[Radiance-general] IES file fun

[Rob Guglielmetti]

I was creating a light source the other day, from an IES file.  Turns 
out this was to be my first encounter with an IESNA LM-63-95-formatted 
file, on a directional, linear fixture.  Well, the first time, using 
Radiance that is.

I ran the *non*-directional downlight file thru ies2rad and then checked 
it in ltview, and it looked like this:

http://www.rumblestrip.org/site-img/rad/linear.jpg

So far so good.

Then I ran the *directional* downlight file thru ies2rad and checked it 
in ltview, and it looked like this:

http://www.rumblestrip.org/site-img/rad/assym.jpg

Eureka!  I have defied physics!  It was after looking at this image that 
I re-checked the ies file, and discovered that it's the LM-63-95 spec. 
This is a problem, because the spec calls for the 0-180 vertical plane 
to be oriented parallel to the lamp axis, whereas it's more common to 
orient it perpendicular.  ies2rad can't even have a check for this, 
because the spec is so loosely written.  This is why checking the 
distribution of my converted luminaires is so important to me, prior 
using them in a calc.  I always did it because I don't trust myself, but 
clearly too much faith in the quality of your input files is also a bad 
thing.

Anyhoo, I simply reversed the length and width values for the luminous 
opening parameters in the ies file, and got this:

http://www.rumblestrip.org/site-img/rad/assym90.jpg

Now, I have a useable fixture, albeit one with a default plan 
orientation that is 90 degrees off from the norm.  I guess I could 
"wrap" the whole thing in an xform file so that I could use it in a 
standard library.

Is there a better way to "correct" a funky IES file for ies2rad? What do 
you all do when you encounter this?

- Rob G.