issues: 348081353

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348081353 MDU6SXNzdWUzNDgwODEzNTM= 2348 Should the transform attribute be a six-element or nine-element tuple when reading from rasterio? 296686 closed 0     2 2018-08-06T21:03:43Z 2018-08-13T22:33:54Z 2018-08-13T22:33:54Z CONTRIBUTOR      

My basic question is whether XArray should be storing the rasterio transform as a 6-element tuple or a 9-element tuple - as there seems to be a mismatch between the documentation and the actual code.

The documentation at https://github.com/pydata/xarray/blob/7cd3442fc61e94601c3bfb20377f4f795cde584d/xarray/backends/rasterio_.py#L164-L170 says you can run the following code:

from affine import Affine da = xr.open_rasterio('path_to_file.tif') transform = Affine(*da.attrs['transform'])

This takes the tuple stored in the transform attribute and uses it as the arguments to the Affine class. However, running this gives an error: TypeError: Expected 6 coefficients, found 9.

If you look at the code, then this line in the open_rasterio function sets the transform attribute to be a 6-element tuple - the first 6 elements of the full Affine tuple: https://github.com/pydata/xarray/blob/7cd3442fc61e94601c3bfb20377f4f795cde584d/xarray/backends/rasterio_.py#L249. However, about twenty lines later, another chunk of code looks to see if there is a transform attribute on the rasterio dataset and if so, sets the transform attribute to be the full Affine tuple (that is, a 9-element tuple): https://github.com/pydata/xarray/blob/7cd3442fc61e94601c3bfb20377f4f795cde584d/xarray/backends/rasterio_.py#L262-L268

Thus there seems to be confusion both within the code and the documentation as to whether the transform should be a six-element or nine-element tuple.

Which is the intended behaviour? I am happy to submit a PR to fix either the code or the docs or both.

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.6.final.0 python-bits: 64 OS: Darwin OS-release: 16.7.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: en_GB.UTF-8 xarray: 0.10.8 pandas: 0.23.4 numpy: 1.14.2 scipy: 1.1.0 netCDF4: 1.4.0 h5netcdf: 0.6.1 h5py: 2.8.0 Nio: None zarr: None bottleneck: 1.2.1 cyordereddict: None dask: 0.18.2 distributed: 1.22.1 matplotlib: 2.2.2 cartopy: None seaborn: None setuptools: 40.0.0 pip: 18.0 conda: None pytest: None IPython: 6.5.0 sphinx: None 
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