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Regridding fails for geostationary coordinate systems #5485

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#5745
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Regridding fails for geostationary coordinate systems#5485
#5745
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Type: Bug
@stephenworsley

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@stephenworsley
stephenworsley
opened on Sep 8, 2023
Contributor

🐛 Bug Report

When one of the cubes involved in regridding has coordinates with a geostationary coordinate system, their units ought to be in radians, however iris insists that they ought to be in meters and regridding will fail when it gets to this line:

iris/lib/iris/analysis/_regrid.py

Lines 876 to 881 in c526ce0

if coord.units != "m":
msg = (
"Unsupported units for coordinate system. "
"Expected 'metres' got {!r}.".format(coord.units)
)
raise ValueError(msg)

This logic should be changed to allow for gesostationary coordinates with radian units.

See Proj for a description of the geostationary projection: https://proj.org/en/9.3/operations/projections/geos.html

Activity

stephenworsley
added
Type: Bug
on Sep 8, 2023
stephenworsley
self-assigned this
on Sep 8, 2023
scitools-ci
added this to 🚴 Pelotonon Sep 13, 2023
stephenworsley

stephenworsley commented on Sep 20, 2023

@stephenworsley
stephenworsley
on Sep 20, 2023
ContributorAuthor

See the CF conventions for this projection for a more concrete statement of expected units: http://cfconventions.org/cf-conventions/cf-conventions.html#_geostationary_projection

The use of projection_x_coordinate and projection_y_coordinate was deprecated in version 1.9 of the CF Conventions. The initial definition of this projection used these standard names to identify the projection coordinates even though their canonical units (meters) do not match those required for this projection (radians).

Note that this also suggests we ought to be able to handle x and y coordinates with the names projection_x_angular_coordinate and projection_y_angular_coordinate.

trexfeathers

trexfeathers commented on Oct 17, 2023

@trexfeathers
trexfeathers
on Oct 17, 2023
Contributor

In case it helps:

iris/lib/iris/plot.py

Lines 984 to 996 in e9c77c0

def _check_geostationary_coords_and_convert(x, y, kwargs):
# Geostationary stores projected coordinates as scanning angles (
# radians), in line with CF definition (this behaviour is unique to
# Geostationary). Before plotting, must be converted by multiplying by
# satellite height.
x, y = (i.copy() for i in (x, y))
transform = kwargs.get("transform")
if isinstance(transform, cartopy.crs.Geostationary):
satellite_height = transform.proj4_params["h"]
for i in (x, y):
i *= satellite_height
return x, y

trexfeathers

trexfeathers commented on Oct 26, 2023

@trexfeathers
trexfeathers
on Oct 26, 2023
Contributor

See the CF conventions for this projection for a more concrete statement of expected units: http://cfconventions.org/cf-conventions/cf-conventions.html#_geostationary_projection

The use of projection_x_coordinate and projection_y_coordinate was deprecated in version 1.9 of the CF Conventions. The initial definition of this projection used these standard names to identify the projection coordinates even though their canonical units (meters) do not match those required for this projection (radians).

Note that this also suggests we ought to be able to handle x and y coordinates with the names projection_x_angular_coordinate and projection_y_angular_coordinate.

Need to remember to update guess_coord_axis() when we add these new coordinate names.

scitools-ci
added this to 🚴 Peloton and removed this from 🚴 Pelotonon Dec 15, 2023
ESadek-MO
added this to 🐙Iris v3.8.0on Jan 31, 2024
stephenworsley
moved this to 🆕 New - potential tasks in 🐙Iris v3.8.0on Jan 31, 2024
stephenworsley
moved this from 🆕 New - potential tasks to Candidate for next sprint in 🐙Iris v3.8.0on Jan 31, 2024
stephenworsley
assigned
trexfeathers
on Jan 31, 2024
stephenworsley
moved this from Candidate for next sprint to 📋 Backlog in 🐙Iris v3.8.0on Feb 2, 2024
stephenworsley
moved this from 📋 Backlog to 🔖Assigned in 🐙Iris v3.8.0on Feb 5, 2024
stephenworsley
linked a pull request that will close this issue on Feb 14, 2024
trexfeathers
moved this from 🔖Assigned to 🏗 In progress in 🐙Iris v3.8.0on Feb 15, 2024
bjlittle
moved this from 🏗 In progress to 👀 In review in 🐙Iris v3.8.0on Feb 16, 2024
bjlittle
moved this from 👀 In review to 🏗 In progress in 🐙Iris v3.8.0on Feb 16, 2024
stephenworsley
moved this from 🏗 In progress to 👀 In review in 🐙Iris v3.8.0on Feb 16, 2024
bjlittle
assigned
bjlittle
and unassigned
trexfeathers
on Feb 16, 2024
stephenworsley
mentioned this on Feb 16, 2024
stephenworsley
moved this from 👀 In review to paused in 🐙Iris v3.8.0on Mar 12, 2024
trexfeathers
unassigned
bjlittle
and
stephenworsley
on Mar 13, 2024
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        Regridding fails for geostationary coordinate systems · Issue #5485 · SciTools/iris