[Radiance-general] indirect/direct photometric

[Greg Ward]

Hi John,

I'll skip for now the question of why you're altering the output of 
ies2rad, and just try to answer your questions, first.

> From: John An <whollycow@mac.com>
>
> 1) The ies2rad command has -di -df -dc and -dm options.  Do I set the 
> units according to the units of the model of my space, or according to 
> the units the photometric data was created?  I am assuming that it 
> would be according to the units of the model of my space (especially 
> since I don't think photometric data is created in inches or 
> centimeters).  However, when I compare the resulting .dat file of 
> using the -df option with the .dat file using -dm, they are identical.

The -d? options affect the geometric dimensions that are output when 
you use the geometry supplied in the ies file.  When you specify your 
own illum sphere with the -i option, it assumes you mean to use the 
units you specify with the -d? option.  All that really changes is the 
first real argument to the brightdata primitive, which scales the vaues 
in the *.dat file appropriately.  The data file itself is (as you 
noted) unchanged.

>
> 2) I used the command:
> ies2rad -df -t white -i .56419 D21998.ies
> I then edited the resulting .rad file to use the lboxcorr function.  
> The file reads as follows:
>
> # ies2rad -df -t white -i .56419
> ...
> !genbox D21998_light D21998.s .141 1.22 .156 \
> | xform -t -.0705 -.61 -.078
>
> Because this file is in meters, I decided to xform the above file 
> using -s 39.3700787 to convert the file to inches (which my model is 
> in).  Is this correct?
>
> The resulting file is:
>
> # xform -s 39.3700787
> # ies2rad -df -t white -i .56419
> ...
>
> 3) However, when I place the resulting illum close to the floor, it is 
> obvious that the light is being emitted is spherical, not linear.  
> There has to be something that I am missing.  Could somebody please 
> inform me?

Are you visualizing the source in rview?  If so, the defaults of -ds 0 
and -dj 0 mean that all light soruces will appear as if eminating from 
a point.  If you set -ds .2 and -dj .6 or so, you should get the result 
you expect.

-Greg