我正在尝试绘制卫星沿其轨道的最大(理论)视场。我正在使用底图,我想在底图上沿着轨道绘制不同位置(有散点图),并且我想使用tissot方法(或等效方法)添加整个视场。 下面的代码可以正常工作,直到纬度在300公里的高度轨道上达到北约75度为止。除此之外,代码还会输出ValueError: “ ValueError:未定义的反短程线(可能是反点)”
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
import math
earth_radius = 6371000. # m
fig = plt.figure(figsize=(8, 6), edgecolor='w')
m = Basemap(projection='cyl', resolution='l',
llcrnrlat=-90, urcrnrlat=90,
llcrnrlon=-180, urcrnrlon=180)
# draw the coastlines on the empty map
m.drawcoastlines(color='k')
# define the position of the satellite
position = [300000., 75., 0.] # altitude, latitude, longitude
# radius needed by the tissot method
radius = math.degrees(math.acos(earth_radius / (earth_radius + position[0])))
m.tissot(position[2], position[1], radius, 100, facecolor='tab:blue', alpha=0.3)
m.scatter(position[2], position[1], marker='*', c='tab:red')
plt.show()
要注意的是,该代码在南极(纬度低于-75)处工作正常。我知道这是一个已知的错误,是否存在此问题的已知解决方法? 感谢您的帮助!
答案 0 :(得分:3)
您发现的是底图的一些限制。现在让我们切换到Cartopy。工作代码将有所不同,但差别不大。
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import math
earth_radius = 6371000.
position = [300000., 75., 0.] # altitude (m), lat, long
radius = math.degrees(math.acos(earth_radius / (earth_radius + position[0])))
print(radius) # in subtended degrees??
fig = plt.figure(figsize=(12,8))
img_extent = [-180, 180, -90, 90]
# here, cartopy's' `PlateCarree` is equivalent with Basemap's `cyl` you use
ax = fig.add_subplot(1, 1, 1, projection = ccrs.PlateCarree(), extent = img_extent)
# for demo purposes, ...
# let's take 1 subtended degree = 112 km on earth surface (*** you set the value as needed ***)
ax.tissot(rad_km=radius*112, lons=position[2], lats=position[1], n_samples=64, \
facecolor='red', edgecolor='black', linewidth=0.15, alpha = 0.3)
ax.coastlines(linewidth=0.15)
ax.gridlines(draw_labels=False, linewidth=1, color='blue', alpha=0.3, linestyle='--')
plt.show()
使用上面的代码,结果图为:
现在,如果我们使用正交投影,(用此替换相关的代码行)
ax = fig.add_subplot(1, 1, 1, projection = ccrs.Orthographic(central_longitude=0.0, central_latitude=60.0))
您得到以下情节: