Bugfix: Fix support for NSIDC v4 Climate Data Record data on Polar Stereographic grids in CF-compliant NetCDF files

[JohnHalleyGotway]

Describe the Problem

This issue was raised in the third topic of the dtcenter/METplus#2312 discussion. Please see this comment for details.

Expected Behavior

While the sample NetCDF file follows the CF-convention, MET is not handling it properly. There are 2 issues to be addressed.

1. The projection x and y dimensions are not defined by coordinate variables, but are identified using the expected standard_name attribute:

	float xgrid(x) ;
		xgrid:standard_name = "projection_x_coordinate" ;
	float ygrid(y) ;
		ygrid:standard_name = "projection_y_coordinate" ;

Renaming to use coordinate variables x(x) and y(y) does enable MET to continue on to the next problem, described below. The task is to inspect the CF-conventions to determine whether or not the use of coordinate variables is required here. If not, generalize the code to inspect all 1-d variables rather than just coordinate variables.

2. MET does not properly parse the polar stereographic grid definition from these files. See below.

Environment

Describe your runtime environment:
1. Machine: Mac Laptop
2. OS: MacOS
3. Software version number(s): Tested using the main_v11.1 branch of MET

To Reproduce

Describe the steps to reproduce the behavior:
1. Download this file:
seaice_conc_monthly_sh_202208_f17_v04r00.nc.gz
2. Rename to coordinate variables:

ncrename -v xgrid,x -v ygrid,y \
seaice_conc_monthly_sh_202208_f17_v04r00.nc \
seaice_conc_monthly_sh_202208_f17_v04r00_MOD.nc

3. Run plot_data_plane at verbosity level 4:

MET-main_v11.1/bin/plot_data_plane \
seaice_conc_monthly_sh_202208_f17_v04r00_MOD.nc plot.ps \
'name="cdr_seaice_conc_monthly"; level="(0,*,*)";' -v 4
...
DEBUG 4: Grid information:
DEBUG 4:    Projection: Stereographic
DEBUG 4:    Nx: 316
DEBUG 4:    Ny: 332
DEBUG 4:    IsNorthHemisphere: false
DEBUG 4:    Lon_orient: -180.000
DEBUG 4:    Bx: nan
DEBUG 4:    By: nan
DEBUG 4:    Alpha: inf

The Bx, By, and Alpha values all have problems.

Relevant Deadlines

List relevant project deadlines here or state NONE.

Funding Source

Define the source of funding and account keys here or state NONE.

Define the Metadata

Assignee

• Select engineer(s) or no engineer required
• Select scientist(s) or no scientist required

Labels

• Select component(s)
• Select priority
• Select requestor(s)

Projects and Milestone

• Select Organization level Project for support of the current coordinated release
• Select Repository level Project for development toward the next official release or add alert: NEED CYCLE ASSIGNMENT label
• Select Milestone as the next bugfix version

Define Related Issue(s)

Consider the impact to the other METplus components.

• METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy
  No impacts.

Bugfix Checklist

See the METplus Workflow for details.

• Complete the issue definition above, including the Time Estimate and Funding Source.
• Fork this repository or create a branch of main_<Version>.
  Branch name: bugfix_<Issue Number>_main_<Version>_<Description>
• Fix the bug and test your changes.
• Add/update log messages for easier debugging.
• Add/update unit tests.
• Add/update documentation.
• Push local changes to GitHub.
• Submit a pull request to merge into main_<Version>.
  Pull request: bugfix <Issue Number> main_<Version> <Description>
• Define the pull request metadata, as permissions allow.
  Select: Reviewer(s) and Development issue
  Select: Organization level software support Project for the current coordinated release
  Select: Milestone as the next bugfix version
• Iterate until the reviewer(s) accept and merge your changes.
• Delete your fork or branch.
• Complete the steps above to fix the bug on the develop branch.
  Branch name: bugfix_<Issue Number>_develop_<Description>
  Pull request: bugfix <Issue Number> develop <Description>
  Select: Reviewer(s) and Development issue
  Select: Repository level development cycle Project for the next official release
  Select: Milestone as the next official version
• Close this issue.