This is a fix for cartopy `ax.gridlines()` that allows adding labels even for non-rectangular projections

gridlines_with_labels.py

import numpy as np
import cartopy
import cartopy.crs as ccrs
from cartopy.mpl.gridliner import LONGITUDE_FORMATTER, LATITUDE_FORMATTER


def gridlines_with_labels(ax, top=True, bottom=True, left=True,
                          right=True, **kwargs):
    """
    Like :meth:`cartopy.mpl.geoaxes.GeoAxes.gridlines`, but will draw
    gridline labels for arbitrary projections.

    Parameters
    ----------
    ax : :class:`cartopy.mpl.geoaxes.GeoAxes`
        The :class:`GeoAxes` object to which to add the gridlines.
    top, bottom, left, right : bool, optional
        Whether or not to add gridline labels at the corresponding side
        of the plot (default: all True).
    kwargs : dict, optional
        Extra keyword arguments to be passed to :meth:`ax.gridlines`.

    Returns
    -------
    :class:`cartopy.mpl.gridliner.Gridliner`
        The :class:`Gridliner` object resulting from ``ax.gridlines()``.

    Example
    -------
    >>> import matplotlib.pyplot as plt
    >>> import cartopy.crs as ccrs
    >>> plt.figure(figsize=(10, 10))
    >>> ax = plt.axes(projection=ccrs.Orthographic(-5, 53))
    >>> ax.set_extent([-10.0, 0.0, 50.0, 56.0], crs=ccrs.PlateCarree())
    >>> ax.coastlines('10m')
    >>> gridlines_with_labels(ax)
    >>> plt.show()

    """

    # Add gridlines
    gridliner = ax.gridlines(**kwargs)

    ax.tick_params(length=0)

    # Get projected extent
    xmin, xmax, ymin, ymax = ax.get_extent()

    # Determine tick positions
    sides = {}
    N = 500
    if bottom:
        sides['bottom'] = np.stack([np.linspace(xmin, xmax, N),
                                    np.ones(N) * ymin])
    if top:
        sides['top'] = np.stack([np.linspace(xmin, xmax, N),
                                np.ones(N) * ymax])
    if left:
        sides['left'] = np.stack([np.ones(N) * xmin,
                                  np.linspace(ymin, ymax, N)])
    if right:
        sides['right'] = np.stack([np.ones(N) * xmax,
                                   np.linspace(ymin, ymax, N)])

    # Get latitude and longitude coordinates of axes boundary at each side
    # in discrete steps
    gridline_coords = {}
    for side, values in sides.items():
        gridline_coords[side] = ccrs.PlateCarree().transform_points(
            ax.projection, values[0], values[1])

    lon_lim, lat_lim = gridliner._axes_domain(
        background_patch=ax.background_patch)
    ticklocs = {
        'x': gridliner.xlocator.tick_values(lon_lim[0], lon_lim[1]),
        'y': gridliner.ylocator.tick_values(lat_lim[0], lat_lim[1])
    }

    # Compute the positions on the outer boundary where
    coords = {}
    for name, g in gridline_coords.items():
        if name in ('bottom', 'top'):
            compare, axis = 'x', 0
        else:
            compare, axis = 'y', 1
        coords[name] = np.array([
            sides[name][:, np.argmin(np.abs(
                gridline_coords[name][:, axis] - c))]
            for c in ticklocs[compare]
        ])

    # Create overlay axes for top and right tick labels
    ax_topright = ax.figure.add_axes(ax.get_position(), frameon=False)
    ax_topright.tick_params(
        left=False, labelleft=False,
        right=True, labelright=True,
        bottom=False, labelbottom=False,
        top=True, labeltop=True,
        length=0
    )
    ax_topright.set_xlim(ax.get_xlim())
    ax_topright.set_ylim(ax.get_ylim())

    for side, tick_coords in coords.items():
        if side in ('bottom', 'top'):
            axis, idx = 'x', 0
        else:
            axis, idx = 'y', 1

        _ax = ax if side in ('bottom', 'left') else ax_topright

        ticks = tick_coords[:, idx]

        valid = np.logical_and(
            ticklocs[axis] >= gridline_coords[side][0, idx],
            ticklocs[axis] <= gridline_coords[side][-1, idx])

        if side in ('bottom', 'top'):
            _ax.set_xticks(ticks[valid])
            _ax.set_xticklabels([LONGITUDE_FORMATTER.format_data(t)
                                 for t in ticklocs[axis][valid]])
        else:
            _ax.set_yticks(ticks[valid])
            _ax.set_yticklabels([LATITUDE_FORMATTER.format_data(t)
                                 for t in ticklocs[axis][valid]])

    return gridliner

sample_map.pdf

Thanks for the solution. However, i get this issue:
TypeError: _axes_domain() got an unexpected keyword argument 'background_patch'

Thanks for the solution. However, i get this issue:
TypeError: _axes_domain() got an unexpected keyword argument 'background_patch'

@vinodkatmos I believe this workaround is now obsolete as Cartopy supports gridline labels for non-rectangular projections natively as of version 0.18.

I had to modify this is make it work for me (python 3.8, matplotlib 3.3.1, cartopy 0.18)

`import numpy as np
import cartopy.crs as ccrs
from cartopy.mpl.gridliner import LONGITUDE_FORMATTER, LATITUDE_FORMATTER

def gridlines_with_labels(ax, top=True, bottom=True, left=True,
right=True, **kwargs):
"""
Parameters
----------
ax : :class:cartopy.mpl.geoaxes.GeoAxes
The :class:GeoAxes object to which to add the gridlines.
top, bottom, left, right : bool, optional
Whether or not to add gridline labels at the corresponding side
of the plot (default: all True).
kwargs : dict, optional
Extra keyword arguments to be passed to :meth:ax.gridlines.
Returns
-------
:class:cartopy.mpl.gridliner.Gridliner
The :class:Gridliner object resulting from ax.gridlines().
Example
-------
>>> import matplotlib.pyplot as plt
>>> import cartopy.crs as ccrs
>>> plt.figure(figsize=(10, 10))
>>> ax = plt.axes(projection=ccrs.Orthographic(-5, 53))
>>> ax.set_extent([-10.0, 0.0, 50.0, 56.0], crs=ccrs.PlateCarree())
>>> ax.coastlines('10m')
>>> gridlines_with_labels(ax)
>>> plt.show()
"""

# Add gridlines
gridliner = ax.gridlines(**kwargs)

ax.tick_params(length=0)

# Get projected extent
xmin, xmax, ymin, ymax = ax.get_extent()

# Determine tick positions
sides = {}
N = 500
if bottom:
    sides['bottom'] = np.stack([np.linspace(xmin, xmax, N),
                                np.ones(N) * ymin])
if top:
    sides['top'] = np.stack([np.linspace(xmin, xmax, N),
                            np.ones(N) * ymax])
if left:
    sides['left'] = np.stack([np.ones(N) * xmin,
                              np.linspace(ymin, ymax, N)])
if right:
    sides['right'] = np.stack([np.ones(N) * xmax,
                               np.linspace(ymin, ymax, N)])

# Get latitude and longitude coordinates of axes boundary at each side
# in discrete steps
gridline_coords = {}
for side, values in sides.items():
    gridline_coords[side] = ccrs.PlateCarree().transform_points(
        ax.projection, values[0], values[1])

lon_lim, lat_lim = gridliner._axes_domain()
ticklocs = {
    'x': gridliner.xlocator.tick_values(lon_lim[0], lon_lim[1]),
    'y': gridliner.ylocator.tick_values(lat_lim[0], lat_lim[1])
}

# Compute the positions on the outer boundary where
coords = {}
for name, g in gridline_coords.items():
    if name in ('bottom', 'top'):
        compare, axis = 'x', 0
    else:
        compare, axis = 'y', 1
    coords[name] = np.array([
        sides[name][:, np.argmin(np.abs(
            gridline_coords[name][:, axis] - c))]
        for c in ticklocs[compare]
    ])

# Create overlay axes for top and right tick labels
ax_topright = ax.figure.add_axes(ax.get_position(), frameon=False)
ax_topright.tick_params(
    left=False, labelleft=False,
    right=right, labelright=right,
    bottom=False, labelbottom=False,
    top=top, labeltop=top,
    length=0
)
ax_topright.set_xlim(ax.get_xlim())
ax_topright.set_ylim(ax.get_ylim())

for side, tick_coords in coords.items():
    if side in ('bottom', 'top'):
        axis, idx = 'x', 0
    else:
        axis, idx = 'y', 1

    _ax = ax if side in ('bottom', 'left') else ax_topright

    ticks = tick_coords[:, idx]

    valid = np.logical_and(
        ticklocs[axis] >= gridline_coords[side][0, idx],
        ticklocs[axis] <= gridline_coords[side][-1, idx])

    if side in ('bottom', 'top'):
        _ax.set_xticks(ticks[valid])
        _ax.set_xticklabels([LONGITUDE_FORMATTER.format_data(t)
                             for t in ticklocs[axis][valid]])
    else:
        _ax.set_yticks(ticks[valid])
        _ax.set_yticklabels([LATITUDE_FORMATTER.format_data(t)
                             for t in np.asarray(ticklocs[axis])[valid]])

return gridliner`

@vinodkatmos For Cartopy 0.18, just use the built-in ax.gridlines(draw_labels=True) instead of this workaround.

@jnhansen Thanks a lot. The only thing i had to make sure is to specify crs=ccrs.PlateCarree() in ax.set_extent and remove crs=ccrs.Orthographic() in ax.gridlines(draw_labels=True).