Gdt40 save#813
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## main #813 +/- ##
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- Coverage 90.05% 89.70% -0.36%
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Lines 2564 2680 +116
Branches 420 440 +20
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…d dim needs a dimcoord.
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Update 2026-07-21
Not implemented:
Still to-do:
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Pull request overview
Adds experimental support for saving GRIB2 reduced Gaussian grids (GDT 3.40) by recording the original grid template on load and using it to select an appropriate ecCodes sample/template during save.
Changes:
- Record GRIB2 grid template number on load via a new
TEMPLATE_RECORDcontrol and attach agaussian_gridDimCoord for reduced Gaussian grids. - Add save-rule logic for GDT 3.40 (including detection + template 40 writer) and update the save pipeline to select a reduced-gg sample.
- Update/extend unit + integration tests and expected CML outputs to include the new
gaussian_gridcoordinate and round-trip behavior.
Reviewed changes
Copilot reviewed 10 out of 10 changed files in this pull request and generated 9 comments.
Show a summary per file
| File | Description |
|---|---|
src/iris_grib/_save_rules.py |
Adds GDT 3.40 detection and encoding logic; threads chosen x/y coords through save rules. |
src/iris_grib/_grib2_convert.py |
Adds TEMPLATE_RECORD and records GRIB2_GRID_TEMPLATE; adds gaussian_grid DimCoord on reduced-gg load. |
src/iris_grib/__init__.py |
Updates save path to fall back to aux lat/lon for reduced-gg and select an ecCodes reduced-gg sample when enabled. |
src/iris_grib/_grib1_legacy/grib1_load_rules.py |
Adds special-case reference handling for surface pressure and introduces gaussian_grid DimCoord for that case. |
src/iris_grib/tests/unit/grib2_convert/test_grid_definition_template_40.py |
Updates expected metadata for GDT40 reduced load to include the gaussian_grid DimCoord. |
src/iris_grib/tests/integration/round_trip/test_grid_definition_section.py |
Converts tests to pytest style and adds an experimental GDT40 load→save→load test. |
src/iris_grib/tests/results/**/reduced*.cml |
Updates expected serialized cube outputs to include gaussian_grid. |
pyproject.toml |
Adjusts mypy configuration (disallow_untyped_decorators = false). |
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| eccodes.codes_set(grib, "longitudeOfFirstGridPoint", int(1.0e6 * lon0)) | ||
| eccodes.codes_set(grib, "longitudeOfLastGridPoint", int(1.0e6 * lon1)) | ||
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| eccodes.codes_set(grib, "N", n_lat_vals / 2) |
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| # N.B. we could here be dealing with data on a "rotated gaussion" grid, | ||
| # (GDT 3.41 or 3.43), but we don't yet support those. |
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| grib_message = eccodes.codes_grib_new_from_samples(template_name) | ||
| result = _save_rules.run(slice2D, grib_message, cube, x_coord, y_coord) | ||
| if result is not None: | ||
| grib_message = result |
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| When present, the 'GRIB_GRID_TEMPLATE' attribute is used to control how certain | ||
| types of data are saved -- notably, for gaussian grids. |
| def test_gdt40_loadsave(tmp_path, record): | ||
| loadpath = tests.get_data_path(("GRIB", "reduced", "reduced_gg.grib2")) | ||
| cube = load_cube(loadpath) | ||
| print(cube) |
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| print("\nORIGINAL:") | ||
| print(cube) | ||
| print(coord_dims_names(cube)) | ||
| print("\n\nRELOADED:") | ||
| print(cube_reloaded) |
| print(coord_dims_names(cube)) | ||
| print("\n\nRELOADED:") | ||
| print(cube_reloaded) | ||
| print(coord_dims_names(cube_reloaded)) |
| print(cube_reloaded) | ||
| print(coord_dims_names(cube_reloaded)) | ||
| assert coord_dims_names(cube_reloaded) == coord_dims_names(cube) | ||
| assert np.all(cube_reloaded.data == cube.data) |
| ReferenceTarget("ref_surface_pressure", ensure_surface_air_pressure_name) | ||
| ) | ||
| dim_coords_and_dims.append( | ||
| (DimCoord(np.arange(grib._x_points.shape[0]), long_name="gaussian_grid"), 0) |
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Addresses #785
So far, so highly sketchy + experimental
NOTE: I don't really like 94a3d38 because we only want to support calling without coords for the sake of the existing unit tests.But I tried adapting some of the existing mock-ist tests + it's really quite awkward