Focus scan analysis

[julienguy]

Add script desi_focus to analyse a sequence of focus scans.

• preprocess exposures
• detect spots, fit gaussian per spot per exposure and save as csv table
• merge tables, bin or match values of given fiber/wavelength
• best fit focus for each bin or spot
• fit best focus plane as a function of xccd , yccd
• convert to gauge offsets for the 3 screws adjusting the cryostat piston and tilt

Example for SM10 red camera

desi_focus -i /global/homes/j/jguy/data/20200109/0003924{1,2,3,4,6,7,8}/desi-000*.fits.fz -o . --cam r1 --offsets=-150,-100,-50,0,50,100,150 --gauges=60.750,60.946,61.084 --plot --testslit

Average best fit piston

Sigma values for best exposure (note some fibers are off in test slit)

Best focus per spot (wavelength, fiber) and best plane fit

Comparison with analysis of AMU team for some spectrographs

Spec  AMU  This_work    Difference
------------------------------------------------------------------------
    TOP LEFT RIGHT TOP LEFT RIGHT TOP LEFT RIGHT
SM7 60.601 61.451 61.597 60.585 61.479 61.583 -0.016 0.028 -0.014
SM8 60.698 60.927 60.936 60.699 60.928 60.927 0.001 0.001 -0.009
SM9 60.885 61.065 61.259 60.886 61.070 61.237 0.001 0.005 -0.022
SM10 60.728 61.035 61.202 60.737 61.034 61.177 0.009 -0.001 -0.025

[sbailey]

Overall, looks good, though please add docstrings for all functions for long term maintainability, including defining the return values of functions.