you have rillum?  if you have rillum, it makes this
> process somewhat easier.
> 
> 1. create an input file with a pile of measuring points and
> positions, similar to your 60 60 30 0 0 1.  cnt and rcalc
> can help in the creation of this file, but it can also be
> done in any text editor, or spreadsheet and exported as an
> ascii file.  use one line per measuring point. 2. rillum
> [rtrace options] octree < infile > outfile

Well, that sounds like a useful little program.  I don't have 
this.  Where do I get it??  I am using pre-compiled 
binaries for OS X, created by Greg Ward.  Most of the 
other stuff is there, but not glrad or this rillum.  

I'd compile the source myself, but I get errors all the time, 
both on OSX and Linux. (Yes, I installed Yellow Dog Linux 
2.2 on my Powerbook.  I couldn't help myself.)  And at the 
moment I'm far more interested in using Radiance than 
administering a unix system, so I guess I'm cheating a bit 
by using precompiled binaries.  =8-)

> the output file then contains a column of illuminances
> corresponding to the measuring points and orientations
> defined in the input file.  if you wish, you can then use
> lam to put the input and output files together in a table.

On 22 May 2002, at 14:21, Greg Ward wrote:
> a better example for a grid
> of 15 by 30 points spread in a 10x20 room and 2.5 feet 
off
> the floor with a half foot margin on each side would be:
> 
> % cnt 15 30 | rcalc -e
> '$1=(10-.5)/(15-1)*$1;$2=(20-.5)/(30-1);$3=2.5' \
>  -e '$4=0;$5=0;$6=1' | rtrace -I -h [options] octree \
>  | rcalc -e '$1=179*(.265*$1+.670*$2+.065*$3)' > 
output.dat

Thanks Greg.  Since I don't have rillum (yet) this works 
well.  I typed this up in a text file, and did a chmod 755 on 
it, so I can call that whole mess with one filename.  
(Roland- fun with unix! ;-)) However, my problem now is 
that it recorded values of zero!  The scene is not dark.  I 
double checked the inputs.  It's still zero.  My room is 
12'x14', but I'm working in inch units, so my code went 
like this:

cnt 15 30 | rcalc -e 
$1=(144-6)/(15-1)*$1;$2=(168-6)/(30-1);$3=30' \
-e '$4=0;$5=0;$6=1' | rtrace -I -h [options] octree \
  | rcalc -e '$1=179*(.265*$1+.670*$2+.065*$3)' > 
output.dat

(note: the first two lines above are on one line in the 
command file.  Damn emailer.)

This should place a grid of "light meters" facing up, 2'6" 
off the floor, right?  Why is my scene illuminance reading 
zero??  It's a daylit space!  When I load a pic into ximage 
and pick a point & press return, I get radiance values of 
.298, .428, on the floor.  Hmmm...

Also, I'm wondering how rtrace gets its information, since 
it's working with an octree, not a pic file.  I don't 
understand how it can compute irradiance so fast unless 
it somehow works with a pic file and/or the cached 
ambient file.  Along those lines, if you want accurate 
values for a room, and only have generated a pic of, say, 
the north elevation, how accurate are the vertical 
illuminance values on the south elevation?  

         ====================
 Rob Guglielmetti <rpg777@earthlink.net>
    http://home.earthlink.net/~rpg777