Getting contour positions without interacting with figure/axes

Thomas_Robitaille1 · February 21, 2009, 2:00pm

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.

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

Eric_Firing1 · February 21, 2009, 7:34pm

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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Thomas_Robitaille1 · February 22, 2009, 10:32pm

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

------------------------------------------------------------------------------

Open Source Business Conference (OSBC), March 24-25, 2009, San
Francisco, CA
-OSBC tackles the biggest issue in open source: Open Sourcing the
Enterprise
-Strategies to boost innovation and cut costs with open source
participation
-Receive a $600 discount off the registration fee with the source
code: SFAD
http://p.sf.net/sfu/XcvMzF8H
_______________________________________________
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Eric_Firing1 · February 22, 2009, 10:45pm

Thomas Robitaille wrote:

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?

On my system, it does go from 0-99. What mpl version are you using? I made the change to using autoscale_view in the ContourSet initializer, which obeys the setting by set_autoscale_on, on November 17. Prior to that, xlim and ylim were being set directly, so the workaround if you have an earlier version would be to save those values (using ax.get_xlim(), ax.get_ylim()) and then restore them with ax.set_xlim etc.

Eric

···

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

------------------------------------------------------------------------------

Open Source Business Conference (OSBC), March 24-25, 2009, San
Francisco, CA
-OSBC tackles the biggest issue in open source: Open Sourcing the
Enterprise
-Strategies to boost innovation and cut costs with open source
participation
-Receive a $600 discount off the registration fee with the source
code: SFAD
http://p.sf.net/sfu/XcvMzF8H
_______________________________________________
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Matplotlib-users@lists.sourceforge.net
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Thomas_Robitaille1 · February 22, 2009, 10:47pm

Hi Eric,

I'm using matplotlib 0.98 (which comes with the Enthought distribution) so that would explain why there was an issue.

Thanks for your help!

Thomas

Eric Firing wrote:

···

Thomas Robitaille wrote:

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?

On my system, it does go from 0-99. What mpl version are you using? I
made the change to using autoscale_view in the ContourSet initializer,
which obeys the setting by set_autoscale_on, on November 17. Prior to
that, xlim and ylim were being set directly, so the workaround if you
have an earlier version would be to save those values (using
ax.get_xlim(), ax.get_ylim()) and then restore them with ax.set_xlim etc.

Eric

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

------------------------------------------------------------------------------

Open Source Business Conference (OSBC), March 24-25, 2009, San
Francisco, CA
-OSBC tackles the biggest issue in open source: Open Sourcing the
Enterprise
-Strategies to boost innovation and cut costs with open source
participation
-Receive a $600 discount off the registration fee with the source
code: SFAD
http://p.sf.net/sfu/XcvMzF8H
_______________________________________________
Matplotlib-users mailing list
Matplotlib-users@lists.sourceforge.net
matplotlib-users List Signup and Options