Handle GeoTransform

[dcherian]

We will need to remove the GeoTransform attribute in assign_index and add a helper function to write it back (similar to .rio.write_transform)

[benbovy]

If we want to avoid relying on rioxarray (i.e., eventually have rasterix as a dependency of rioxarray), we'd also need to vendor .rio.transform as a guess_transform function and/or allow manually passing affine parameters as an input argument of assign_index.

[dcherian]

Alternatively we can add classmethods .from_affine and .from_geotransform to RasterIndex and leave assign_index as the automagic thing that looks for a grid mapping variable, and a GeoTransform attribute on that

[benbovy]

Agreed. If I understand correctly assign_index is a convenient function that might eventually be dropped if rasterix is adopted in libraries like rioxarray, odc-geo, etc.?

[dcherian]

I think that would be preferred. It is certainly just a convenience method.

[weiji14]

Could we define an __affine__ protocol perhaps, where any Python object that has an __affine__ property (returning an affine.Affine object) can then be passed into .from_affine() to get a RasterIndex? I'm thinking of something similar to from_dlpack() that uses objects with a __dlpack__ method.

Asking because I'd like to use rasterix with my library that doesn't depend on rioxarray. I've added some logic to get x- and y-coordinates in weiji14/cog3pio@899d77d, but could delegate that logic to rasterix if there is a stable protocol of some sort.

[dcherian]

Why not just use RasterIndex.from_transform directly?

[weiji14]

RasterIndex.from_transform needs to be called explicitly. I was thinking of something a bit more automagic perhaps, e.g. when the xarray.DataArray undergoes reprojection, the __affine__ property is modified, and the RasterIndex is updated as a result, because it is always dynamically generated from __affine__ rather than having to be set/updated explicitly each time. But maybe this inner state variable already exists somewhere and I just need to read the code 🙂

[dcherian]

#46 deletes the GeoTransform in assign_index, and provides RasterIndex.as_geotransform to grab a string attribute.