Drop use of shapeOfTheEarth for Grib 1 #316
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pp-mo
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Jan 6, 2023
iris_grib/tests/results/integration/load_convert/sample_file_loads/lambert_grib1.cml
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pp-mo
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After some background reading on GRIB1, I do agree that this all makes sense.
I think it's right to say that previous behaviour was "wrong" + this is therefore a fix.
Likewise, the shift in coordinate values with projected transforms is I think just a consequence of the adjusted radius -- i.e. effectively a scaling factor, which again is a "bug fix" not "new behaviour".
So, I think all it now just needs is a whats-new entry : highlight the backwards-incompatible changes + explain it is a bug-fix.
pp-mo
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Jan 9, 2023
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Fixes #241
A more detailed summary is on that issue, in this comment but to summarise:
In eccodes v2.19.0 the default shapeOfTheEarth was changed to 0, with a radius of 6367470 m. This alligned the behaviour with GRIB2. It was also recommended to not use this key and instead use the radius key.
Previously, for backwards compatibility, we decided to circumvent this change and hardcode a value of 6 and associate this with the old radius rather than the new radius.
We have now decided to adopt the change in eccodes. This means we should also not use the shapeOfTheEarth key.
We could use the radius key instead but this assumes a spherical Earth. I think it would make more sense to use the resolutionAndComponentFlag which distinguishes between a spherical Earth and an oblate spheroidal Earth.
I have added support for a spherical Earth, but not an oblate spheroidal Earth, as this would mean adding new functionality. We could consider adding support for oblate spheroidal later should someone request it.