Fix "Unit conversion when equivalency needed breaks contours in cubeviz"

[pllim]

Description

This pull request is to unit conversion when equivalency needed breaks contours in cubeviz. Unskips a test added in #3204 .

Probably no need for change log since this is patching unreleased feature, I assume.

Change log entry

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[pllim]

Somehow this one test makes 2 very different tracebacks. Funky.

x = array([0., 0., 0., 0., 0., 0., 0.])

    def f_la_from_f_nu(x):
>       return x / (wav.to_value(si.AA, spectral()) ** 2 / c_Aps)
E       ValueError: operands could not be broadcast together with shapes (7,) (3001,)

E       astropy.units.core.UnitConversionError: 'erg / (Hz s cm2 pix2)' and 'erg / (Angstrom s cm2 pix2)' are not convertible

[pllim]

The original exception reported in JIRA also produces ValueError: operands could not be broadcast together with shapes (7,) (3438,) (one of the exceptions from unskipped test)

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.45%. Comparing base (fc88465) to head (45aa120).

Files with missing lines	Patch %	Lines
...specviz/plugins/unit_conversion/unit_conversion.py	85.71%	2 Missing ⚠️
...imviz/plugins/aper_phot_simple/aper_phot_simple.py	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3207      +/-   ##
==========================================
- Coverage   88.46%   88.45%   -0.01%     
==========================================
  Files         125      125              
  Lines       18677    18699      +22     
==========================================
+ Hits        16522    16541      +19     
- Misses       2155     2158       +3     

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[pllim]

In a nutshell, the way all this stuff is set up, it goes through the glue unit conversion machinery that has no access to app data (like cube slice or spectral axis). So the least painful way I can think of is to define the equivalencies (again) where things are broken (as far as this JIRA ticket is concerned). For the background unit conversion, I cannot find any existing equivalencies that would work on the / pix2 stuff so I put in a hack to remove it. Ideas welcome.

[pllim]

I actually not sure if grabbing [0] is entirely correct but I also don't know what is really happening when values are only an array of 7 elements. I think that is the downsampled version from the viewer but really hard to tell for sure.

[cshanahan1]

can you check if this is the case for steradian as well? i believe you cant convert flux/sr <> flux/sr if there is a u.spectral_density equivalency needed.

you could also leave a note here to pass this through utils.flux_conversion eventually - i'm working on generalizing this function to handle cases like this and it might simplify this code if we want to swap it later on

[pllim]

I think steradian is already covered by existing equivalencies combo because steradian is a recognized physical unit in astronomy, whereas pixel is very much tied to instrumentation and not well defined in astropy.units. CI passes without such treatment for u.sr. Unless you mean somehow the existing test suite does not cover the steradian case already?

jdaviz/jdaviz/utils.py

Line 519 in fc88465

def _eqv_pixar_sr(pixar_sr):

[pllim]

Ah, I see the test I unskipped is about Cubeviz unit conversion plugin only. And this code is inside aperture photometry. I can think of how I can expand your test case to go through this line as well tomorrow, maybe. 🤔