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Add latitude_true_scale to ccrs.LambertCylindrical #2588

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Add latitude_true_scale to ccrs.LambertCylindrical #2588

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12 changes: 10 additions & 2 deletions lib/cartopy/crs.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1730,12 +1730,20 @@ def y_limits(self):


class LambertCylindrical(_RectangularProjection):
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@greglucas greglucas Oct 30, 2025

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Should we actually create a different class GallPeters with a fixed lat_ts=45 and/or a CylindricalEqualArea superclass that takes the new keyword argument. It looks like the Lambert version is specifically for lat_ts=0
https://proj.org/en/stable/operations/projections/cea.html

def __init__(self, central_longitude=0.0, globe=None):
def __init__(self, central_longitude=0.0, globe=None,
latitude_true_scale=0.0):
globe = globe or Globe(semimajor_axis=WGS84_SEMIMAJOR_AXIS)
proj4_params = [('proj', 'cea'), ('lon_0', central_longitude),
('lat_ts', latitude_true_scale),
('to_meter', math.radians(1) * (
globe.semimajor_axis or WGS84_SEMIMAJOR_AXIS))]
super().__init__(proj4_params, 180, math.degrees(1), globe=globe)
stretch_factor = np.cos(np.deg2rad(latitude_true_scale)) ** 2
super().__init__(
proj4_params,
180 * np.sqrt(stretch_factor),
math.degrees(1) / np.sqrt(stretch_factor),
globe=globe,
)


class LambertConformal(Projection):
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3 changes: 3 additions & 0 deletions lib/cartopy/tests/mpl/test_gridliner.py
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,9 @@
ccrs.AzimuthalEquidistant,
ccrs.LambertConformal,
ccrs.LambertCylindrical,
pytest.param((ccrs.LambertCylindrical, dict(latitude_true_scale=45)),
id='GallPeters'),
ccrs.LambertCylindrical,
ccrs.Mercator,
ccrs.Miller,
ccrs.Mollweide,
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