issues: 1194993450

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
1194993450 I_kwDOAMm_X85HOicq 6448 Writing GDAL ZARR _CRS attribute not possible 15717873 closed 0     12 2022-04-06T18:37:34Z 2022-09-04T14:21:13Z 2022-06-03T18:48:47Z NONE      

What is your issue?

Related to https://github.com/pydata/xarray/issues/6374

Writing a ZARR which is compatible with GDAL conventions using xarray.Dataset.to_zarr requires all the data variables to have a _CRS attribute which contains the Spatial Reference System encoding (SRS). This _CRS attribute itself is a dict in which the SRS is encoded in at least one of these keys: wkt, url, projjson

Because attribute values can't be dictionaries during serialization, it does not seem possible to write GDAL compatible zarrs using xarray.

Example:

lets assume we have a Dataset ds like this:

<xarray.Dataset> Dimensions: (Y: 180, X: 360) Coordinates: * X (X) float64 -179.5 -178.5 -177.5 -176.5 ... 176.5 177.5 178.5 179.5 * Y (Y) float64 89.5 88.5 87.5 86.5 85.5 ... -86.5 -87.5 -88.5 -89.5 Data variables: Band1 (Y, X) uint16 0 0 0 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0 0 0 Band2 (Y, X) uint16 0 0 0 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0 0 0 Band3 (Y, X) uint16 0 0 0 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0 0 0

lets also assume we want to encode the _CRS as wkt like so:

python wkt = 'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AXIS["Latitude",NORTH],AXIS["Longitude",EAST],AUTHORITY["EPSG","4326"]]'

(encoding the _CRS in any of the other 2 formats results in the same problem at the end)

Setting the attributes of each data variable:

``` python attributes = { "_ARRAY_DIMENSIONS": ['Y', 'X'], "_CRS": {"wkt": wkt}, "AREA_OR_POINT": 'Area', }

for data_var in ds.data_vars: ds[data_var].attrs = attributes ```

no problem so far, ds.Band1.attrs results in:

python { "_ARRAY_DIMENSIONS": ["Y", "X"], "_CRS": { "wkt": 'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AXIS["Latitude",NORTH],AXIS["Longitude",EAST],AUTHORITY["EPSG","4326"]]' }, "AREA_OR_POINT": "Area", }

the problem now occurs with writing the dataset using:

python ds.to_zarr("test.zarr", consolidated=True)

``` TypeError: Invalid value for attr '_CRS': {'wkt': 'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AXIS["Latitude",NORTH],AXIS["Longitude",EAST],AUTHORITY["EPSG","4326"]]'}.

For serialization to netCDF files, its value must be of one of the following types: str, Number, ndarray, number, list, tuple ```

 
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