[Matplotlib-users] Re: Polar plots of radar scans (OT)

[Travis E. O. <oli...@ie...>]

Jeff Whitaker wrote:
> Stephens, A (Ag) wrote:
> 
>
> Ag:  You should be able to use either contourf or pcolor to make the 
> plot by just passing it the X and Y coordinates of the radial distance, 
> azimuth points.  Here's a simple example:
> 
> from pylab import *
> deltatheta = 2.*pi/100.

> theta = arange(0.,2.*pi,deltatheta)
> R = arange(0.,pi,deltatheta)
> r,t = meshgrid(R, theta)

I see this kind of code a lot on this list.  I just want to point out 
that in NumPy (and Numeric and Numarray) you don't have to completely 
generate the "meshgrid" like this because of broadcasting.  All you need 
is for r to be Nx1 and t to be 1xN  and the broadcasting will take care 
of it so that Z, X, and Y below are all NxN.   This can save space and 
time particularly for large values of N.

In NumPy (and old SciPy) there is even a simple constructor for these 
"open" grids:

r,t = ogrid[0:pi:deltatheta, 0:2*pi:deltatheta]

would replace the three lines above.


> Z = sin(r)*sin(3.*t)
> X = r*cos(t)
> Y = r*sin(t)
> figure(figsize=(8,8))
> cs = contourf(X, Y, Z)
> title('Simple polar contour plot')
> show()


Sorry for the somewhat off-topic post.

-Travis