高纬度非矩形Cartopy投影下经纬度标签不显示问题求助

我基于Stack Overflow上的问题绘制了一幅高纬度非矩形Cartopy地图，希望在绘图的左侧/底部轴显示经纬度标签，但标签始终不显示。以下是用于生成该图的代码：

import numpy as np
import cartopy
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
from cartopy.mpl.gridliner import LONGITUDE_FORMATTER, LATITUDE_FORMATTER
import matplotlib.ticker as mticker
import cartopy.feature as cf

"""
Plot Alaska
"""

# Map View Using Cartopy
fig = plt.figure(figsize=(8,6))

xmin=-163
xmax=-120
ymin=50
ymax=71

proj = ccrs.LambertConformal(central_longitude=(xmin+xmax)/2, central_latitude=(ymin+ymax)/2)
ax = fig.add_subplot(1, 1, 1, projection=proj)
n = 20
aoi = mpath.Path(
    list(zip(np.linspace(xmin,xmax, n), np.full(n,ymax))) + \
    list(zip(np.full(n,xmax), np.linspace(ymax,ymin, n))) + \
    list(zip(np.linspace(xmax,xmin, n), np.full(n,ymin))) + \
    list(zip(np.full(n,xmin), np.linspace(ymin,ymax, n)))
)
ax.set_boundary(aoi, transform=ccrs.PlateCarree()) 

# Plot Ocean Borders
ocean = cf.NaturalEarthFeature('physical','ocean',scale='50m',edgecolor='k',facecolor='lightblue',lw=1,linestyle='-')
ax.add_feature(ocean)
# Colored Land Background
land = cf.NaturalEarthFeature('physical','land',scale='50m',facecolor='snow',lw=1,linestyle='--')
ax.add_feature(land)

ax.set_extent([xmin,xmax,ymin,ymax],crs=ccrs.PlateCarree())
ax.gridlines(draw_labels=True,crs=ccrs.PlateCarree(),x_inline=False,y_inline=False)
gl.xlocator = mticker.FixedLocator([-160,-150,-140,-130,-120])
gl.ylocator = mticker.FixedLocator([50,55,60,65,70])
gl.xformatter = LONGITUDE_FORMATTER
gl.yformatter = LATITUDE_FORMATTER

plt.show()

生成的图无经纬度轴标签：

标签不显示的核心原因是ax.gridlines()返回的Gridliner对象未正确赋值，且自定义边界后需要手动指定标签显示位置。修改步骤如下：

• 修复Gridliner变量赋值：
  原代码中ax.gridlines()直接调用但未将结果赋值给gl，导致后续配置完全无效。需修改为：

  gl = ax.gridlines(draw_labels=True,crs=ccrs.PlateCarree(),x_inline=False,y_inline=False)
  

• 明确指定标签显示位置：
  自定义边界后Cartopy无法自动识别标签位置，需手动设置显示侧并调整样式：

  # 经度标签仅显示在底部
  gl.top_labels = False
  gl.bottom_labels = True
  # 纬度标签仅显示在左侧
  gl.left_labels = True
  gl.right_labels = False
  # 调整标签字体大小避免被裁剪
  gl.xlabel_style = {'size': 10}
  gl.ylabel_style = {'size': 10}
  

• 补充遗漏的导入：
  原代码使用mpath.Path但未导入对应模块，需添加：

  import matplotlib.path as mpath
  

import numpy as np
import cartopy
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
from cartopy.mpl.gridliner import LONGITUDE_FORMATTER, LATITUDE_FORMATTER
import matplotlib.ticker as mticker
import cartopy.feature as cf
import matplotlib.path as mpath  # 补充遗漏的导入

"""
Plot Alaska
"""

# Map View Using Cartopy
fig = plt.figure(figsize=(8,6))

xmin=-163
xmax=-120
ymin=50
ymax=71

proj = ccrs.LambertConformal(central_longitude=(xmin+xmax)/2, central_latitude=(ymin+ymax)/2)
ax = fig.add_subplot(1, 1, 1, projection=proj)
n = 20
aoi = mpath.Path(
    list(zip(np.linspace(xmin,xmax, n), np.full(n,ymax))) + \
    list(zip(np.full(n,xmax), np.linspace(ymax,ymin, n))) + \
    list(zip(np.linspace(xmax,xmin, n), np.full(n,ymin))) + \
    list(zip(np.full(n,xmin), np.linspace(ymin,ymax, n)))
)
ax.set_boundary(aoi, transform=ccrs.PlateCarree()) 

# Plot Ocean Borders
ocean = cf.NaturalEarthFeature('physical','ocean',scale='50m',edgecolor='k',facecolor='lightblue',lw=1,linestyle='-')
ax.add_feature(ocean)
# Colored Land Background
land = cf.NaturalEarthFeature('physical','land',scale='50m',facecolor='snow',lw=1,linestyle='--')
ax.add_feature(land)

ax.set_extent([xmin,xmax,ymin,ymax],crs=ccrs.PlateCarree())
# 修复Gridliner赋值
gl = ax.gridlines(draw_labels=True,crs=ccrs.PlateCarree(),x_inline=False,y_inline=False)
gl.xlocator = mticker.FixedLocator([-160,-150,-140,-130,-120])
gl.ylocator = mticker.FixedLocator([50,55,60,65,70])
gl.xformatter = LONGITUDE_FORMATTER
gl.yformatter = LATITUDE_FORMATTER

# 指定标签显示位置和样式
gl.top_labels = False
gl.bottom_labels = True
gl.left_labels = True
gl.right_labels = False
gl.xlabel_style = {'size': 10}
gl.ylabel_style = {'size': 10}

plt.show()

内容的提问来源于stack exchange，提问作者kbiegseismic