[pmaciel]

Description

eckit::geo for all supported grids, extended gridSpec, projString and the iterator support for all varieties of scanning modes. eckit::geo is not patched to reproduce legacy issues, some newly discovered; where eccodes differs, the tests say so. Changes:

Gaussian grids, as encoded (GribToSpec)

• Angles are compared to the precision they are encoded with (angular_precision, including fractions). There are no hardcoded tolerances.
• The first/last latitudes and longitudes are snapped to the grid (both latitudes and longitudes) within that precision. For example, an F1280 sub-area encoded with longitudeOfFirstGridPointInDegrees=65.039062 (truncated) gets its first column again.
• Regular Gaussian grids of any number of longitudes: ni, from the encoded increment, unless 4N (this last one is not fully well handled in eccodes or mir).
• pl is validated (every entry positive). A regional pl is placed on the global latitudes by Gaussian latitude, in either latitude direction.
• The east longitude fix for global reduced grids also applies to reduced_rotated_gg, reduced_stretched_gg and reduced_stretched_rotated_gg.

Projected and space_view grids, projString

• albers, lambert, lambert_lam, lambert_azimuthal_equal_area, mercator, polar_stereographic and space_view grids are described on the projection plane:
  • x/y ranges, in grid lengths;
  • a false easting/northing placing the first grid point at (0, 0), to millimetres (for round-off);
  • the projection from (x, y), as PROJ aea, lcc, laea, merc, stere and geos;
  • the message figure (spheres and ellipsoids, including GRIB1 earthIsOblate).
• Scanning modes, including alternativeRowScanning and jPointsAreConsecutive, are the spec order.
• With env ECCODES_ECKIT_GEO=1 or ECCODES_ECKIT_GEO=2, projString comes from eckit::geo. It builds the projection only, so the grid geometry doesn't need to be valid. A buffer too small reports the length needed.

Iterator

• With env ECCODES_ECKIT_GEO=1, eckit::geo iterates these grid types:
  • regular_ll, rotated_ll and reduced_ll;
  • regular_gg, rotated_gg, reduced_gg and reduced_rotated_gg;
  • healpix and unstructured_grid;
  • the projected and space_view types above.
• Grids with alternativeRowScanning are no longer excluded.
• The grid is checked against the message: a numberOfDataPoints different from the grid size is an error ("Wrong number of points"), both in the iterator and in gridSpec. Reduced Gaussian sub-areas encoded as PRODGEN/LIBEMOS did (rows rounded differently) are an example.
• Memory leak fixed on creating the (geo) iterator on errors.

With env ECCODES_ECKIT_GEO=0 (the default), the iterator and projString are unchanged. Only gridSpec (always by eckit::geo) changes: its values for the grids above, and the error for a message whose number of points isn't its grid's.

Tests

• grib_geo_iterator:
  • Compares eckit::geo grid points to the eccodes iterator, message by message, in the eccodes iterator order.
  • Covers regular, reduced, rotated and Gaussian sub-areas, HEALPix, projected and space_view windows, alternating rows, the F1280 longitude precision, and a single rotated point as an example.
  • Not compared, with the reason printed: Lambert grids scanning j- (the eccodes iterator assumes latitudes increase from the first grid point, GRIB-405), and rotated_gg (the eccodes iterator does not unrotate it).
• grib_eckit_geo_proj_string: projString (classical) compared to the PROJ string of the eckit::geo projection, and the projection round trip from its spec.
• grib_eckit_geo_projections: for each projected and space_view grid (examples of operational grids, and the test data), checks:
  • gridSpec and the projection spec;
  • projString with env ECCODES_ECKIT_GEO=0, 1 and 2;
  • the first, second and last points.
• Test messages of projected and lat/lon grids built from samples set their grid keys explicitly, rather than relying on the sample's grid.
• Existing tests check the env ECCODES_ECKIT_GEO value where eckit::geo behaves differently:
  • grib_grid_polar_stereographic: an oblate Earth is supported;
  • grib_grid_mercator: error message;
  • grib_grid_lamb_az_eq_area: longitudes modulo 360;
  • grib_change_scanning: alternating rows are iterated;
  • grib_iterator: the legacy reduced Gaussian sub-area is an error.

Related changes

• eckit (eckit::geo): needs eckit::geo: scanning orders, projections, search, caches and gridspec fixes eckit#374. That PR brings projections as PROJ, regular_xy grids, Albers on ellipsoids, scanning orders including alternating rows, Gaussian grids of any ni, and single-value ranges.

Please test with the matching eckit version.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.70%. Comparing base (d9d0d83) to head (914db71).

Additional details and impacted files

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##           develop     #606   +/-   ##
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  Coverage    87.70%   87.70%           
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  Files          860      860           
  Lines        64257    64257           
  Branches     11450    11450           
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  Hits         56358    56358           
  Misses        7899     7899           

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