Re: [Matplotlib-users] ginput with undefined number of points

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

On Thu, Jun 7, 2012 at 9:07 AM, David Craig <dcd...@gm...> wrote:

>  Hi,
> I trying to define an area in a pcolor plot (several plots) using the
> ginput(). However since it is an irregular shape and will be different in
> each plot so I cant define how many points there will be before hand, I've
> tried the following but it requires a double click at each point, which I
> would like to avoid as it duplicates points
>
> x = randn(10,10)
> imshow(x)
>
> button = False
> points = []
> while button == False:
>     points.append(ginput(1))
>     button = waitforbuttonpress()
>
> Anyone know a better way to go about this??
> thanks
> Dave
>
>
I would utilize the event handling mechanism within mpl to do this.  You
can create a function that would append the xy coordinates to points at
each call.  Here is a mockup.


def on_press(event) :
    on_press.points.append((event.xdata, event.ydata))

on_press.points = []

Then, you would need some way to indicate that you want to start and
finish, such as some sort of key press:

def key_press(event) :
    if event.key == 'a' :
        if key_press.active :
            key_press.mouse_cid =
key_press.fig.canvas.mpl_connect('button_press_event', on_press)
        else :
            key_press.fig.canvas.mpl_disconnect(key_press.mouse_cid)
        key_press.active = not key_press.active

key_press.active = False
key_press.fig = plt.figure()
key_press.fig.canvas.mpl_connect('key_press_event', key_press)


There are some more elegant ways of doing this, particularly by creating
some sort of object to hold these variables, but this is a quick and dirty
way of doing it.

I hope that helps!
Ben Root