How to add an encircling axes around a polar plot?

Question

I'm trying to figure out how to append an axes to my polar projection. The newly added axes is supposed to wrap around the original polar axes like a ring.

For that purpose I tried to use append_axes from a divider created via make_axes_locatable on a polar matplotlib projection ax.

However, there's no option for "outer" or anything that would resemble polar projections with the append_axes arguments. Instead of a ring around the axes, I get a new axes just below the original one (see picture).

Is there any alternative that would allow creating an axes of ring shape around an existing polar axes?

Note, I don't want to add them on the same ax because the scales may be different.

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import make_axes_locatable

plt.style.use("seaborn-white")
def synthesize(polar=False):
    fig = plt.figure()
    ax = fig.add_subplot(111, polar=polar)
    t = np.linspace(0,2*np.pi)
    r_sin = np.sin(t)
    r_cos = np.cos(t)
    for r in [r_sin, r_cos]:
        ax.scatter(t, r, c=r, s=t*100, edgecolor="white", cmap=plt.cm.magma_r)
        ax.scatter(t, -r, c=r, s=t*100, edgecolor="white", cmap=plt.cm.magma_r)
    ax.set_title("polar={}".format(polar),fontsize=15)
    ax.set_xticklabels([])
    return fig, ax, t

# Rectilinear
fig, ax, t = synthesize(polar=False)
# Here are the plot dimensions in response to the answer below
xlim = ax.get_xlim()
ylim = ax.get_ylim()
rlim = (ax.get_rmin(), ax.get_rmax())
print(xlim, ylim, rlim)
(0.0, 6.283185307179586) (0.0, 2.2437621373846617) (0.0, 2.2437621373846617)
# Encircling axis
divider = make_axes_locatable(ax)
ax_below = divider.append_axes("bottom", size="32.8%", pad=0.1)
ax_below.scatter(t, np.tan(t), c="black", edgecolor="white")

# Polar
fig, ax, t = synthesize(polar=True)
divider = make_axes_locatable(ax)
ax_below = divider.append_axes("bottom", size="32.8%", pad=0.1)
ax_below.scatter(t, np.tan(t), c="black", edgecolor="white")

I reworded your question, such that it doesn't ask for something that is simply not possible, i.e. instead of "How do I do ?", you'd ask "How do I get ? I tried , but it fails." — ImportanceOfBeingErnest, Feb 21 '19 at 21:56
This wording sounds much better! Thank you. I wasn't aware that the method above is specific for rectangular plots. — O.rka, Feb 21 '19 at 21:59

score 2 · Answer 1 · answered Feb 23 '19 at 22:48

You probably can do something by tunning set_rmax and set_rorigin like this:

import numpy as np
import matplotlib.pyplot as plt

plt.style.use("seaborn-white")
def synthesize(polar=False):
    fig = plt.figure()
    ax = fig.add_subplot(111, polar=polar)
    ax.set_rmax(30)
    t = np.linspace(0,2*np.pi)
    r_sin = np.sin(t)
    r_cos = np.cos(t)
    for r in [r_sin, r_cos]:
        ax.scatter(t, r, c=r, s=t*100, edgecolor="white", cmap=plt.cm.magma_r)
        ax.scatter(t, -r, c=r, s=t*100, edgecolor="white", cmap=plt.cm.magma_r)
    ax.set_title("polar={}".format(polar),fontsize=15)
    ax.set_xticklabels([])
    return fig, ax, t

# Polar
fig, ax, t = synthesize(polar=True)
ax_below = fig.add_subplot(111, polar=True, frameon=True)

# ax_below = divider.append_axes("bottom", size="32.8%", pad=0.1)
ax_below.scatter(t, np.tan(t), c="black", edgecolor="white")
ax_below.set_rorigin(-75)
ax_below.set_rmin(-25)
plt.show()

Just by trial and error, the -25 because the lower plot seems to go from -25 to 25, the -75 means that the center of the circle is at the point -75, along qith the -25 leaves 50 units to the plot in the bottom. It definetly depends on what you want to show in the plot though. — vlizana, Feb 24 '19 at 03:22
I'm wondering there is a good way to automate it w/ the ax.get_xlim() style methods? — O.rka, Feb 24 '19 at 03:38

How to add an encircling axes around a polar plot?

1 Answers1