Allow for other common spatial CRS

[forman]

Is your feature request related to a problem? Please describe.

xcube currently does only support spatial grids defined on the spatial CRS EPSG:4326 (Plate Carrée projection).

Many applications require common CRSs based on Transverse Mercator or Azimuthal Lambert projections usually because their cubes are regional and medium to high spatial resolution.

Describe the solution you'd like

The CRS should be encoded in the cube's global attributes following CF conventions. A special attribute proj4_params will contain a PROJ4-compatible parameter string.

• For any CRS that uses decimal degrees as coordinate units, the spatial dimensions and coordinate variables will continued to be named lon and lat.
• For other CRSs, the spatial dimensions and coordinate variables will be named x and y.

Describe alternatives you've considered

On-the-fly reprojection by xcube serve.

Additional context

Urgently required by DCFS project where we need to support Level-1 and Level-2 EO data for multiple high-resolution sensors.

See also

• CF-Conventions on Coordinate Systems
• CF-1.6 <–> WKT/PROJ.4 translation
• Coordinate Systems Worldwide

[AliceBalfanz]

Alternative solution of On-the-fly reprojection by xcube serve implemented in https://github.com/dcs4cop/xcube/releases/tag/v0.11.0