Dear Michael,
thank you for the tips.
The color solution works fine but the logarithmic scale has some issues.
It is displayed once but I get the following warning:
/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/axes.py:1091:
UserWarning: aspect is not supported for Axes with xscale=linear,
yscale=log
% (xscale, yscale))
the aspect ratio is also clearly wrong and my polar plot looks like an oval.
I think this warning is not very accurate since for a polar plot the
`y' axis means r and this is supposed to be the same in all (real x,y)
directions.
Also it does not seem to remember it's state (which may be due to me
calling ax.clear() to clear the plot when drawing a new batch of
points) and reverts to lineair.
I use the Qt Agg backend and performance seems to be ok.
I would like to fix the axis and not redraw it on every plot (perhaps
using blitting) if possible.
Kind regards,
Pim Schellart
2010/5/4 Michael Droettboom <md...@stsci.edu>:
> Pim Schellart wrote:
>>
>> Hi Everyone,
>>
>> I am currently building an interactive display using matplotlib but I
>> need the following two options.
>> 1. Setting the r axis of a polar plot to logaritmic scale.
>>
>
> axis.set_rscale('log')
>>
>> 2. Setting alpha for each point individually (preferably by giving
>> alpha an array of the same length as the data containing a value
>> between zero and one).
>> Is this currently possible and if not which alternative approach do
>> you recommend.
>>
>
> You can't give alpha an array, but you can create an Nx4 RGBA array (which
> will let you control the color individually, too). For example:
>
> r = np.arange(0, 3.0, 0.01)
> theta = 2*np.pi*r
> c = np.zeros((len(r), 4))
> c[:,0:3] = (1, 0, 0) # red
> c[:,3] = np.arange(0, 1.0, 1.0 / len(r))
> ax.scatter(theta, r, c=c, lw=0)
>>
>> The display needs to plot about a thousand points (using scatter at
>> the moment) roughly updating every second with older points fading
>> away (lower value of alpha).
>>
>
> Scatter is pretty heavily optimized in the *Agg backends, but not so much in
> the others. Make sure you are using Agg and IIRC this level of performance
> should be possible (depending on machine etc., of course).
>
> Mike
>
>
> --
> Michael Droettboom
> Science Software Branch
> Operations and Engineering Division
> Space Telescope Science Institute
> Operated by AURA for NASA
>
>
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