I have a problem replacing axis labels in Matplotlib. I want to change the parameters of the radial axis on my polar graph.
Basically, I calculate the cylinder distortion, which is nothing but the radius deviates from the original (perfectly circular) cylinder. Some of the distortion values are negative, while some of them are positive due to tensile and compressive forces. I'm looking for a way to represent this in cylindrical coordinates graphically, so I thought the best option would be a polar plot. Excel gives me a "radar chart" that is flexible enough so that I can specify the minimum and maximum values of the radial axis. I want to reproduce this in Python using Matplotlib.
My Python script for building on polar coordinates is as follows.
#!usr/bin/env python import matplotlib.pyplot as plt import numpy as np x = np.arange(-180.0,190.0,10) theta = (np.pi/180.0 )*x # in radians offset = 2.0 R1 = [-0.358,-0.483,-0.479,-0.346,-0.121,0.137,0.358,0.483,0.479,0.346,0.121,\ -0.137,-0.358,-0.483,-0.479,-0.346,-0.121,0.137,0.358,0.483,0.479,0.346,0.121,\ -0.137,-0.358,-0.483,-0.479,-0.346,-0.121,0.137,0.358,0.483,0.479,0.346,0.121,\ -0.137,-0.358] fig1 = plt.figure() ax1 = fig1.add_axes([0.1,0.1,0.8,0.8],polar=True) ax1.set_rmax(1) ax1.plot(theta,R1,lw=2.5)
My plot is as follows: 
But I do not want to imagine it. I want to change my radial axis so that I can show the data as a deviation from some reference value, say -2. How can I ask Matplotlib to change the label of the minimum axis in polar coordinates? I can do it VERY easily in Excel. I select a minimum radial value of -2 to get the following Excel radar chart:
In Python, I can easily compensate for my input by 2. My new dataset is called R2, as shown:
#!usr/bin/env python import matplotlib.pyplot as plt import numpy as np x = np.arange(-180.0,190.0,10) theta = (np.pi/180.0 )*x # in radians offset = 2.0 R2 = [1.642,1.517,1.521,1.654,1.879,2.137,2.358,2.483,2.479,2.346,2.121,1.863,\ 1.642,1.517,1.521,1.654,1.879,2.137,2.358,2.483,2.479,2.346,2.121,1.863,1.642,\ 1.517,1.521,1.654,1.879,2.137,2.358,2.483,2.479,2.346,2.121,1.863,1.642] fig2 = plt.figure() ax2 = fig2.add_axes([0.1,0.1,0.8,0.8],polar=True) ax2.plot(theta,R2,lw=2.5) ax2.set_rmax(1.5*offset) plt.show()
The graph is shown below:
As soon as I get this, I TOGETHER add axis labels and write it to my script. But this is a really ugly way. Is there any way that I can directly get the Matplotlib equivalent of an Excel radar chart and change the axis label labels without having to manipulate my input?