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Accept inverse_flattening = 0 for spherical ellipsoid (closes #4146) #4368

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Oct 18, 2021
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Accept inverse_flattening = 0 for spherical ellipsoid (closes #4146) #4368

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930f3bc
Accept inverse_flattening = 0 for spherical ellipsoid (closes #4146)
larsbarring Oct 12, 2021
f129e61
Added test
jamesp Oct 13, 2021
34b42ab
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Oct 13, 2021
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4 changes: 4 additions & 0 deletions docs/src/whatsnew/latest.rst
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Expand Up @@ -86,6 +86,10 @@ This document explains the changes made to Iris for this release
"Cube names differ: var1 != var1" if var1 appears multiple times in the list
(:issue:`4342`, :pull:`4345`)

#. `@larsbarring`_ fixed :class:`~iris.coord_systems.GeoCS` to handle spherical ellipsoid
parameter inverse_flattening = 0 (:issue: `4146`, :pull:`4348`)


💣 Incompatible Changes
=======================

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2 changes: 1 addition & 1 deletion lib/iris/coord_systems.py
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Expand Up @@ -196,7 +196,7 @@ def __init__(

# Perfect sphere (semi_major_axis only)? (1 0 0)
elif semi_major_axis is not None and (
semi_minor_axis is None and inverse_flattening is None
semi_minor_axis is None and not inverse_flattening
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This means that all of the following are now identical ellipsoid specifications for a sphere:

  • GeogCS(major_semi_axis=1.0, inverse_flattening=0)
  • GeogCS(major_semi_axis=1.0, inverse_flattening=None)
  • GeogCS(major_semi_axis=1.0)
  • GeogCS(1.0)

I think that this new behaviour will be quite natural to users 👍

):
semi_minor_axis = semi_major_axis
inverse_flattening = 0.0
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11 changes: 11 additions & 0 deletions lib/iris/tests/unit/coord_systems/test_GeogCS.py
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Expand Up @@ -46,6 +46,17 @@ def test_optional_args_None(self):
)
self._check_crs_defaults(crs)

def test_zero_inverse_flattening_on_perfect_sphere(self):
# allow inverse_flattening to be 0 for a perfect sphere
# i.e. semi-major axis defined, semi-minor is None.
crs = GeogCS(
1.0,
semi_minor_axis=None,
inverse_flattening=0.0,
longitude_of_prime_meridian=None,
)
self._check_crs_defaults(crs)


if __name__ == "__main__":
tests.main()