Address review: test preserve on global templates, exact merc latitude (#3549)

Author: brendancol

xrspatial/_template_data.py

@@ -53,13 +53,13 @@
                   lonlat=(-180.0, -85.0, 180.0, 85.0), area_epsg=8857,
                   shape_epsg=3395),
     # Global Web Mercator (EPSG:3857). Native bounds are the canonical square
-    # extent +/-20037508 m, which is +/-180 lon and +/-85.051129 lat (the
+    # extent +/-20037508 m, which is +/-180 lon and +/-85.0511287798 lat (the
     # latitude where the Mercator y matches the x half-extent). lonlat stops at
-    # +/-85.051129 because Mercator y diverges to infinity at the poles.
+    # that latitude because Mercator y diverges to infinity at the poles.
     'web_mercator': dict(
         bounds=(-20037508, -20037508, 20037508, 20037508), crs=3857,
         default_resolution=50000, label='World (Web Mercator)',
-        lonlat=(-180.0, -85.051129, 180.0, 85.051129),
+        lonlat=(-180.0, -85.0511287798, 180.0, 85.0511287798),
         area_epsg=8857, shape_epsg=3395),
     # Global equal-area grid (EPSG:8857, Equal Earth). Native bounds are the
     # +/-90 world projected into Equal Earth.

xrspatial/tests/test_templates.py

@@ -578,6 +578,17 @@ def test_cf_grid_mapping_preserve_path():
     assert "Conus Albers" in agg.attrs["crs_wkt"]
 
 
+@pytest.mark.parametrize("name", ["web_mercator", "equal_earth"])
+def test_global_preserve_picks_world_projection(name):
+    # the global templates carry the same area/shape EPSG hints as 'world', so
+    # preserve='shape' lands on World Mercator (EPSG:3395) instead of a stray
+    # UTM zone for the (0, 0) centroid, and preserve='area' lands on Equal Earth
+    agg_shape = from_template(name, preserve="shape")
+    assert agg_shape.attrs["crs"] == 3395
+    assert _proj(3395) == "merc"
+    assert from_template(name, preserve="area").attrs["crs"] == 8857
+
+
 def test_grid_mapping_omitted_for_equal_earth():
     # Equal Earth (the preserve='area' fallback for the world bbox) has no
     # CF grid mapping, so grid_mapping_name is left off and crs_wkt stands