Polar Contour Plot-分箱形状不匹配

Question

I would like to plot a polar contour-map of azimuthal and zenith angles obtained from XYZ data. But the arrays I pass into the contourf function are misshapen and I'm not sure how to correct this?

import numpy as np
import matplotlib.pyplot as plt

# Populated arrays with angles.
azimuths = np.random.random(200)*360
zeniths = np.random.random(200)*180

a_bins = np.linspace(0,360,13)
z_bins = np.linspace(0,180,7)

grid, ae, ze = np.histogram2d(azimuths, zeniths, bins=[a_bins,z_bins])

a_bins = np.radians(a_bins)
r, theta = np.meshgrid(z_bins, a_bins)

# Plot
fig, ax = plt.subplots(subplot_kw=dict(projection='polar'))
cax = ax.contourf(theta, r, grid, 30)
cb = fig.colorbar(cax)

plt.show()

The code runs but throws the following warning: Shape of x does not match that of z: found (13, 7) instead of (12, 6).

Now I think I understand the error. The bins are 13 for azimuths (0-360) and 7 for zeniths (0-180). The matrix returned by histogram2d function has a shape of (12,6) because this is the number of slots between the edges. I'm just not sure how to fix the binning.

Answer 1

One way is to expand the grid array to be the same shape as theta and r . This is necessary so that the polar plot extends all the way around (and matches up at theta=0 .

import numpy as np
import matplotlib.pyplot as plt

# Populated arrays with angles.
azimuths = np.random.random(200)*360
zeniths = np.random.random(200)*180

a_bins = np.linspace(0,360,13)
z_bins = np.linspace(0,180,7)

grid, ae, ze = np.histogram2d(azimuths, zeniths, bins=[a_bins,z_bins])

a_bins = np.radians(a_bins)
r, theta = np.meshgrid(z_bins, a_bins)

# Extend grid by one column row, using the 0th column and row
g = np.zeros(r.shape)
g[:-1,:-1] = grid 
g[-1] = g[0]      # copy the top row to the bottom
g[:,-1] = g[:,0]  # copy the left column to the right
print g.shape,r.shape,theta.shape
### (13, 7) (13, 7) (13, 7)

# Plot
fig, ax = plt.subplots(subplot_kw=dict(projection='polar'))
cax = ax.contourf(theta, r, g, 30)
cb = fig.colorbar(cax)

plt.show()