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Gridline for Lambert Projection #935

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ShihengDuan opened this issue Jun 16, 2023 · 1 comment · Fixed by #954
Closed

Gridline for Lambert Projection #935

ShihengDuan opened this issue Jun 16, 2023 · 1 comment · Fixed by #954
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@lee1043
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@ShihengDuan
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Hi,

I noticed the gridline is disabled for Lambert projections across 180 longitude line

pcmdi_metrics/pcmdi_metrics/variability_mode/lib/plot_map.py

Lines 49 to 50 in 4561314

if mode in ["PNA", "PDO", "NPGO", "AMO"] and projection == "Lambert":
gridline = False
.
A figure from a previous version of PMP (cannot remember the version number):
image
It seems the gridline is conflict with ax.boundary, that the longitude does not go beyond 180 degree.

max_lat = 70
min_lon = 110
max_lon = 260
max_lat = min(max_lat, 80)  
min_lat = 20
central_longitude = (min_lon + max_lon) / 2.0
central_latitude = (min_lat + max_lat) / 2.0
print(central_longitude)
projection = cartopy.crs.AlbersEqualArea(
            central_longitude=central_longitude,
            central_latitude=central_latitude,
            standard_parallels=(20, max_lat),
        )

vertices = [
            (lon, min_lat) for lon in range(int(min_lon), int(max_lon + 1), 1)
        ] + [(lon, max_lat) for lon in range(int(max_lon), int(min_lon - 1), -1)]

boundary = mpath.Path(vertices)
fig, ax = plt.subplots(nrows=1, ncols=1, subplot_kw={'projection':projection}, figsize=(8, 5))
ax.add_feature(cartopy.feature.COASTLINE)
ax.set_boundary(boundary, transform=cartopy.crs.PlateCarree())
ax.set_extent([min_lon, max_lon, min_lat, max_lat], crs=cartopy.crs.PlateCarree())
gl = ax.gridlines(draw_labels=True, alpha=0.8, linestyle="--", crs=cartopy.crs.PlateCarree())
gl.xformatter = LONGITUDE_FORMATTER 
gl.yformatter = LATITUDE_FORMATTER
gl.ylocator = mticker.FixedLocator([30, 60])
gl.xlocator = mticker.FixedLocator([120, 160, 200-360, 240-360])
gl.top_labels = False
plt.show()

Figure:
image

A possible workaround is here

max_lat = 70
min_lon = 110
max_lon = 260
max_lat = min(max_lat, 80)  
min_lat = 20
central_longitude = (min_lon + max_lon) / 2.0
central_latitude = (min_lat + max_lat) / 2.0
print(central_longitude)
projection = cartopy.crs.AlbersEqualArea(
            central_longitude=central_longitude,
            central_latitude=central_latitude,
            standard_parallels=(20, max_lat),
        )

vertices = [
            (lon-180, min_lat) for lon in range(int(min_lon), int(max_lon + 1), 1)
        ] + [(lon-180, max_lat) for lon in range(int(max_lon), int(min_lon - 1), -1)]

boundary = mpath.Path(vertices)
fig, ax = plt.subplots(nrows=1, ncols=1, subplot_kw={'projection':projection}, figsize=(8, 5))
ax.add_feature(cartopy.feature.COASTLINE)
ax.set_boundary(boundary, transform=cartopy.crs.PlateCarree(central_longitude=180))
ax.set_extent([min_lon, max_lon, min_lat, max_lat], crs=cartopy.crs.PlateCarree())
gl = ax.gridlines(draw_labels=True, alpha=0.8, linestyle="--", crs=cartopy.crs.PlateCarree())
gl.xformatter = LONGITUDE_FORMATTER 
gl.yformatter = LATITUDE_FORMATTER
gl.ylocator = mticker.FixedLocator([30, 60])
gl.xlocator = mticker.FixedLocator([120, 160, 200-360, 240-360])
gl.top_labels = False
plt.draw()
for ea in gl.ylabel_artists:
    right_label = ea.get_position()[0] > 0
    # print(ea, ea.get_position()[0], ea.get_visible())
    if right_label:
        ea.set_visible(False)
plt.show()

Figure:
image
Reference issue: SciTools/cartopy#2173 (comment)
@lee1043
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lee1043 commented Jun 20, 2023

@ShihengDuan Thank you for posting this! I will fix it with the workaround!

@lee1043 lee1043 self-assigned this Jun 29, 2023
@lee1043 lee1043 added the bug label Jun 29, 2023
@lee1043 lee1043 linked a pull request Jun 29, 2023 that will close this issue
Lambert map projection plots #954
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Lambert map projection plots PCMDI/pcmdi_metrics
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@lee1043 @ShihengDuan