[Radiance-general] rsensor file format

[Axel Jacobs]

I have just measured the spatial response of some of our photocells and 
discovered some rather serious deviations from the standard cosine response.

I am looking at the new rsensor tool to model this response, so I can 
estimate the errors compared to a proper cosine-corrected cell for 
certain configurations. However, the sensor format is not entirely clear 
to me.

a) What are the units in the sensor file? Is it normalised to anything? 
An IES data file, for instance is normalised to 1000lm.

b) What would the sensor file for a normal, cosine corrected illuminance 
meter look like? Does it need to have its maximum at 1.0 for an angle of 
(0,0)?

c) Suppose I wanted to model an illuminance meter that has a correct 
cosine response, but gives a reading twice as high as is should be. 
Would I need to multiply the values from b) by the cube root of 2? Cube 
root because the overall response appears to be proportional to the 
volume contained within the 3d shape of the curves.

d) After a bit of googling around, I found this page:
http://www.lightingresearch.org/programs/nlpip/publicationdetails.asp?ID=916&type=1

Which appears to be the photosensor report referred to on the SPOT web 
site. The NLPIP don't seem to make suggestions about the actual file 
format for electronically transmitting the spacial response (or any 
other photocell characteristics for that matter). I am therefore 
wondering why the rsensor data file is what it is. It seems that the 
standard Radiance data file would have been sufficient to describe the 
sensor's characteristics. What is the advantage of using the SPOT 
format? Why not have a spot2rad (similar to ies2rad) import filter instead?

Example:

The example from the rsensor man page:
degrees   0    90   180  270
0    .02  .04  .02  .04
45   .01  .02  .01  .02
90   .001 .002 .001 .002

As a Radiance dat file, this would look like (I think):
2
0 270 4
0 90 3
.02 .04 .02 .04
.01 .02 .01 .02
.001 .002 .001 .002

Many thanks for sharing your thoughts

Axel