Show grid ticks on geographic plots #227

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1. zxdawn commented on Sep 26, 2020

   

   zxdawn

   on Sep 26, 2020

   Author

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   This method of retrieving gridline ticks may be useful for adding the function:

   # create grid
   gridliner = ax.gridlines(draw_labels=True)
   
   # we need to draw the figure, such that the gridlines are populated
   fig.canvas.draw()   
   
   ysegs = gridliner.yline_artists[0].get_segments()
   yticks = [yseg[0,1] for yseg in ysegs]
   
   xsegs = gridliner.xline_artists[0].get_segments()
   xticks = [xseg[0,0] for xseg in xsegs]
   
   print(xticks)
   print(yticks)
   

   [-180.0, -120.0, -60.0, 0.0, 60.0, 120.0]
   [-80.0, -60.0, -40.0, -20.0, 0.0, 20.0, 40.0, 60.0, 80.0, 100.0]
   
2. lukelbd

   added

   feature

   on Jun 30, 2021
3. lukelbd commented on Jul 12, 2021

   

   lukelbd

   on Jul 12, 2021

   Collaborator

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   You can monitor #253 for updates

   Please also note the padding you see in that example is a cartopy bug confusing "pixels" with "points". It was fixed in SciTools/cartopy#1556. You can upgrade to cartopy v0.19 to get nicely-padded labels or play with ax.format(labelpad=N).
4. lukelbd

   added this to the Version 0.10 milestone on Jul 21, 2021
5. kM-Stone commented on Nov 29, 2021

   

   kM-Stone

   on Nov 29, 2021

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   Hi, maybe try ax.format(labels = False)first, then use ax.set_xticks([0, 60, 120, 180, 240, 300, 360], crs=ccrs.PlateCarree()) to specify tick lines explicitly. It worked for me with Version 0.6.4.

   import cartopy.crs as ccrs
   from cartopy.mpl.ticker import LongitudeFormatter, LatitudeFormatter
   import matplotlib.pyplot as plt
   import proplot as pplt
   
   # plt.figure(figsize=(8, 10))
   fig, ax1 = pplt.subplots(proj=ccrs.PlateCarree(central_longitude=180),width=5)
   
   ax1.coastlines()
   
   lon_formatter = LongitudeFormatter(zero_direction_label=True)
   lat_formatter = LatitudeFormatter()
   ax1.xaxis.set_major_formatter(lon_formatter)
   ax1.yaxis.set_major_formatter(lat_formatter)
   
   ax1.set_xticks([30, 60, 120, 180, 240, 300, 350], crs=ccrs.PlateCarree())
   ax1.set_yticks([0, 20, 40], crs=ccrs.PlateCarree())
   
   ax1.tick_params(which='minor',direction='out',length=3,width=1,)
   ax1.tick_params(which='major',direction='out', length=5, width=1, colors='k',)
   
   ax1.format(land=True,
           #    labels=True,
              gridminor=True,
              lonlim=(-140, 60),
              latlim=(-10, 50))
   

   

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6. syrte commented on Jan 14, 2022

   

   syrte

   on Jan 14, 2022

   Last edited by syrte

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   kM-Stone's solution does not work properly for some other projections such as 'gnom'.

   ---> 16 ax1.set_xticks([30, 60, 120, 180, 240, 300, 350], crs=ccrs.PlateCarree())
        17 ax1.set_yticks([0, 20, 40], crs=ccrs.PlateCarree())
        18 
   
   ~/local/conda/envs/myenv/lib/python3.8/site-packages/cartopy/mpl/geoaxes.py in set_xticks(self, ticks, minor, crs)
       986                                    (ccrs._RectangularProjection,
       987                                     ccrs.Mercator)):
   --> 988                 raise RuntimeError('Cannot handle non-rectangular coordinate '
       989                                    'systems.')
       990             proj_xyz = self.projection.transform_points(crs,
   
   RuntimeError: Cannot handle non-rectangular coordinate systems.
   

   I found a temporary workaround for general projections. I put it here in case it is helpful for anyone.

   import numpy as np
   import proplot as pplt
   
   
   def add_ticks(ax, labelpad=None):
       """Only works for major ticks on the left and bottom."""
       ax.grid(False)
       ax.tick_params('both', which='major', size=pplt.rc['tick.len'])
       if labelpad is None:
           labelpad = pplt.rc['tick.len'] + 2
   
       for gl in ax._gridliners:
           gl.xpadding = gl.ypadding = labelpad
       ax.format(labelpad=labelpad)
       ax.figure.canvas.draw_idle()  # necessary for generating xlabel_artists...
   
       for gl in ax._gridliners:
           xy = np.array([t.get_position() for t in gl.bottom_label_artists if t.get_visible()])
           if xy.any():
               ax.set_xticks(xy[:, 0])
               ax.set_xticklabels([])
   
           xy = np.array([t.get_position() for t in gl.left_label_artists if t.get_visible()])
           if xy.any():
               ax.set_yticks(xy[:, 1])
               ax.set_yticklabels([])
   
   
   fig = pplt.figure(span=False, suptitle='Example')
   ax = fig.subplot(111, proj='gnom', proj_kw={'lon_0': 0, 'lat_0': 45})
   ax.format(lonlim=(-20, 20), latlim=(30, 60),
             labels=True, grid=True, gridminor=True,
             lonlocator=np.arange(-50, 50, 5), latlocator=5,
             )
   add_ticks(ax)

   

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7. lukelbd

   modified the milestones: Version 0.10, Version 0.11 on Jan 25, 2022