Re: [Matplotlib-users] Getting contour positions without interacting with figure/axes

[Thomas R. <tho...@gm...>]

Hi Eric,

Thanks for your help! Unfortunately, ax.set_autoscale_on(False) does not 
work - I had already tried this before unsuccessfully. Consider the 
following:

from pylab import *
import numpy as np

def test():
	fig = figure()
	ax = fig.add_subplot(111)
	a = np.zeros((100,100))
	b = np.zeros((10,10))
	ax.imshow(a)
	ax.set_autoscale_on(False)
	ax.contour(b)
	fig.canvas.draw()

Running test() should result in a subplot with the view interval 0 to 
99, but instead goes from 0 to 9.

Is this normal?

Thanks,

Thomas

Eric Firing wrote:
> Thomas Robitaille wrote:
>> Hello,
>>
>> I am using matplotlib to show an image using:
>>
>> fig = figure()
>> ax = fig.add_subplot(111)
>> ax.imshow(image)
>>
>> After doing this, I want to find the contours for a different image
>> (with different dimensions), but I do not want to interact with the
>> current figure or axes, I just want to retrieve the set of
>> LineCollection objects for the contours. The issue is that if I do
>>
>> c = contour(image2)
>>
>> the contours are stored inside c, but at the same time they are
>> plotted in the current figure. If I use
>>
>> ax.contour(image2)
>>
>> then the contours are not plotted immediately, but the view interval
>> has already been changed inside ax.
>
> The workaround for now may be to call ax.set_autoscale_on(False) before
> your call to ax.contour. You could also save the datalim before and
> restore them afterwards.
>
> This sort of request has come up before, though, and the longer-term
> solution might be some refactoring in contour.py. As it is, everything
> is done when the ContourSet is instantiated; one does not have the
> option of simply calculating the contours, for example.
>
> Eric
>
>>
>> So essentially, I am wondering if it is possible to retrieve a set of
>> LineCollection objects without acting in any way on the current
>> figure/axes.
>
>>
>> Thanks for any help,
>>
>> Thomas
>>
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