Store mouse click event coordinates with matplotli

问题:

I am trying to implement a simple mouse click event in matplotlib. I wish to plot a figure then use the mouse to select the lower and upper limits for integration. So far I am able to print the coordinates to screen but not store them for later use in the program. I would also like to exit the connection to the figure after the second mouse click.

Below is the code which currently plots and then prints the coordinates.

My Question(s):

How can I store coordinates from the figure to list? i.e. click = [xpos, ypos]

Is it possible to get two sets of x coordinates in order to do a simple integration over that section of line?

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(-10,10)
y = x**2

fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x,y)

def onclick(event):
    global ix, iy
    ix, iy = event.xdata, event.ydata
    print 'x = %d, y = %d'%(
        ix, iy)

    global coords
    coords = [ix, iy]

    return coords


for i in xrange(0,1):

    cid = fig.canvas.mpl_connect('button_press_event', onclick)


plt.show()

回答1:

mpl_connect needs to be called just once to connect the event to event handler. It will start listening to click event until you disconnect. And you can use

fig.canvas.mpl_disconnect(cid)

to disconnect the event hook.

What you want to do is something like:

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(-10,10)
y = x**2

fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(x,y)

coords = []

def onclick(event):
    global ix, iy
    ix, iy = event.xdata, event.ydata
    print 'x = %d, y = %d'%(
        ix, iy)

    global coords
    coords.append((ix, iy))

    if len(coords) == 2:
        fig.canvas.mpl_disconnect(cid)

    return coords
cid = fig.canvas.mpl_connect('button_press_event', onclick)

回答2:

Thanks to otterb for providing the answer! I've added in a little function taken from here... Find nearest value in numpy array

In all this code will plot, wait for selection of x points and then return the indices of the x array needed for any integration, summations etc.

Ta,

import numpy as np
import matplotlib.pyplot as plt
from scipy.integrate import trapz

def find_nearest(array,value):
    idx = (np.abs(array-value)).argmin()
    return array[idx]

# Simple mouse click function to store coordinates
def onclick(event):
    global ix, iy
    ix, iy = event.xdata, event.ydata

    # print 'x = %d, y = %d'%(
    #     ix, iy)

    # assign global variable to access outside of function
    global coords
    coords.append((ix, iy))

    # Disconnect after 2 clicks
    if len(coords) == 2:
        fig.canvas.mpl_disconnect(cid)
        plt.close(1)
    return


x = np.arange(-10,10)
y = x**2

fig = plt.figure(1)
ax = fig.add_subplot(111)
ax.plot(x,y)

coords = []

# Call click func
cid = fig.canvas.mpl_connect('button_press_event', onclick)

plt.show(1)


# limits for integration
ch1 = np.where(x == (find_nearest(x, coords[0][0])))
ch2 = np.where(x == (find_nearest(x, coords[1][0])))

# Calculate integral
y_int = trapz(y[ch1[0][0]:ch2[0][0]], x = x[ch1[0][0]:ch2[0][0]])

print ''
print 'Integral between '+str(coords[0][0])+ ' & ' +str(coords[1][0])
print y_int

回答3:

I have a similar need, but this code does not work for me. I have copy/pasted it directly (Anaconda 2.7) but it appears fig.canvas.mpl_connect('button_press_event', onclick) never waits for input, which triggers error in the coords[n][m] calls that follow it. Suggestions?

> Traceback (most recent call last):
> 
>   File "<ipython-input-5-d074e6221b24>", line 1, in <module>
>     runfile('C:/Users/xxx/Documents/Python/test/untitled0.py', wdir='C:/Users/xxx/Documents/Python/test')
> 
>   File
> "C:\Anaconda2\lib\site-packages\spyder\utils\site\sitecustomize.py",
> line 705, in runfile
>     execfile(filename, namespace)
> 
>   File
> "C:\Anaconda2\lib\site-packages\spyder\utils\site\sitecustomize.py",
> line 87, in execfile
>     exec(compile(scripttext, filename, 'exec'), glob, loc)
> 
>   File "C:/Users/xxx/Documents/Python/test/untitled0.py", line
> 45, in <module>
>     ch1 = np.where(x == (find_nearest(x, coords[0][0])))
> 
> IndexError: list index out of range