[Radiance-general] rsensor file format
Axel Jacobs
a.jacobs at londonmet.ac.uk
Sun Oct 11 06:36:32 PDT 2009
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 curve.
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
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