netCDF4 interoperability

[christine-e-smit]

Using python NetCDF4 library version 1.6.2, I was able to load a zarr store.

Data used: #36

The "netCDF-like" zarr store could be opened. The "geotiff-like" zarr store could not be opened.

To reproduce:

1. Download and unzip the netCDF-like zarr store.
2. Open in python using the nczarr syntax:

import netCDF4
nc = netCDF4.Dataset('file:///YOUR/PATH/TO/GLDAS_NOAH025_3H.zarr#mode=nczarr,zarr')

[christine-e-smit]

@ethanrd - any idea why the "geotiff-like" zarr store caused python to crash for me? I looked at the metadata, I can't immediately see what the issue is. It does load just fine with xarray.

>>> import netCDF4
>>> netCDF4.Dataset('file:///PATH/planet-fusion.zarr#mode=nczarr,zarr')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "src/netCDF4/_netCDF4.pyx", line 2469, in netCDF4._netCDF4.Dataset.__init__
  File "src/netCDF4/_netCDF4.pyx", line 2028, in netCDF4._netCDF4._ensure_nc_success
OSError: [Errno -137] NetCDF: NCZarr error: 'file:///PATH/planet-fusion.zarr#mode=nczarr,zarr'

[christine-e-smit]

@ethanrd - Can I create a new zarr store using the netCDF4 library? The documentation for the Dataset class (https://unidata.github.io/netcdf4-python/#netCDF4.Dataset) indicates that you need to specify the data format, but I don't see anything with 'zarr' as an option. Just because, I tried NC_ZARR and NCZARR, but neither of those worked.

[christine-e-smit]

@ethanrd - One more question! It looks as though the NetCDF library is having trouble with compression.

import netCDF4
nc = netCDF4.Dataset("file:///YOUR/PATH/GLDAS_NOAH025_3H.zarr#mode=nczarr,zarr")
nc["Tair_f_inst"][0][401][238]

gives the error:

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
Cell In[33], line 1
----> 1 nc["Tair_f_inst"][0][401][238]

File src[/netCDF4/_netCDF4.pyx:4972](http://localhost:8888/netCDF4/_netCDF4.pyx#line=4971), in netCDF4._netCDF4.Variable.__getitem__()

File src[/netCDF4/_netCDF4.pyx:5930](http://localhost:8888/netCDF4/_netCDF4.pyx#line=5929), in netCDF4._netCDF4.Variable._get()

File src[/netCDF4/_netCDF4.pyx:2034](http://localhost:8888/netCDF4/_netCDF4.pyx#line=2033), in netCDF4._netCDF4._ensure_nc_success()

RuntimeError: NetCDF: Filter error: undefined filter encountered

I'm almost certain that I talked with someone at Unidata about this more than a year ago, but I can't find where I had the conversation.