Cartopy 无法在旋转网格上正确绘制轮廓数据

Question

当绘制在旋转极网格上定义的数据集的轮廓时，我得到以下结果：

这只是在使用 contour 和 contourf 时出现的问题，而不是 pcolormesh。

有人知道这里会发生什么吗？我应该提交错误报告吗？如果是，我应该使用 cartopy 还是使用 matplotlib？

复制

示例笔记本 https://github.com/lvankampenhout/Whosebug-rotatedpole/blob/master/Minimum%20example.ipynb
示例数据http://www.staff.science.uu.nl/~kampe004/files/snow_rlat_rlon.nc

Answer 1

等高线数据应分为两部分以避免您发现错误。我选择 longitude=0 作为分割线。 Numpy 的掩码数组技术用于实现数据操作。这是生成有用图的工作代码。

import numpy as np
import cartopy.crs as ccrs
import matplotlib as mpl
import matplotlib.colors as colors
import matplotlib.pyplot as plt
import numpy.ma as ma
from netCDF4 import Dataset

nc = Dataset('./data/snow_rlat_rlon.nc')

# Prep values for contouring
snow_2d_array = nc.variables[u'snowfall'][:]   # need *(86400*365); mm/s-> mm/yr
lat_2d_array = nc.variables[u'lat2d'][:]
lon_2d_array = nc.variables[u'lon2d'][:]

# do masked-array on the lon_2d
lon2d_greater = ma.masked_greater(lon_2d_array, -0.01)
lon2d_lesser = ma.masked_less(lon_2d_array, 0)

# apply masks to other associate arrays: lat_2d
lat2d_greater = ma.MaskedArray(lat_2d_array, mask=lon2d_greater.mask)
lat2d_lesser = ma.MaskedArray(lat_2d_array, mask=lon2d_lesser.mask)
# apply masks to other associate arrays: snow_2d
snow_2d_greater = ma.MaskedArray(snow_2d_array, mask=lon2d_greater.mask)
snow_2d_lesser = ma.MaskedArray(snow_2d_array, mask=lon2d_lesser.mask)

# set levels for contouring of snow_2d
levels = (0, 25, 50, 75, 100, 200, 400, 600, 800, 1000, 2000, 4000)

# get snow_2d value-limits for use with colormap
vmax, vmin = snow_2d_array.max()*86400*365, snow_2d_array.min()*86400*365
cmap1 = "viridis"
norm1 = colors.BoundaryNorm(boundaries=levels, ncolors=16)
norm2 = colors.Normalize(vmin=vmin, vmax=vmax/4)

# setup fig+axes, specifying projection to use
fig, ax = plt.subplots(subplot_kw={'projection': ccrs.SouthPolarStereo()})
fig.set_size_inches([10, 10])

ax.coastlines(color="red", linewidth=2)  # draw coastlines in red

# plot contour using each part of the 2 masked data sets
ct1 = ax.contour(lon2d_greater, lat2d_greater, snow_2d_greater*86400*365, \
                 norm=norm2, levels=levels, \
                 transform=ccrs.PlateCarree())

ct2 = ax.contour(lon2d_lesser, lat2d_lesser, snow_2d_lesser*86400*365, \
                 norm=norm2, levels=levels, \
                 transform=ccrs.PlateCarree()) 

#plt.colorbar(ct1, shrink=0.85)
plt.show()

输出图：

对于填充轮廓，将 ax.contour() 替换为 ax.contourf() 并添加：

ax.set_xlim((-4052327.4304452268, 4024164.250636036))

在plt.show()前。

希望对你的项目有用。

Cartopy 无法在旋转网格上正确绘制轮廓数据

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