特定偏移Transverse Mercator投影下NaturalEarthFeature显示异常求助

问题根源 #

你犯了Cartopy使用里的典型错误：add_feature时指定的transform参数完全错了。Natural Earth的LAND、COASTLINE这类要素，默认都是基于WGS84经纬度坐标系（也就是ccrs.PlateCarree()）存储的，你却把transform设成了用来显示的Transverse Mercator投影，坐标系转换逻辑直接乱掉，才会出现全灰覆盖的异常。

修正后的代码 #

全局范围（中央经度10） #

import cartopy.crs as ccrs
import cartopy.feature as feature
import matplotlib.pyplot as plt

fig1 = plt.figure()
display_crs = ccrs.TransverseMercator(central_longitude=10)
ax = fig1.add_subplot(projection=display_crs)
ax.set_global()
# 关键：transform要用要素原始的PlateCarree坐标系
ax.add_feature(feature.LAND, transform=ccrs.PlateCarree())
ax.add_feature(feature.COASTLINE, transform=ccrs.PlateCarree())
plt.show()

北欧区域范围 #

import cartopy.crs as ccrs
import cartopy.feature as feature
import matplotlib.pyplot as plt

fig1 = plt.figure()
display_crs = ccrs.TransverseMercator(central_longitude=10)
ax = fig1.add_subplot(projection=display_crs)
ax.set_extent([2, 30, 54, 72], crs=ccrs.PlateCarree())
# 同样，transform保持PlateCarree
ax.add_feature(feature.LAND, transform=ccrs.PlateCarree())
ax.add_feature(feature.COASTLINE, transform=ccrs.PlateCarree())
plt.show()

额外：限制LAND要素绘制范围的方法 #

如果想进一步只渲染特定区域的陆地，有两种实用方法：

方法1：加载指定区域的Natural Earth子要素 #

Natural Earth提供分区域的Shapefile，比如只加载欧洲陆地：

import cartopy.crs as ccrs
import cartopy.feature as cfeature
from cartopy.io.shapereader import Reader
import matplotlib.pyplot as plt

fig, ax = plt.subplots(subplot_kw={'projection': ccrs.TransverseMercator(central_longitude=10)})
ax.set_extent([2, 30, 54, 72], crs=ccrs.PlateCarree())
# 加载本地的欧洲陆地Shapefile（需提前下载Natural Earth 1:110m尺度的陆地文件）
europe_land = cfeature.ShapelyFeature(
    Reader('ne_110m_land/ne_110m_land.shp').geometries(),
    ccrs.PlateCarree(),
    facecolor=cfeature.COLORS['land']
)
ax.add_feature(europe_land)
ax.add_feature(cfeature.COASTLINE, transform=ccrs.PlateCarree())
plt.show()

方法2：用路径裁剪全局LAND要素 #

直接对全局陆地要素做范围裁剪，不用额外下载文件：

import cartopy.crs as ccrs
import cartopy.feature as cfeature
import matplotlib.pyplot as plt
from matplotlib.path import Path

fig, ax = plt.subplots(subplot_kw={'projection': ccrs.TransverseMercator(central_longitude=10)})
extent = [2, 30, 54, 72]
ax.set_extent(extent, crs=ccrs.PlateCarree())

# 生成对应经纬度范围的裁剪路径
clip_path = Path([
    (extent[0], extent[2]),
    (extent[1], extent[2]),
    (extent[1], extent[3]),
    (extent[0], extent[3]),
    (extent[0], extent[2]),
])
# 添加陆地并应用裁剪
land_feature = ax.add_feature(cfeature.LAND, transform=ccrs.PlateCarree())
land_feature.set_clip_path(clip_path, transform=ccrs.PlateCarree())

ax.add_feature(cfeature.COASTLINE, transform=ccrs.PlateCarree())
plt.show()

内容的提问来源于stack exchange，提问作者Luis