[Radiance-general] rsensor file format

[Scheib, Jennifer]

Hi Axel,

This is a timely question. Zack and I are going to give a review of rsensor at the Radiance Workshop and I need to refresh on these issues anyway. SPOT includes spatial sensitivity files for the sensors tested in the NLPIP report you referenced, so you can download the program and take a look at the files and implementation - if you haven't already. 

Answers to your specific questions:

a) and b) For the comparison you want to do, the values would be relative sensitivity - relative to a cosine response with maximum of 1 as you described. This would allow the result with a cosine distribution to be computed as illuminance depending on parameters and the result with any other file to be "signal" relative to illuminance. For the NLPIP report, the zero azimuthal direction (view up vector) coincides with a prominent feature on the photocell housing, such as an arrow. This is probably not clear for all sensors tested.

c)I might be misunderstanding the question but you should just multiply the sensitivity values by 2 if you want double the signal. This will increase the volume by 2^3 but is not used to scale the sensitivity file. 

remainder) Good point about file format. I think the answer is that Greg developed rsensor for AEC/SPOT and AEC received the sensitivity files from the LRC in the format shown in the manpage. So it is not really a SPOT format as much as it is testing output. Ian Ashdown is proposing an extension to IESNA LM-74-05 to give a formal definition for photosensor test reporting. I am unsure of the status of this right now. Assuming this gets published then maybe a parallel or extension to ies2rad makes sense. Other comments, Zack or Greg? 


I hope this is helpful,

Jennifer

-----Original Message-----
From: radiance-general-bounces at radiance-online.org [mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Axel Jacobs
Sent: Sunday, October 11, 2009 4:37 PM
To: radiance-general at radiance-online.org
Subject: [Radiance-general] rsensor file format

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

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