选择数据变量会导致 xarray 中的坐标信息丢失

Question

I wish to subset my xarray Dataset via a list of variable names . However, when I do so, the resultant Dataset no longer has the coordinate reference information, as evidenced by adding the subset as a layer in QGIS.

How can I keep the coordinate reference information after subsetting the original Dataset ?

import xarray as xr

DS = xr.open_dataset("my_data.nc")
bands = ['CMI_C01','CMI_C02','CMI_C03']

# Test does not have coordinate reference information :(
test = DS[bands]

It is apparent that the coordinate reference information is not stored in the .coords attribute, due to the following not working:

# Test still does not have coordinate reference info
test = test.assign_coords(dict(DS.coords))

# When put into QGIS, does not have the CRS
test.to_netcdf("test.nc")

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Where is the CRS stored for xarray Datasets?

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For background, I am using GOES imagery from the public AWS s3 bucket.

This is what the original Dataset looks like:

 Dimensions: (y: 1500, x: 2500, number_of_time_bounds: 2, number_of_image_bounds: 2, band: 1) Coordinates: (3/37) t datetime64[ns] 2017-03-04T08:38:0... * y (y) float32 0.1265... 0.04259 * x (x) float32 -0.07501... 0.06493.47 Attributes: (2/29) naming_authority: gov.nesdis.noaa Conventions: CF-1.7

Answer 1

coordinates in xarray refer to the dimension labels, and have nothing to do with spatial coordinate reference system metadata.

You're looking for xarray Attributes. These can be accessed with .attrs , and you can carry over attributes from one dataset to another with:

test.attrs.update(DS.attrs)

Note that xarray does not explicitly handle CRS information ever , and additionally does not preserve attributes in computations by default. You can change this behavior to keep attributes across computation steps by default with:

xr.set_options(keep_attrs=True)

See the FAQ section: What is your approach to metadata? for more information. Also see the docs on Data Structures for more detail on the various xarray objects.