Change Axis Direction in Matplotlib

Introduction

In this lab, you will learn how to change the axis direction in a Matplotlib plot using the set_axis_direction() method. This method allows you to change the direction of an axis to any of the four cardinal directions: top, bottom, left, or right.

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Importing Libraries

First, we need to import the necessary libraries for this lab. We will be using numpy and matplotlib.

import matplotlib.pyplot as plt
import numpy as np

Setting up the Plot

Next, we will define a function setup_axes() that will set up the polar projection in a rectangular box. This function uses GridHelperCurveLinear to create a polar projection with a rectangular box.

from matplotlib.projections import PolarAxes
from matplotlib.transforms import Affine2D
import mpl_toolkits.axisartist as axisartist
import mpl_toolkits.axisartist.angle_helper as angle_helper
import mpl_toolkits.axisartist.grid_finder as grid_finder
from mpl_toolkits.axisartist.grid_helper_curvelinear import \
    GridHelperCurveLinear

def setup_axes(fig, rect):
    """Polar projection, but in a rectangular box."""
    grid_helper = GridHelperCurveLinear(
        Affine2D().scale(np.pi/180., 1.) + PolarAxes.PolarTransform(),
        extreme_finder=angle_helper.ExtremeFinderCycle(
            20, 20,
            lon_cycle=360, lat_cycle=None,
            lon_minmax=None, lat_minmax=(0, np.inf),
        ),
        grid_locator1=angle_helper.LocatorDMS(12),
        grid_locator2=grid_finder.MaxNLocator(5),
        tick_formatter1=angle_helper.FormatterDMS(),
    )
    ax = fig.add_subplot(
        rect, axes_class=axisartist.Axes, grid_helper=grid_helper,
        aspect=1, xlim=(-5, 12), ylim=(-5, 10))
    ax.axis[:].toggle(ticklabels=False)
    ax.grid(color=".9")
    return ax

Adding Floating Axis

We will define two functions that will add floating axes to our plot. The first function add_floating_axis1() adds a floating axis to the plot with a label of theta = 30. The second function add_floating_axis2() adds a floating axis to the plot with a label of r = 6.

def add_floating_axis1(ax):
    ax.axis["lat"] = axis = ax.new_floating_axis(0, 30)
    axis.label.set_text(r"$\theta = 30^{\circ}$")
    axis.label.set_visible(True)
    return axis

def add_floating_axis2(ax):
    ax.axis["lon"] = axis = ax.new_floating_axis(1, 6)
    axis.label.set_text(r"$r = 6$")
    axis.label.set_visible(True)
    return axis

Changing the Axis Direction

Now, we will create a loop to set up four different plots with the floating axis in each of the four cardinal directions. In the loop, we will use add_floating_axis1() and add_floating_axis2() to add the floating axes, and set_axis_direction() to set the axis direction.

fig = plt.figure(figsize=(8, 4), layout="constrained")

for i, d in enumerate(["bottom", "left", "top", "right"]):
    ax = setup_axes(fig, rect=241+i)
    axis = add_floating_axis1(ax)
    axis.set_axis_direction(d)
    ax.set(title=d)

for i, d in enumerate(["bottom", "left", "top", "right"]):
    ax = setup_axes(fig, rect=245+i)
    axis = add_floating_axis2(ax)
    axis.set_axis_direction(d)
    ax.set(title=d)

plt.show()

Viewing the Plot

Finally, we will view the plot. We can see the same plot with the floating axis in each of the four cardinal directions.

Summary

In this lab, you learned how to change the axis direction in a Matplotlib plot using the set_axis_direction() method. By using this method, you can easily change the direction of an axis to any of the four cardinal directions: top, bottom, left, or right.