[python #THI-771303]: Lat/Lon coords for GLM FD grids

Hello! Thanks for reaching out.

I may not be the right person to ask about generally characterizing the extent 
of the un-gridded GLM FOV. However, if you're using the GLM data provided on 
the ABI fixed grid, I can point you in the direction of a few options:

1.) Calculate latitudes and longitudes using the provided projection 
information, but continue to index on the original coordinates. This is what's 
done in your provided article, and we can do this using tools like Cartopy or 
Pyproj. Though, I'm not sure I understand what limitations you ran into here. 
Gridded GLM is provided on the same ABI fixed grid as what's demonstrated 
there, though the particular demonstration uses a CONUS image (1500x2500) and 
not a full disk image (5425x5425).

2.) Compare the gridded GLM to some model output on a different grid (as you 
mention), and look into re-gridding one product onto the grid of the other. 
Cartopy, xarray, and even MetPy have some functionality for this. There are 
also some other tools that might work for your particular use-case, like Satpy 
(on top of Pyresample) or rioxarray (on top of Rasterio), though I'm less 
familiar with these.

Either way, you may end up back at creating a Pyproj `CRS` or `Proj` object 
from the provided projection information in the dataset, which I can help with. 
And, if you're already using MetPy, I can show you a few handy shortcuts to 
this we also provide. Please follow up and let me know what direction you're 
headed with this and I will be glad to help you find a workflow that works! 
Thanks.


All the best,

Drew


> I have spent the past several days working to find the longitude and
> latitude coordinates of GLM gridded product data.  As you know for the full
> disk  there are 5424 x 5424 grid.  As you know,  GLM is just a subset of
> those. A former colleague pointed me to this site: https://makers
> portal.com/blog/2018/11/25/goes-r-satellite-latitude-and-longitude-grid-projection-algorithm.
> I get coordinates using one the codes on the page, but it’s not for the
> full set of grids. This subset spans the GOES R (-+-81) FOV as opposed to
> +-54 of GLM. I am wondering if you know of a way to find the
> coordinates.  Also,  I think there is a way to use the pyoroj library to
> find the coordinates?  I worked with it but no success.  I would ultimately
> like to compare the GLM gridded lightning frequency to the GFDL climate
> model lightning frequency output.


Ticket Details
===================
Ticket ID: THI-771303
Department: Support Python
Priority: Low
Status: Closed
===================
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