CODEWITHSUNDEEP
pythonmatplotlibmouseevent
achille
achille

Reputation: 661

Preventing execution until points are selected on matplotlib graph

I want to select 4 points on a matplotlib graph and operate on those points as soon as 4 four points are clicked on. The code below will indeed store the 4 points in the variable points but does not wait for the four points to be selected. I tried adding a for loop and tried threading here but neither option worked. How can I solve this problem?

fig = plt.figure()
ax = fig.add_subplot(111)
image = np.load('path-to-file.npy')
tfig = ax.imshow(image)
points = []

def onclick(event):
    global points
    points.append((event.xdata, event.ydata))

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

# this line will cause an error because the four points haven't been
# selected yet
firstPoint = points[0]

Upvotes: 2

Views: 39

Answers (1)

Joe Kington
Joe Kington

Reputation: 284602

In this case, you might consider using plt.ginput instead of "rolling your own".

As a quick example:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.set(title='Select 4 points')

xy = plt.ginput(4)
x, y = zip(*xy)

ax.fill(x, y, color='lightblue')
ax.plot(x, y, ls='', mfc='red', marker='o')

plt.show()

Upvotes: 1

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