Add rotated latitude longitude projection to mapping.py

[blaylockbk]

Description Of Changes

Checklist

• Closes metpy/plots/mapping.py >> Unhandled projection: rotated_latitude_longitude #3099
• Tests added
• Fully documented

The Canadian HRDPS model is on a rotated latitude/longitude projection grid. This PR adds the capability for MetPy to parse its projection.

Minimal working example with HRDPS data:

import cartopy.crs as ccrs
import matplotlib.pyplot as plt
from pyproj import CRS
import pygrib
import cfgrib
import xarray as xr
import sys
import metpy

# First, you should download a HRDPS grib2 file from
# https://dd.weather.gc.ca/model_hrdps/continental/2.5km/00/00/
# I grabbed the TMP_AGL-2m file...
FILE = "20230722T00Z_MSC_HRDPS_TMP_AGL-2m_RLatLon0.0225_PT000H.grib2"
ds = xr.open_dataset(FILE)

# Parse the projparams with pygrib, because cfgrib doesn't do this for you
# (see https://github.com/ecmwf/cfgrib/issues/251)
with pygrib.open(str(FILE)) as grb:
    msg = grb.message(1)
    cf_params = CRS(msg.projparams).to_cf()

ds["gribfile_projection"] = None
ds["gribfile_projection"].attrs = cf_params
for var in list(ds):
    if var == "gribfile_projection":
        continue
    ds[var].attrs["grid_mapping"] = "gribfile_projection"

# Ok, now we are ready to check that the changes to metpy/mapping.py worked...
variables = [i for i in list(ds) if len(ds[i].dims) > 0]
ds = ds.metpy.parse_cf(varname=variables)
crs = ds.metpy_crs.item().to_cartopy()

# And plot the data...
ax = plt.subplot(111, projection=crs)
ax.coastlines()
ax.pcolormesh(ds.longitude, ds.latitude, ds.t2m, transform=ccrs.PlateCarree())
ax.set_global()
ax.gridlines()

[blaylockbk]

@erin6541, I know you said you were going to work on this. Here is what I had so far, and it actually did work in my quick test.

[erin6541]

No worries, thanks for letting me know! Glad to hear your test worked.

[dopplershift]

For testing, it's probably good to manually verify that the model data look right when plotted with the generated projection, but for adding to metpy just adding a more simple version in test_mapping.py, like what's there for other projections, should be sufficient.

[dopplershift]

Looks good! Thanks for the contribution!

[dopplershift]

Congrats on your first merged PR to MetPy! 🎉 Hope to see you around in the future!

[blaylockbk]

Thanks! I've been a MetPy user for years. Happy to have finally contributed something.