add_cyclic_point

全球の描画で，極投影系の地図投影および経度の始まりが図の端に来ない場合に，経度の始まり・終わりの場所で，図に切れ目が入ってしまう．これを防ぐには，cartopy.util.dd_cyclic_pointで，経度方向にもう一点，格子点を加える．

import cartopy.crs as ccrs

import cartopy.feature as cfeature

import cartopy.util as cutil

import xarray as xr

import numpy as np

from matplotlib import pyplot as plt

lons1d=np.arange(-179.5,180,1.0)

lats1d=np.arange(-89.5,90,1.0)

xsz=len(lons1d)

ysz=len(lats1d)

lons2d=np.ones([ysz,1]) @ lons1d.reshape(1,xsz)

lats2d=lats1d.reshape(ysz,1) @ np.ones([1,xsz])

vals=lats2d*np.cos(lons2d/360*2*np.pi)

plt.ion()

lon_fig_mid=240

plt.figure(1)

ax1=plt.subplot(2,1,1, projection=ccrs.LambertCylindrical(central_longitude=lon_fig_mid))

img1=ax1.contourf(lons1d,lats1d,vals,transform=ccrs.PlateCarree())

ax1.add_feature(cfeature.COASTLINE,edgecolor='brown')

vals_c, lons_c = cutil.add_cyclic_point(vals, coord=lons1d)

ax1=plt.subplot(2,1,2, projection=ccrs.LambertCylindrical(central_longitude=lon_fig_mid))

img1=ax1.contourf(lons_c,lats1d,vals_c,transform=ccrs.PlateCarree())

ax1.add_feature(cfeature.COASTLINE,edgecolor='brown')