[Matplotlib-users] Polar plot of radar data

[Alexander B. <ale...@gm...>]

Hi all,

 I'm trying to plot some radar data I'm working on, which is presented as a
2048x1440 2D array of ints. This means 2048 azimuth angle values between 0°
and 360°, and 1440 range increments. Array values represent signal return
in that angle/range coordinate. Due to hardware problems, some angle ranges
are missing, there the signal value is zero in the grid.
 The obvious way of plotting this would be a polar grid, so I used a
pcolormesh, like this:




* import numpy as np  import matplotlib.pyplot as plt  *

*  plt.ion()*




*  fig = plt.figure()  ax = fig.add_subplot(111, projection='polar')
theta,rad = np.meshgrid(np.arange(0., 360., 360./scan.shape[0]),
np.arange(scan.shape[1]))   ax.pcolormesh(theta, rad, scan.T)  plt.draw()*

I transposed scan because theta and rad are 1440x2048 arrays, where scan is
a 2048x1440 array.
The resulting image seemed ok, but there were no gaps, which I knew were
there, so I ran the same code without the 'polar' option, and put them side
to side. The result is this:


​In the rectangular plot, there is a gap between around 120° to 160°, which
should be an empty wedge in the polar plot, but it isn't there. Same for
the obvious echos at long range between 0° and 50°. OTOH the plot seems
quite right, with the gating gap around the radar station in the center and
the stronger echos at short range.
 So I'm a bit baffled as to why this doesn't work the way it should. Does
anyone here have an explanation?

-- 
Alex Borghgraef