Accessing COG overviews with read_rasterio

[rsignell-usgs]

It's considered best practice to create cloud-optimized geotiff (COG) with overviews, which are essentially copies of the dataset at different resolutions to allow fast representation at different scales.

It would be nice if we could pick a specific overview using xr.read_rasterio, perhaps by just an additional parameter on the call, like xr.read_rasterio(url, overview=512) or something.

Currently we need to use Rasterio to find out what the overlays are, for example:

url = 'https://esip-pangeo-uswest2.s3-us-west-2.amazonaws.com/sciencebase/Southern_California_Topobathy_DEM_1m_cog.tif'
src = rasterio.open(url, 'r')
[src.overviews(i) for i in src.indexes]

which results in:

[[4, 8, 16, 32, 64, 128, 256, 512, 1023]]

See the notebook here for the hack workaround to extract an overlay from COG:
https://nbviewer.jupyter.org/gist/rsignell-usgs/dc4cf94fae97d085f6f2b9b896ec5336

[dcherian]

That kwarg looks good to me. Can you send in a PR?

[scottyhq]

@dcherian I was just revisiting a use-case for this and realized xr.open_rasterio() does not take **kwargs.
http://xarray.pydata.org/en/stable/generated/xarray.open_rasterio.html#xarray.open_rasterio

I think this would be easy to implement because a while back rasterio implemented a keyword argument so that you can do rasterio.open(path, overview_level=3)
rasterio/rasterio#1504

So is this just a matter of accepting kwargs in xr.open_rasterio() and passing them through?

xarray/xarray/backends/rasterio_.py

Line 241 in 4aa7622

manager = CachingFileManager(rasterio.open, filename, lock=lock, mode="r")

As seems to be done here for example:

xarray/xarray/backends/h5netcdf_.py

Line 164 in cc271e6

manager = CachingFileManager(h5netcdf.File, filename, mode=mode, kwargs=kwargs)

[dcherian]

looks right to me. Let's try it!