2D polar surface plot

Community matplotlib-users
1

Stephane,

First off, you probably do not want to use a surface plot. Rather, pcolor might be more appropriate.

In addition, if you can take the azimuth-range coordinates and convert that into x-y coordinates, you can then plot a pcolor using just that. The code would look something like so (assuming some function polar2xy exists):

azimuth, r, vals, x, and y are all the same shape

x, y = polar2xy(azimuth, r)
plt.pcolor(x, y, vals)
plt.show()

Once that is working sufficiently, then you will have to modify the code a bit to specify the colormap.

I hope that gets you started.

Ben Root

···

On Tue, Jun 15, 2010 at 10:17 AM, Stephane GONAUER <stephane.gonauer@…3160…> wrote:

Hi,

After reading documentations and the
matplotlib example I haven’t found a way to graph the plot I want.

I am trying to display a radar video (one
turn of the antenna at a time). As such I need to plot a polar surface in 2D
with a colormap indicating the video intensity.

My data input is simply a file where
intensity are logged along rho and theta

The nearest example I found in the
documentation is the 3d-surface plot but I need to have it in 2D

Can you provide me with some idea/pointers ?

Has it been already tried ?

Best Regards,

Stéphane

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2

pcolor runs directly on polar plots just fine.� No need to convert
polar to cartesian outside of matplotlib.

#!/usr/bin/env python

from pylab import *

import numpy as np

Sampling 60 points in both dimensions

T = linspace(0, np.pi * 2, 60)

R = linspace(0, 1.0, 60)

Z = rand(60,60)

Create a polar axes

ax = subplot(111, projection=‘polar’)

pcolor plot onto it

c = ax.pcolor(T, R, Z)

title(‘default: no edges’)

show()

Mike

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-- Michael Droettboom
Science Software Branch
Space Telescope Science Institute
Baltimore, Maryland, USA
3

2010/6/16 Michael Droettboom <mdroe@...86...>:

pcolor runs directly on polar plots just fine. No need to convert polar to
cartesian outside of matplotlib.

It's true, but at the expense of pretty much time, since the arcs must
be rendered properly. If your data is dense enough in r and phi, a
handmade conversion would probably gain much speedup. Of course you
loose then also the nice polar diagram axes ... I tried this once in
polar with pixel-dense data (in a 400x400 px figure) and it takes
really forever.

I don't know if the output of the fast versions of pcolor is properly
rendered in polar axes?

Friedrich