New Xarray accessor for DEMs through xDEM

Hi all,

(Co-opening in rioxarray due to the raster nature of the accessor: https://github.com/corteva/rioxarray/issues/687)

Following what is asked in the doc, I'm letting you know that we intend to write an xarray accessor to enable functions specific to digital elevation models in our package xDEM! 🙂

The accessor would mirror all the functionalities we have (and future ones):

• Vertical CRS transformation (not yet supported by rasterio so built on top of pyproj directly, would build on top of rioxarray in the accessor),
• Terrain attributes (I see a bit of overlap with xarray-spatial in "Surface": https://xarray-spatial.org/user_guide/surface.html for some of these; we have more published versions which can be parametrized, so I guess that's OK? I could start a discussion there to coordinate future development),
• 3D registration,
• Terrain corrections,
• Error estimation and propagation (may be moved to GeoUtils as not specific to DEMs but all rasters, see https://github.com/pydata/xarray/issues/8041; eventually using ObsArray).

I was thinking of using the accessor name dem, e.g.: ds.dem.to_vcrs(), ds.dem.profile_curvature() or ds.dem.coregister(). I didn't catch any overlap with other efforts. Would that work fine?

Thanks! (and for the great work on xarray!)

Begin with the linked rioxarray issue and the proposed xDEM functionality list, including vertical CRS transformation, terrain attributes, registration, and corrections. Done would require an agreed accessor scope and API for xarray, but this issue names no implementation files or tests and remains a broad design proposal.