Re: [Matplotlib-users] pyplot: Extract contourset without plotting

[Benjamin R. <ben...@ou...>]

On Thursday, January 27, 2011, Paul Ivanov <piv...@gm...> wrote:
> Daniel Fulger, on 2011-01-27 18:16,  wrote:
>> Dear all,
>>
>> contourset = pyplot.contour(..)
>>
>> calculates the contourset but also grabs whatever figure is currently
>> active *somewhere* in the entire code
>> and whichever scope it was created. The contours are plotted into it.
>>
>> While I could possibly live with that, I would really like to
>> suppress any plotting and grabbig of focus. Only the contourset
>> should be calculated.
>>
>> I can't find anything that describes this. Everybody wants the plot,
>> not me.
>>
>> I would like to avoid hte workaround  to ask for the currently active
>> figure (if!! there is one at all), store the number, and later return
>> focus. Is there no switch parameter (in pyplot or for contour at
>> least) that turns plotting off?
>
> Hi Daniel,
>
> I'm not sure if this gets at what you're asking for, but if
> you just want the contours plotted on a figure other than the
> currently active one, grab a handle to some other axes and call
> contour from the axes itself (the parameters are the same).
> Here's what I mean:
>
> -----------
> f,ax  =plt.subplots(1,1) #grab handles to figure and axes
> # or, if you're using an older version of matplotlib, do:
> # f=plt.figure();ax=plt.subplot(1,1,1)
>
>
> f2,ax2  =plt.subplots(1,1) # "f" no longer active figure
> ...
> contourset = ax.contour(...) # draw to the old figure "f"
> -----------
>
> You can read more about the difference between using pyplot and
> using the object-oriented api here:
>
> http://matplotlib.sourceforge.net/faq/usage_faq.html
>
> On the other hand, if you just want the contour to not show up,
> you can pass it alpha=0.0 to make it completely transparent and
> invisible (but it's still there)
>
> contourset = pyplot.contour(.., alpha=0.0)
> # later call contourset.set_alpha(1.0) to make visible again
>
> best,
> --
> Paul Ivanov
> 314 address only used for lists,  off-list direct email at:
> http://pirsquared.org | GPG/PGP key id: 0x0F3E28F7
>

I believe he would rather call the core function that contour uses to
do the heavy lifting.  This was something that one can do in matlab,
btw.  I don't have access to the source right now.  What does contour
call to perform this calculation?

Ben Root