使用 matplotlib-basemap 对多个绘图使用一张背景图？

Question

Matplotlibs 底图模块具有为地图绘制背景的能力，具有inbuilt functions for some basic maps 和绑定到arcgis maps 的能力。

两个选项都运行良好，但速度很慢 (see also here)，尤其是 arcgis 选项。

对于单个地块，这不是一个大问题，但是对于多个地块（在我的情况下大约 500 个），这变得相当等待练习，另外，我不想向 arcgis 发送数百个请求，这总是无论如何都要获取相同的地图。

但是我如何设置/下载一次背景地图，并在绘制多个版本的循环中继续使用它？

我已经调整了 the great circle example from the documentation 与 etopo 背景，并通过一些颜色循环进行测试：

from mpl_toolkits.basemap import Basemap
import numpy as np
import matplotlib.pyplot as plt
# create new figure, axes instances.
fig=plt.figure()
ax=fig.add_axes([0.1,0.1,0.8,0.8])
# setup mercator map projection.
m = Basemap(llcrnrlon=-100.,llcrnrlat=20.,urcrnrlon=20.,urcrnrlat=60.,\
            rsphere=(6378137.00,6356752.3142),\
            resolution='l',projection='merc',\
            lat_0=40.,lon_0=-20.,lat_ts=20.)
# nylat, nylon are lat/lon of New York
nylat = 40.78; nylon = -73.98
# lonlat, lonlon are lat/lon of London.
lonlat = 51.53; lonlon = 0.08
# draw great circle route between NY and London
m.drawcoastlines()
m.etopo()
# draw parallels
m.drawparallels(np.arange(10,90,20),labels=[1,1,0,1])
# draw meridians
m.drawmeridians(np.arange(-180,180,30),labels=[1,1,0,1])

colors = ('r','b','k','y')
for p_color in colors:
    m.drawgreatcircle(nylon,nylat,lonlon,lonlat,linewidth=2,color=p_color)
    filename = '%s.png' % p_color
    plt.savefig(filename, dpi=100)

上述方法有效，但这只是因为我没有关闭情节。用我的真实数字，我很快就会耗尽记忆。如果我在循环末尾添加plt.close()，我的背景图就会丢失。当我将情节的设置放入循环时也是如此：

from mpl_toolkits.basemap import Basemap
import numpy as np
import matplotlib.pyplot as plt
# create new figure, axes instances.
# setup mercator map projection.
m = Basemap(llcrnrlon=-100.,llcrnrlat=20.,urcrnrlon=20.,urcrnrlat=60.,\
            rsphere=(6378137.00,6356752.3142),\
            resolution='l',projection='merc',\
            lat_0=40.,lon_0=-20.,lat_ts=20.)
# nylat, nylon are lat/lon of New York
nylat = 40.78; nylon = -73.98
# lonlat, lonlon are lat/lon of London.
lonlat = 51.53; lonlon = 0.08
# draw great circle route between NY and London
m.drawcoastlines()
m.etopo()
# draw parallels
m.drawparallels(np.arange(10,90,20),labels=[1,1,0,1])
# draw meridians
m.drawmeridians(np.arange(-180,180,30),labels=[1,1,0,1])

colors = ('r','b','k','y')
for p_color in colors:
    fig=plt.figure()
    ax=fig.add_axes([0.1,0.1,0.8,0.8])
    m.drawgreatcircle(nylon,nylat,lonlon,lonlat,linewidth=2,color=p_color)
    filename = '%s.png' % p_color
    plt.savefig(filename, dpi=100)
    plt.close()

当我在循环中执行整个m.Basemap…、m.etopo 内容时，它似乎才起作用（忽略第一个选项的内存问题），但这太慢了。

如何设置“m”一次并继续使用它？

我可以通过绘制背景图一次，将我的数据绘制到透明背景上，然后将其与 imagemagick 结合来实现 MacGyver，但我觉得应该有更好的解决方案。

Answer 1

我想这个想法是保留底图而不是改变它。在循环中添加您想要从图像更改为图像的艺术家，保存图形，然后删除艺术家。

from mpl_toolkits.basemap import Basemap
import numpy as np
import matplotlib.pyplot as plt
# create new figure, axes instances.
# setup mercator map projection.
fig=plt.figure()
ax=fig.add_axes([0.1,0.1,0.8,0.8])
m = Basemap(llcrnrlon=-100.,llcrnrlat=20.,urcrnrlon=20.,urcrnrlat=60.,\
            rsphere=(6378137.00,6356752.3142),\
            resolution='l',projection='merc',\
            lat_0=40.,lon_0=-20.,lat_ts=20.)
# nylat, nylon are lat/lon of New York
nylat = 40.78; nylon = -73.98
# lonlat, lonlon are lat/lon of London.
lonlat = 51.53; lonlon = 0.08
# draw great circle route between NY and London
m.drawcoastlines()
m.etopo()
# draw parallels
m.drawparallels(np.arange(10,90,20),labels=[1,1,0,1])
# draw meridians
m.drawmeridians(np.arange(-180,180,30),labels=[1,1,0,1])

colors = ('r','b','k','y')
for p_color in colors:
    gc = m.drawgreatcircle(nylon,nylat,lonlon,lonlat,linewidth=2,color=p_color)
    filename = 'output{}.png'.format(p_color)
    plt.savefig(filename, dpi=100)
    # remove previous plot from axes
    for line in gc:
        line.remove()
    del gc