plotting a Gauge with python and matplotlib

Nicolas Fauchereau

Friday 10 Oct. 2014


In [12]:
%matplotlib inline

In [13]:
import matplotlib
from matplotlib import cm
from matplotlib import pyplot as plt
import numpy as np

In [14]:
from matplotlib.patches import Circle, Wedge, Rectangle

some function definitions

In [15]:
def degree_range(n): 
    start = np.linspace(0,180,n+1, endpoint=True)[0:-1]
    end = np.linspace(0,180,n+1, endpoint=True)[1::]
    mid_points = start + ((end-start)/2.)
    return np.c_[start, end], mid_points

In [16]:
def rot_text(ang): 
    rotation = np.degrees(np.radians(ang) * np.pi / np.pi - np.radians(90))
    return rotation

main gauge function

In [17]:
def gauge(N=5, labels=['LOW','MEDIUM','HIGH','VERY HIGH','EXTREME'], colors='jet_r', cat=1, title='', fname='./meter.png'): 
    some sanity checks first
    if len(labels) != N: 
        print("number of labels not equal to number of categories\n")
    if colors is a string, we assume it's a matplotlib colormap
    and we discretize
    if isinstance(colors, str):
        cmap = cm.get_cmap(colors, N)
        cmap = cmap(np.arange(N))
        colors = cmap[::-1,:].tolist()
    if isinstance(colors, list): 
        if len(colors) == N:
            colors = colors[::-1]
            print("number of colors not equal to number of categories\n")

    begins the plotting
    fig, ax = plt.subplots()

    ang_range, mid_points = degree_range(N)

    labels = labels[::-1]
    plots the sectors and the arcs
    patches = []
    for ang, c in zip(ang_range, colors): 
        # sectors
        patches.append(Wedge((0.,0.), .4, *ang, facecolor='w', lw=2))
        # arcs
        patches.append(Wedge((0.,0.), .4, *ang, width=0.10, facecolor=c, lw=2, alpha=0.5))
    [ax.add_patch(p) for p in patches]

    set the labels (e.g. 'LOW','MEDIUM',...)

    for mid, lab in zip(mid_points, labels): 

        ax.text(0.35 * np.cos(np.radians(mid)), 0.35 * np.sin(np.radians(mid)), lab, \
            horizontalalignment='center', verticalalignment='center', fontsize=14, \
            fontweight='bold', rotation = rot_text(mid))

    set the bottom banner and the title
    r = Rectangle((-0.4,-0.1),0.8,0.1, facecolor='w', lw=2)
    ax.text(0, -0.05, title, horizontalalignment='center', \
         verticalalignment='center', fontsize=22, fontweight='bold')

    plots the arrow now
    pos = mid_points[abs(cat - N)]
    ax.arrow(0, 0, 0.225 * np.cos(np.radians(pos)), 0.225 * np.sin(np.radians(pos)), \
                 width=0.04, head_width=0.09, head_length=0.1, fc='k', ec='k')
    ax.add_patch(Circle((0, 0), radius=0.02, facecolor='k'))
    ax.add_patch(Circle((0, 0), radius=0.01, facecolor='w', zorder=11))

    removes frame and ticks, and makes axis equal and tight
    fig.savefig(fname, dpi=200)


In [18]:
gauge(N=5, labels=['LOW','MEDIUM','HIGH','VERY HIGH','EXTREME'], colors='jet_r', cat=5, title='scary thing here', fname='./gauge.png')