Full-featured Mercator coord system #3041
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@@ -831,7 +831,9 @@ class Mercator(CoordSystem): | |
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| grid_mapping_name = "mercator" | ||
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| def __init__(self, longitude_of_projection_origin=0.0, ellipsoid=None, | ||
| min_latitude=-80.0, max_latitude=84.0, | ||
| true_scale_lat=0.0): | ||
| """ | ||
| Constructs a Mercator coord system. | ||
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@@ -840,17 +842,33 @@ def __init__(self, longitude_of_projection_origin=0, ellipsoid=None): | |
| True longitude of planar origin in degrees. | ||
| * ellipsoid | ||
| :class:`GeogCS` defining the ellipsoid. | ||
| * min_latitude | ||
| the maximum southerly extent of the projection. | ||
| Defaults to -80 degrees. | ||
| * max_latitude | ||
| the maximum northerly extent of the projection. | ||
| Defaults to 84 degrees. | ||
| * true_scale_lat | ||
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There was a problem hiding this comment. Is this the name used by CF? Could you reference these in your description to speed up xreferencing please? There was a problem hiding this comment. Looks like CF accepts one of two names: http://cfconventions.org/cf-conventions/cf-conventions.html#_mercator. I'm going to go with |
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| the latitude where the scale is 1. Defaults to 0 degrees. | ||
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| """ | ||
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There was a problem hiding this comment. I agree that these aren't particularly well written, but I don't want to lose the docstrings altogether. There was a problem hiding this comment. Sorry! I always forget about these special comments (perhaps because it's so unclear that they do even have special behaviour). In fact, I thought they were just unnecessary duplications of the docstring above... I'll reinstate them and add another for the new kwarg I've introduced. |
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| self.longitude_of_projection_origin = longitude_of_projection_origin | ||
| self.ellipsoid = ellipsoid | ||
| self.min_latitude = min_latitude | ||
| self.max_latitude = max_latitude | ||
| self.true_scale_lat = true_scale_lat | ||
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| def __repr__(self): | ||
| res = ("Mercator(longitude_of_projection_origin={!r}, " | ||
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There was a problem hiding this comment. I'm completely happy with your implementation. FWIW, if I was implementing this though, I'd have done:
There was a problem hiding this comment. Yeah, it was line length that put me off doing that... There was a problem hiding this comment. Also, I think that's actually less readable than having unnamed args in the format string. There was a problem hiding this comment.
That horse has bolted I'm afraid... https://www.python.org/dev/peps/pep-0498/ There was a problem hiding this comment.
Yes yes I know, and it makes full sense in the case of full format strings (i.e. |
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| "ellipsoid={!r}, " | ||
| "min_latitude={!r}, " | ||
| "max_latitude={!r}, " | ||
| "true_scale_lat={!r})") | ||
| return res.format(self.longitude_of_projection_origin, | ||
| self.ellipsoid, | ||
| self.min_latitude, | ||
| self.max_latitude, | ||
| self.true_scale_lat) | ||
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| def as_cartopy_crs(self): | ||
| if self.ellipsoid is not None: | ||
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@@ -860,7 +878,10 @@ def as_cartopy_crs(self): | |
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| return ccrs.Mercator( | ||
| central_longitude=self.longitude_of_projection_origin, | ||
| globe=globe, | ||
| min_latitude=self.min_latitude, | ||
| max_latitude=self.max_latitude, | ||
| latitude_true_scale=self.true_scale_lat) | ||
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| def as_cartopy_projection(self): | ||
| return self.as_cartopy_crs() | ||
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| @@ -1,2 +1,2 @@ | ||
| <?xml version="1.0" ?> | ||
| <mercator ellipsoid="GeogCS(semi_major_axis=6377563.396, semi_minor_axis=6356256.909)" longitude_of_projection_origin="90.0" max_latitude="84.0" min_latitude="-80.0" true_scale_lat="0.0"/> |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,116 @@ | ||
| # (C) British Crown Copyright 2018, Met Office | ||
| # | ||
| # This file is part of Iris. | ||
| # | ||
| # Iris is free software: you can redistribute it and/or modify it under | ||
| # the terms of the GNU Lesser General Public License as published by the | ||
| # Free Software Foundation, either version 3 of the License, or | ||
| # (at your option) any later version. | ||
| # | ||
| # Iris is distributed in the hope that it will be useful, | ||
| # but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| # GNU Lesser General Public License for more details. | ||
| # | ||
| # You should have received a copy of the GNU Lesser General Public License | ||
| # along with Iris. If not, see <http://www.gnu.org/licenses/>. | ||
| """Unit tests for the :class:`iris.coord_systems.Mercator` class.""" | ||
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| from __future__ import (absolute_import, division, print_function) | ||
| from six.moves import (filter, input, map, range, zip) # noqa | ||
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| # Import iris.tests first so that some things can be initialised before | ||
| # importing anything else. | ||
| import iris.tests as tests | ||
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| import cartopy.crs as ccrs | ||
| from iris.coord_systems import GeogCS, Mercator | ||
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| class Test_Mercator__basics(tests.IrisTest): | ||
| def setUp(self): | ||
| self.tm = Mercator(longitude_of_projection_origin=90.0, | ||
| ellipsoid=GeogCS(6377563.396, 6356256.909)) | ||
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| def test_construction(self): | ||
| self.assertXMLElement(self.tm, ("coord_systems", "Mercator.xml")) | ||
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| def test_repr(self): | ||
| expected = ("Mercator(longitude_of_projection_origin=90.0, " | ||
| "ellipsoid=GeogCS(semi_major_axis=6377563.396, " | ||
| "semi_minor_axis=6356256.909), " | ||
| "min_latitude=-80.0, max_latitude=84.0, " | ||
| "true_scale_lat=0.0)") | ||
| self.assertEqual(expected, repr(self.tm)) | ||
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| class Test_Mercator__as_cartopy_crs(tests.IrisTest): | ||
| def test_simple(self): | ||
| # Check that a projection set up with all the defaults is correctly | ||
| # converted to a cartopy CRS. | ||
| merc_cs = Mercator() | ||
| res = merc_cs.as_cartopy_crs() | ||
| expected = ccrs.Mercator(globe=ccrs.Globe()) | ||
| self.assertEqual(res, expected) | ||
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| def test_extra_kwargs(self): | ||
| # Check that a projection with non-default values is correctly | ||
| # converted to a cartopy CRS. | ||
| longitude_of_projection_origin = 90.0 | ||
| min_lat = -75.0 | ||
| true_scale_lat = 14.0 | ||
| ellipsoid = GeogCS(semi_major_axis=6377563.396, | ||
| semi_minor_axis=6356256.909) | ||
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| merc_cs = Mercator( | ||
| longitude_of_projection_origin, | ||
| ellipsoid=ellipsoid, | ||
| min_latitude=min_lat, | ||
| true_scale_lat=true_scale_lat) | ||
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| expected = ccrs.Mercator( | ||
| central_longitude=longitude_of_projection_origin, | ||
| globe=ccrs.Globe(semimajor_axis=6377563.396, | ||
| semiminor_axis=6356256.909, ellipse=None), | ||
| min_latitude=min_lat, | ||
| latitude_true_scale=true_scale_lat) | ||
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| res = merc_cs.as_cartopy_crs() | ||
| self.assertEqual(res, expected) | ||
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| class Test_as_cartopy_projection(tests.IrisTest): | ||
| def test_simple(self): | ||
| # Check that a projection set up with all the defaults is correctly | ||
| # converted to a cartopy projection. | ||
| merc_cs = Mercator() | ||
| res = merc_cs.as_cartopy_projection() | ||
| expected = ccrs.Mercator(globe=ccrs.Globe()) | ||
| self.assertEqual(res, expected) | ||
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| def test_extra_kwargs(self): | ||
| longitude_of_projection_origin = 90.0 | ||
| max_lat = 80.0 | ||
| true_scale_lat = 14.0 | ||
| ellipsoid = GeogCS(semi_major_axis=6377563.396, | ||
| semi_minor_axis=6356256.909) | ||
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| merc_cs = Mercator( | ||
| longitude_of_projection_origin, | ||
| ellipsoid=ellipsoid, | ||
| max_latitude=max_lat, | ||
| true_scale_lat=true_scale_lat) | ||
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| expected = ccrs.Mercator( | ||
| central_longitude=longitude_of_projection_origin, | ||
| globe=ccrs.Globe(semimajor_axis=6377563.396, | ||
| semiminor_axis=6356256.909, ellipse=None), | ||
| max_latitude=max_lat, | ||
| latitude_true_scale=true_scale_lat) | ||
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| res = merc_cs.as_cartopy_projection() | ||
| self.assertEqual(res, expected) | ||
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| if __name__ == "__main__": | ||
| tests.main() |
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Where do these come from? If cartopy, I'd discourage default at all for these kwargs - they aren't fundamental parts of the reference system AFAIKS.
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Actually, GRIB GDT10 doesn't define min/max latitude, so we could drop these again (we only really need the true scale latitude). Otherwise yes, these come from cartopy.