缩放 cartopy plot 时更新纬度/经度轴

Question

I am plotting some data in cartopy. I would like to be able to zoom in on a region of the map and have the latitude/longitude axes update to reflect the zoomed in region. Instead, they just dissapear altogether when I zoom in. How do I fix this?

Here is my code for generating the axes

plt.figure()
ax = plt.axes(projection=cartopy.crs.PlateCarree())
ax.add_feature(cartopy.feature.LAND, edgecolor='black')
gl = ax.gridlines(crs=cartopy.crs.PlateCarree(), draw_labels=True,
                  linewidth=2, color='gray', alpha=0.5, linestyle='--')
# plot some stuff here

Answer 1

It is possible to update the cartopy gridliners in interactive mode, but you need to subclass the Navigation toolbar.

In this example below I have used a PySide/QT5 example code that allows me to substitute a subclassed toolbar, then merged in the gridliner example code. The overloaded toolbar callbacks recreate the gridlines everytime zoom/pan/home is used.

I used python3.8, matplotlib-3.4.2, cartopy-0.20

import sys
from PySide2 import QtWidgets
from PySide2.QtWidgets import QVBoxLayout

from matplotlib.figure import Figure
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar
import cartopy.crs as ccrs


class CustomNavigationToolbar(NavigationToolbar):
    toolitems = [t for t in NavigationToolbar.toolitems if t[0] in ('Home', 'Pan', 'Zoom', 'Save')]

    def __init__(self, canvas, parent, coordinates=True, func_recreate_gridlines=None):
        print('CustomNavigationToolbar::__init__')
        super(CustomNavigationToolbar, self).__init__(canvas, parent, coordinates)
        self.func_recreate_gridlines = func_recreate_gridlines

    def home(self, *args):
        print('CustomNavigationToolbar::home')
        super(CustomNavigationToolbar, self).home(*args)
        if self.func_recreate_gridlines is not None:
            self.func_recreate_gridlines()

    def release_pan(self, event):
        print('CustomNavigationToolbar::release_pan')
        super(CustomNavigationToolbar, self).release_pan(event)
        if self.func_recreate_gridlines is not None:
            self.func_recreate_gridlines()

    def release_zoom(self, event):
        print('CustomNavigationToolbar::release_zoom')
        super(CustomNavigationToolbar, self).release_zoom(event)
        if self.func_recreate_gridlines is not None:
            self.func_recreate_gridlines()


class ApplicationWindow(QtWidgets.QMainWindow):
    def __init__(self):
        print('ApplicationWindow::__init__')
        super().__init__()

        self._main = QtWidgets.QWidget()
        self.setCentralWidget(self._main)
        self.layout = QVBoxLayout(self._main)

        self.fig = Figure()
        self.canvas = FigureCanvas(self.fig)
        self.toolbar = CustomNavigationToolbar(self.canvas, self,
                                               coordinates=True,
                                               func_recreate_gridlines=self.recreate_gridlines)
        self.layout.addWidget(self.canvas)
        self.addToolBar(self.toolbar)

        # figure setup taken from gridlines example at
        # https://scitools.org.uk/cartopy/docs/latest/matplotlib/gridliner.html
        projection = ccrs.RotatedPole(pole_longitude=120.0, pole_latitude=70.0)
        self.ax = self.canvas.figure.add_subplot(1, 1, 1, projection=projection)
        self.ax.set_extent([-6, 3, 48, 58], crs=ccrs.PlateCarree())
        self.ax.coastlines(resolution='10m')

        self._gl = None
        self.recreate_gridlines()

    def recreate_gridlines(self):
        print('ApplicationWindow::recreate_gridlines')

        print(' remove old gridliner artists')
        if self._gl is not None:
            for artist_coll in [self._gl.xline_artists, self._gl.yline_artists, self._gl.xlabel_artists, self._gl.ylabel_artists]:
                for a in artist_coll:
                    a.remove()
            self.ax._gridliners = []

        print(' self.ax.gridlines()')
        self._gl = self.ax.gridlines(crs=ccrs.PlateCarree(),
                                     draw_labels=True, dms=True, x_inline=False, y_inline=False)


if __name__ == "__main__":
    qapp = QtWidgets.QApplication(sys.argv)
    app = ApplicationWindow()
    app.show()
    qapp.exec_()