Add support for Gaussian grids in the vx_data2d_python library.

[JohnHalleyGotway]

Describe the Problem

This issue arose when Tina Kalb was using python-embedding to pass MET version 9.1 gridded data input on a Gaussian grid. This resulted in the following runtime error:
ERROR :
ERROR : grid_from_python_dict() -> bad projection type: "Gaussian"
ERROR :

While MET version 9.1 does support data on Gaussian grids, support for this projection was not added to the vx_data2d_python library. It is noticeably absent from the list of projections here:

MET/met/src/libcode/vx_data2d_python/grid_from_python_dict.cc

Line 31 in 2c9ae44

static const char rotated_latlon_string [] = "Rotated LatLon";

Expected Behavior

Use the attached data to run the following command:

plot_data_plane PYTHON_NUMPY plot.ps 'name="read_era_nc.py ei.oper.an.pl.regn128sc.1979010100.miller369109.nc";'

read_era_nc.py.txt
ei.oper.an.pl.regn128sc.1979010100.miller369109.nc.txt

This should run without error and correctly handle the Gaussian grid.

Environment

Describe your runtime environment:

1. Machine: Cheyenne and replicated on Mac
2. Using met-9.1.

To Reproduce

Describe the steps to reproduce the behavior:

1. Run the command listed above using MET version 9.1.

Relevant Deadlines

None

Funding Source

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Define the Metadata

Assignee

• Select engineer(s) or no engineer required: John Halley Gotway
• Select scientist(s) or no scientist required: Tina Kalb should review the PR.

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Define Related Issue(s)

Consider the impact to the other METplus components.

• METplus, MET, METdatadb, METviewer, METexpress, METcalcpy, METplotpy
  No other imacts.

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[JohnHalleyGotway]

I ran pcp_combine to convert an existing Gaussian GRIB1 file to NetCDF and checked the output attributes:
:Projection = "Gaussian" ;
:lon_zero = "0.000 degrees_east" ;
:nx = "512" ;
:ny = "256" ;

Based on this, I'll setup the code to look for:
'type' : 'Gaussian',
'lon_zero' : 0.0,
'nx' : 512,
'ny' : 256,

For this to work, I had to change Tina's camel-case "Nx" and "Ny" to lower-case "nx" and "ny". This is unfortunate. I would be nice to have a case-insensitive lookup option instead of requiring the case to be exactly correct.

[JohnHalleyGotway]

With this change, MET is able to read/plot this data correctly:

plot_data_plane PYTHON_NUMPY plot.ps 'name="read_era_nc.py ei.oper.an.pl.regn128sc.1979010100.miller369109.nc";'

[CPKalb]

Hi John: I actually tried running my data this way, but pcp_combine crashed on some (a total of 88) of my input GRIB1 files. This crash makes no sense, since all of the grib1 files ran through regrid_data_plane effectively. But, this is what motivated me to try reading the data in through python. What's going on here is that I'm trying to duplicate someone's results for my blocking case. The grib1 files contain more decimal points (5) than the 1-2 stored in the netCDF files. The person who originally did this started with netCDF. So, I don't know if the differences I'm seeing in my output are due to the different precision or something else. I can provide one of the grib1 files that crashed in pcp_combine if that's helpful. Tina

…

On Wed, Sep 2, 2020 at 3:08 PM johnhg ***@***.***> wrote: With this change, MET is able to read/plot this data correctly: plot_data_plane PYTHON_NUMPY plot.ps 'name="read_era_nc.py ei.oper.an.pl.regn128sc.1979010100.miller369109.nc";' [image: plot] <https://user-images.githubusercontent.com/21087144/92036836-12ecaa80-ed2e-11ea-9ed4-984fe71c440d.png> — You are receiving this because you were assigned. Reply to this email directly, view it on GitHub <#1477 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFJHD4U5XXMUYDFADRDJDU3SD2X4JANCNFSM4QTW7YAQ> .

-- ************************************************* Christina Kalb Associate Scientist National Center for Atmospheric Research 3450 Mitchell Lane Boulder, CO 80301 kalb@ucar.edu 303-497-2819 ************************************************* My working day may not be your working day. Please do not feel obliged to reply to this email outside of your normal working hours.