Getting data from a figure

Community matplotlib-users
1

Hi there

I have a function where I want to display an image, get the user to
zoom in on a region of interest, and then return the axes limits.

But the problem is, I can only use it once, the second time it gets
called in a script the figure doesn't appear. I know this is to do
with show() not being supposed to be used multiple times, but I don't
know what I should be doing instead ... any tips? (I'm still new to
python btw)

Also, if there's a better (more pythonic way) to do what I'm doing, I
would appreciate your input. I'm not sure if what I'm doing with the
region variable is dodgy or not.

Currently, I'm doing this:

from pylab import *

def getroi(im):
    imshow(im)
    title('Zoom in to region of interest, then press a key')
    region = array([0, 0, 0, 0]) # Placeholder values

    def keypressed(event):
        region[:] = [round(i) for i in gca().axis()]
        close(gcf())

    # Connect keypressed to event handler
    connect('key_press_event', keypressed)

    show()
    return region

thanks,

Richard

···

--
Richard Brown
Ph.D. Candidate
Dept. of Mechanical Engineering
University of Canterbury, NZ

2

Not sure what region[:] is supposed
to achieve. You are creating a copy with the same name, so you are
over-riding the original variable.

`Hi there

I have a function where I want to display an image, get the user to

zoom in on a region of interest, and then return the axes limits.

But the problem is, I can only use it once, the second time it gets

called in a script the figure doesn’t appear. I know this is to do

with show() not being supposed to be used multiple times, but I don’t

know what I should be doing instead … any tips? (I’m still new to

python btw)

Also, if there’s a better (more pythonic way) to do what I’m doing, I

would appreciate your input. I’m not sure if what I’m doing with the

region variable is dodgy or not.

Currently, I’m doing this:

from pylab import *

def getroi(im):

imshow(im)

title('Zoom in to region of interest, then press a key')

region = array([0, 0, 0, 0]) # Placeholder values

def keypressed(event):

    region[:] = [round(i) for i in gca().axis()]

    close(gcf())

# Connect keypressed to event handler

connect('key_press_event', keypressed)

show()

return region

thanks,

Richard

···

–

Richard Brown

Ph.D. Candidate

Dept. of Mechanical Engineering

University of Canterbury, NZ

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3

Not sure what region[:] is supposed to achieve. You are creating a copy
with the same name, so you are over-riding the original variable.

That doesn't seem to be the case - it returns the right thing on the
first call - i.e. region got changed, but on subsequent calls the
figure is displayed and the function returns array([0,0,0,0]). I
thought taking the slice just gave access to the internals of region
...

How does one assign a new value to a variable in a containing scope?

Richard

···

On 30/03/07, brett.mcsweeney@...1537... <brett.mcsweeney@...1537...> wrote:

Hi there

I have a function where I want to display an image, get the user to
zoom in on a region of interest, and then return the axes limits.

But the problem is, I can only use it once, the second time it gets
called in a script the figure doesn't appear. I know this is to do
with show() not being supposed to be used multiple times, but I don't
know what I should be doing instead ... any tips? (I'm still new to
python btw)

Also, if there's a better (more pythonic way) to do what I'm doing, I
would appreciate your input. I'm not sure if what I'm doing with the
region variable is dodgy or not.

Currently, I'm doing this:

from pylab import *

def getroi(im):
   imshow(im)
   title('Zoom in to region of interest, then press a key')
   region = array([0, 0, 0, 0]) # Placeholder values

   def keypressed(event):
       region[:] = [round(i) for i in gca().axis()]
       close(gcf())

   # Connect keypressed to event handler
   connect('key_press_event', keypressed)

   show()
   return region

thanks,

Richard

4

You can declare the "region" variable as global in keypressed():

def keypressed(event):
    global region
    region = ...

and "region" does not need to get initialized in the containing scope.

Cheers,

  ~ Antonio

···

On 3/30/07, Richard Brown <rgbrown@...287...> wrote:

On 30/03/07, brett.mcsweeney@...1537... > <brett.mcsweeney@...1537...> wrote:
>
> Not sure what region[:] is supposed to achieve. You are creating a copy
> with the same name, so you are over-riding the original variable.
>

That doesn't seem to be the case - it returns the right thing on the
first call - i.e. region got changed, but on subsequent calls the
figure is displayed and the function returns array([0,0,0,0]). I
thought taking the slice just gave access to the internals of region
...

How does one assign a new value to a variable in a containing scope?