Plotting some values to a polar graph in matplotlib

Question

I want to plot some values representing visible satellites into a polar graph with Python and matplotlib. I have written some code following a matplotlib example, and the polar chart is represented, but given points are not plotted:

import matplotlib
from matplotlib.pyplot import figure, show, rc, grid
from math import pi

# radar green, solid grid lines
rc('grid', color='#316931', linewidth=1, linestyle='-')
rc('xtick', labelsize=15)
rc('ytick', labelsize=15)

# force square figure and square axes looks better for polar, IMO
width, height = matplotlib.rcParams['figure.figsize']
size = min(width, height)
# make a square figure
fig = figure(figsize=(size, size))
ax = fig.add_axes([0.1, 0.1, 0.8, 0.8], polar=True, axisbg='#d5de9c')

# Satellite info [PRN, E, Az, Ss, Used (1 yes, 0 no)]
sat = [ [1, 62, 255, 46, 1],
        [14, 62, 26, 46, 1],
        [31, 42, 158, 36, 1],
        [22, 40, 76, 50, 1],
        [11, 29, 308, 0, 0],
        [19, 26, 243, 36, 1],
        [3, 13, 217, 0, 0],
        [18, 10, 93, 0, 0],
        [20, 6, 291, 0, 0],
        [5, 1, 72, 0, 0],
        [122, 43, 216, 0, 0],
        [135, 47, 203, 43, 0] ]

for index in (0, len(sat)-1):
    if(sat[index][4]>0):
        ax.plot(sat[index][2], sat[index][1], color='green', marker='s', markersize=12)
    else:
        ax.plot(sat[index][2], sat[index][1], color='gray', marker='s', markersize=12)

ax.set_rmax(2.0)
grid(True)

ax.set_title("Visible satellites", fontsize=20)
show()

What am I doing wrong?

Rutger Kassies · Accepted Answer · 2012-10-18 11:30:09Z

1

Its simpler to just iterate of your list of sats like this:

for s in sat:
    if(s[4]>0):
        ax.plot(s[2], s[1],color='green', marker='s', markersize=5)
    else:
        ax.plot(s[2], s[1],color='gray', marker='s', markersize=5)

In addition to that, you're also limiting the azimuth to <2 with the set_rmax, this leaves only 1 satellite visible, uncomment it to see all of them.

edit: Directly unpacking the list might further improve the readability:

for (PRN, E, Az, Ss, Used) in sat:
    if(Used>0):
        ax.plot(Ss, Az,color='green', marker='s', markersize=5)
    else:
        ax.plot(Ss, Az,color='gray', marker='s', markersize=5)

edited Oct 18, 2012 at 11:30

answered Oct 18, 2012 at 11:24

Rutger Kassies

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3 Comments

Roman Rdgz Over a year ago

I love that Direct unpacking. I didn't know that what possible with Python! Thanks! :)

Roman Rdgz Over a year ago

The problem was the set_rmax as you said. I still have one extra doubt: is it possible to put a label to each represented point?

Rutger Kassies Over a year ago

Sure, you can call the .text method on the ax, given the code above it would become:

for (PRN, E, Az, Ss, Used) in sat:     if(Used>0):         ax.plot(Ss, Az,color='green', marker='s', markersize=5)     else:         ax.plot(Ss, Az,color='gray', marker='s', markersize=5)     ax.text(Ss, Az, PRN, color='red', size=15)

ev-br · Accepted Answer · 2012-10-18 11:20:55Z

1

in this line:

for index in (0, len(sat)-1):

index only runs over a pair of values. Have you meant the range for index in range(0, len(sat))?

answered Oct 18, 2012 at 11:20

ev-br

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