Improve description of optical distortion

[dkirkby]

The current fiberloss calculation in bin/fiberloss.py reads data/inputs/throughput/DESI-0347-throughput.txt from this package, and uses the blur values plotted below: This file also includes a column of lateral offset values (also in the plot), but the code uses a fixed value of 0.2" instead.

This issue is to provide a more detailed tabulation of the optical distortion that matches this graph based on ray tracing spots from the "geometric blur" tab of the excel spreadsheet in desi-doc-347-v10:

The main difference is that distortion is tabulated simultaneously in field angle and wavelength, and so captures significant correlations that are missing from the existing platescale.txt table.

I also want to understand how the values in DESI-0347-throughput.txt were calculated from the ray tracing spots.

[dkirkby]

@sbailey Are the data files in this package under change control? What are the logistics of adding a new file?

[dkirkby]

I can now reproduce the spreadsheet plot from numbers provided by Pat Jelinsky:

[sbailey]

We do not have a formal change control procedure for updating desimodel. The guidelines are:

• Every number or file should be traceable to something in DocDB, including the version number of the DocDB entry (we haven't achieved 100% success with this, in particular for some of the numbers in data/targets/targets.dat. But the hardware descriptions should be 100% traceable.
• When possible, hardware data files should come directly from DocDB and not be hand-typed re-interpretations of a table in a Word document. If they require reformating to be more easily machine readable, the version downloaded from DocDB should be in svn desimodel data/inputs/ and then scripts/libraries included in desimodel should convert those into somewhere else (e.g. data/focalplane/ for typical end-user reading.
• Advertising updates through issues like this is good practice. Adding a new file isn't a big deal, but we should advertise any changes to existing files and not just quietly update them.

i.e. in this particular case, let's have Pat/Bobby/Tim add the data file to a DocDB entry, also put it under desimodel data/inputs/ (perhaps in a new data/inputs/focalplane directory?), and provide a script to reformat that somewhat cumbersome ASCII format into an ecsv or FITS table for easier usage downstream. I'll ping the engineers about getting it into DocDB.

[dkirkby]

Just waiting for Pat/Bobby/Tim to add the data file to DESI-347 in DocDB before closing this issue...

[weaverba137]

Did this ever get resolved? We need to know if there are changes to theses files coming that will in turn change the data model.

[dkirkby]

I am reassigning to @sbailey since I have already provided the file so the next step is to knock on some doors.

[weaverba137]

Adding label 'data model' note that fixing this issue will also involve changes to the data model. If that is not the case, please remove the label.