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Add explicit semi-minor axes for spherical projections #735

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ebe2b7d
Add explicit spherical projection axis
floze-the-genius Jul 18, 2026
d70af9f
Pin NumPy for Python 3.11 mypy checks
floze-the-genius Jul 18, 2026
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3 changes: 2 additions & 1 deletion .pre-commit-config.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -21,14 +21,15 @@ repos:
rev: 'v2.1.0' # Use the sha / tag you want to point at
hooks:
- id: mypy
language_version: python3.12
additional_dependencies:
- types-docutils
- types-PyYAML
- types-requests
- type_extensions
- types-setuptools
# Typed libraries
- numpy
- numpy<2.3
- pytest
args: [ --warn-unused-configs ]
- repo: https://github.com/pycqa/isort
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15 changes: 15 additions & 0 deletions pyresample/area_config.py
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Expand Up @@ -501,6 +501,7 @@ def create_area_def(area_id, projection, width=None, height=None, area_extent=No
# (hold on to EPSG code as much as possible)
if isinstance(projection, dict) and 'EPSG' in projection:
projection = "EPSG:{}".format(projection['EPSG'])
projection = _add_missing_spherical_axis(projection)

try:
crs = _get_proj_data(projection)
Expand Down Expand Up @@ -602,6 +603,20 @@ def _get_proj_data(projection: Any) -> CRS:
return CRS.from_user_input(projection)


def _add_missing_spherical_axis(projection: Any) -> Any:
"""Explicitly define a sphere when only its semi-major axis is provided."""
if not isinstance(projection, dict) or "a" not in projection:
return projection

ellipsoid_parameters = {"b", "R", "ellps", "datum", "rf", "f", "es", "e"}
if ellipsoid_parameters.intersection(projection):
return projection

projection = projection.copy()
projection["b"] = projection["a"]
return projection


def _get_proj_units(crs):
if crs.is_geographic:
unit_name = 'degrees'
Expand Down
35 changes: 35 additions & 0 deletions pyresample/test/test_area_config.py
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Expand Up @@ -312,3 +312,38 @@ def test_unused_params_warn():
units: m"""
with pytest.warns(UserWarning, match=r"Unused/unexpected area definition parameter.*revolution"):
load_area_from_string(yaml_str)


def test_projection_with_only_semi_major_axis_gets_explicit_spherical_axis():
"""Test that an incomplete spherical projection gets an explicit semi-minor axis."""
from pyresample.area_config import _add_missing_spherical_axis

projection = {"proj": "laea", "a": 6371228.0}

normalized_projection = _add_missing_spherical_axis(projection)

assert normalized_projection == {"proj": "laea", "a": 6371228.0, "b": 6371228.0}
assert projection == {"proj": "laea", "a": 6371228.0}


def test_create_area_def_passes_explicit_spherical_axis_to_geometry():
"""Test that area creation passes the completed projection to geometry construction."""
from unittest import mock

from pyresample.area_config import create_area_def

projection = {"proj": "laea", "a": 6371228.0}
with mock.patch("pyresample.area_config._make_area") as make_area:
create_area_def("test", projection)

assert make_area.call_args.args[3] == {"proj": "laea", "a": 6371228.0, "b": 6371228.0}


@pytest.mark.parametrize("ellipsoid_parameter", ["b", "R", "ellps", "datum", "rf", "f", "es", "e"])
def test_projection_with_complete_ellipsoid_is_unchanged(ellipsoid_parameter):
"""Test that existing ellipsoid definitions are preserved."""
from pyresample.area_config import _add_missing_spherical_axis

projection = {"proj": "laea", "a": 6371228.0, ellipsoid_parameter: "value"}

assert _add_missing_spherical_axis(projection) is projection
6 changes: 3 additions & 3 deletions pyresample/test/test_files/areas.cfg
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
REGION: ease_sh {
NAME: Antarctic EASE grid
PCS_ID: ease_sh
PCS_DEF: proj=laea, lat_0=-90, lon_0=0, a=6371228.0, units=m
PCS_DEF: proj=laea, lat_0=-90, lon_0=0, a=6371228.0, b=6371228.0, units=m
XSIZE: 425
YSIZE: 425
AREA_EXTENT: (-5326849.0625,-5326849.0625,5326849.0625,5326849.0625)
Expand All @@ -10,7 +10,7 @@ REGION: ease_sh {
REGION: ease_nh {
NAME: Arctic EASE grid
PCS_ID: ease_nh
PCS_DEF: proj=laea, lat_0=90, lon_0=0, a=6371228.0, units=m
PCS_DEF: proj=laea, lat_0=90, lon_0=0, a=6371228.0, b=6371228.0, units=m
XSIZE: 425
YSIZE: 425
AREA_EXTENT: (-5326849.0625,-5326849.0625,5326849.0625,5326849.0625)
Expand All @@ -19,7 +19,7 @@ REGION: ease_nh {
#REGION: commented {
# NAME: Arctic EASE grid
# PCS_ID: ease_nh
# PCS_DEF: proj=laea, lat_0=90, lon_0=0, a=6371228.0, units=m
# PCS_DEF: proj=laea, lat_0=90, lon_0=0, a=6371228.0, b=6371228.0, units=m
# XSIZE: 425
# YSIZE: 425
# AREA_EXTENT: (-5326849.0625,-5326849.0625,5326849.0625,5326849.0625)
Expand Down
13 changes: 13 additions & 0 deletions pyresample/test/test_files/areas.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ boundary:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape: [425, 425]
area_extent: [-5326849.0625, -5326849.0625, 5326849.0625, 5326849.0625]
Expand All @@ -18,6 +19,7 @@ boundary_2:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape:
height: 425
Expand All @@ -33,6 +35,7 @@ corner:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape: [425, 425]
upper_left_extent: [-5326849.0625, 5326849.0625]
Expand All @@ -47,6 +50,7 @@ corner_2:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape: [425, 425]
upper_left_extent:
Expand All @@ -64,6 +68,7 @@ circle:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
center: [0, 0]
resolution: [25067.525, 25067.525]
Expand All @@ -77,6 +82,7 @@ circle_2:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
center:
x: 0
Expand All @@ -97,6 +103,7 @@ area_of_interest:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape: [425, 425]
center: [0, 0]
Expand All @@ -110,6 +117,7 @@ area_of_interest_2:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape: [425, 425]
center:
Expand All @@ -126,6 +134,7 @@ test_meters:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape: [425, 850]
upper_left_extent:
Expand All @@ -148,6 +157,7 @@ test_degrees:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
area_extent:
lower_left_xy: [-135.0, -17.516001139327766]
Expand Down Expand Up @@ -177,6 +187,7 @@ ease_sh:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape:
height: 425
Expand All @@ -193,6 +204,7 @@ ease_nh:
lat_0: -90
lon_0: 0
a: 6371228.0
b: 6371228.0
units: m
shape:
height: 425
Expand Down Expand Up @@ -271,6 +283,7 @@ ortho:
lon_0: 40.
lat_0: -40.
a: 6370997.0
b: 6370997.0
shape:
height: 480
width: 640
Expand Down
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