如何放大cartopy.crs.Orthographic中的特定纬度？

如何解决如何放大cartopy.crs.Orthographic中的特定纬度？

我不确定这是否可行，但我基本上是在尝试在正交地图中隔离北极圈纬度 (60N) 并保持椭圆体，而不是将放大的图像设为矩形/正方形。

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这是我所拥有的：

fig = plt.figure(figsize=[20,10])

ax1 = plt.subplot(1,1,projection=ccrs.Orthographic(0,90))

for ax in [ax1]:
    ax.coastlines(zorder=2)
    ax.stock_img()
    ax.gridlines()

这给出了我想要的北极视图，但我希望它停在 60N。

Current yield

解决方法

要获得正交地图的放大和方形范围，您需要绘制一些控制点（例如，使用 .scatter）或在投影坐标中指定正确的 extent（更困难）。这是要尝试的代码。

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

fig = plt.figure(figsize=[8,8])

lonlatproj = ccrs.PlateCarree()
my_projn = ccrs.Orthographic(central_longitude=0,central_latitude=90)

ax1 = plt.subplot(1,1,projection=my_projn)

# set `lowlat` as lower limits of latitude to plot some points
# these points will determine the plot extents of the map
lowlat = 60 + 2.8   # and get 60
lons,lats = [-180,-90,90],[lowlat,lowlat,lowlat]
# plot invisible points to get map extents
ax1.scatter(lons,lats,s=0,color='r',transform=lonlatproj)
#ax1.stock_img()  #uncomment to get it plotted
ax1.coastlines(lw=0.5,zorder=2)
ax1.gridlines(lw=2,ec='black',draw_labels=True)

方法二：通过在投影坐标中指定正确的范围

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

fig = plt.figure(figsize=[8,projection=my_projn)

# These 2 lines of code grab extents in projection coordinates
_,y_min = my_projn.transform_point(0,60,lonlatproj)  #(0.0,-3189068.5)
x_max,_ = my_projn.transform_point(90,lonlatproj) #(3189068.5,0)

# prep extents of the axis to plot map
pad = 25000
xmin,xmax,ymin,ymax = y_min-pad,x_max+pad,y_min-pad,x_max+pad
# set extents with prepped values
ax1.set_extent([xmin,ymax],crs=my_projn) # data/projection coordinates

ax1.stock_img()
ax1.coastlines(lw=0.5,zorder=2)

# plot other layers of data here using proper values of zorder

# finally,plot gridlines
ax1.gridlines(draw_labels=True,x_inline=False,y_inline=True,color='k',linestyle='dashed',linewidth=0.5)
plt.show()

方法三用圆形边界绘制地图

可运行代码：

import cartopy.crs as ccrs
import matplotlib.pyplot as plt
import matplotlib.path as mpath
import numpy as np

r_limit = 3214068.5 #from: ax.get_ylim() of above plot

# some settings  
lonlatproj = ccrs.PlateCarree()
my_projn = ccrs.Orthographic(central_longitude=0,central_latitude=90)
fig = plt.figure(figsize=[8,8])
ax = plt.subplot(1,projection=my_projn)

# add bluemarble image
ax.stock_img()
# add coastlines
ax.coastlines(lw=0.5,color="black",zorder=20)


# draw graticule (of meridian and parallel lines)
gls = ax.gridlines(draw_labels=True,crs=ccrs.PlateCarree(),lw=3,color="gold",xlocs=range(-180,180,30),ylocs=range(-80,91,10))


# add extra padding to the plot extents
r_extent = r_limit*1.0001
ax.set_xlim(-r_extent,r_extent)
ax.set_ylim(-r_extent,r_extent)


# Prep circular boundary
circle_path = mpath.Path.unit_circle()
circle_path = mpath.Path(circle_path.vertices.copy() * r_limit,circle_path.codes.copy())

#set circle boundary
ax.set_boundary(circle_path)
#hide frame
ax.set_frame_on(False)  #hide the rectangle frame

plt.show()