How to make smooth circles on basemap projections in Matplotlib by Python

问题

I'm not advanced user of Python, but due to my scientific work I got tasks to plot some graphs with Matplotlib. Now I have to draw smooth-deformed according to the basemap projection, circles around given point. But in the result I got circles with broken lines:

import numpy as np
import matplotlib.pyplot as plt

def plot_mwd(RA,Dec,org=0,title='GCS', projection='aitoff'):

    x = np.remainder(RA+360-org,360) # shift RA values
    ind = x>180
    x[ind] -=360    # scale conversion to [-180, 180]
    x=-x    # reverse the scale: East to the left
    tick_labels = np.array([150, 120, 90, 60, 30, 0, 330, 300, 270, 240, 210])
    tick_labels = np.remainder(tick_labels+360+org,360)
    fig = plt.figure(figsize=(10, 5))
    ax = fig.add_subplot(111, projection=projection, axisbg ='LightCyan')
    ax.scatter(np.radians(x),np.radians(Dec), s = 30, c = 'k', marker = '.')  # convert degrees to radians
    ax.set_xticklabels(tick_labels)     # we add the scale on the x axis
    ax.set_title(title)
    ax.title.set_fontsize(15)
    ax.xaxis.label.set_fontsize(12)
    ax.yaxis.label.set_fontsize(12)
    ax.grid(color='tab:gray', linestyle='-', linewidth=0.2)
    circle1 = plt.Circle((np.radians(35),np.radians(30)), np.radians(40), color='g', fill = False) # Circle parameters
    fig = plt.gcf()
    ax = fig.gca()
    ax.add_artist(circle1)

coord = np.array([(325,30)]) # coordinates that will be ploted
plot_mwd(coord[:,0],coord[:,1], org=0, title ='GCS', projection ='aitoff')   

plt.show()

回答1:

The function plt.Circle() does not allow to specify the number of vertexes to plot. So, you need to write up your own code. Here is my code that you may try:

# Plot circle with 36 vertexes
phi = np.linspace(0, 2.*np.pi, 36)  #36 points
r = np.radians(40)
x = np.radians(35) + r*np.cos(phi)
y = np.radians(30) + r*np.sin(phi)
ax.plot(x, y, color="g")

Use my code in place of yours 2 lines:

circle1 = plt.Circle((np.radians(35), np.radians(30)), np.radians(40), color='g', fill = False)  # Circle parameters
ax.add_artist(circle1)

The resulting image:

来源：https://stackoverflow.com/questions/48950420/how-to-make-smooth-circles-on-basemap-projections-in-matplotlib-by-python