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Or more specifically, how can I change the [659] on the upper-right corner to '659 degrees' or something like that ?

enter image description here

I have checked all the threads mentioned in the following reply: matplotlib values under cursor. However, all of them seem to address the x,y location of the cursor. I am interested in changing the data-value. I could not find a reply or related documentation in the api.

I have tried both format_coord(x, y) and format_cursor_data(data) but neither of them seem to be working.

Thanks, Sarith

PS: My code is in multiple modules and is a part of gui application. I can share relevant sections if that would be of any help in answering this.

Community
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Sarith Subramaniam
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  • The weird thing is that usually it doesn' even show x and y coordinates, so you must already have a function for that.. – Jan Mar 27 '16 at 07:18

4 Answers4

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One line solution: 

ax.format_coord = lambda x, y: 'x={:.2f}, y={:.2f}, z={:.2f}'.format(x,y,data[int(y + 0.5),int(x + 0.5)])
bmr
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I had the same problem (I wanted to get rid of the data and send it to somewhere else in a tkinter widget). I figured out the ax.format_coord was'nt being called, the one you have to change is the one at matplotlib.artist.Artist this worked for me:

    def format_cursor_data(self,data):            
        return 'new_data'
    matplotlib.artist.Artist.format_cursor_data=format_cursor_data
Miguel Núñez
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  • You also can reassign this function onto AxesImage object returned from imshow: img = p.imshow(my_image); img.format_cursor_data = format_cursor_data – Homper Dec 06 '19 at 16:35
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By modifying an example from matplotlib I got this code:

This displays x,y, and z value with a degrees after z.

You should be able to easily modify it, or copy the relevant functions to make it work on your side.

You said you already tried format_coord, maybe you forgot to set the funtion? (second last line)

"""
Show how to modify the coordinate formatter to report the image "z"
value of the nearest pixel given x and y
"""
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.cm as cm

X = 10*np.random.rand(5, 3)

fig, ax = plt.subplots()
ax.imshow(X, cmap=cm.jet, interpolation='nearest')

numrows, numcols = X.shape


def format_coord(x, y):
    col = int(x + 0.5)
    row = int(y + 0.5)
    if col >= 0 and col < numcols and row >= 0 and row < numrows:

        #get z from your data, given x and y
        z = X[row, col]

        #this only leaves two decimal points for readability
        [x,y,z]=map("{0:.2f}".format,[x,y,z])

        #change return string of x,y and z to whatever you want
        return 'x='+str(x)+', y='+str(y)+', z='+str(z)+" degrees"
    else:
        return 'x=%1.4f, y=%1.4f' % (x, y)

#Set the function as the one used for display
ax.format_coord = format_coord
plt.show()
Jan
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  • Hi, thanks for replying. But this doesn't do it. It just displays something like "x=0.01, y=0.02 z=0.40 degrees [3.4]" (which is actually confusing). What I meant was something like than "x=0.01, y=0.02, 3.4 degrees". Perhaps I am asking for too much :/ – Sarith Subramaniam Mar 27 '16 at 08:01
  • Where do you get the [3.4] from? Is it automatically generated? Try changing `return 'x='+str(x)+', y='+str(y)+', z='+str(z)+" degrees"` to `return 'x='+str(x)+', y='+str(y)+', z='+"Deg: "`. This should then at least display `"x=0.01, y=0.02, Deg: [3.4] "` – Jan Mar 27 '16 at 08:28
  • Well, it just shows up on its own. I am using matplotlib 1.5.1. Here is the screenshot from your code: https://www.dropbox.com/s/aim7h7o866ht4oq/Untitled.jpg?dl=0 – Sarith Subramaniam Mar 27 '16 at 08:57
  • @SarithSubramaniam well that is... weird. You could remove `str(z)` resulting in `"x=0.01, y=0.02, degrees [3.4] "`. I would guess there is a code fragment somewhere which causes this, because I can't get it to appear on my matplotlib :/ – Jan Mar 27 '16 at 14:29
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    This is one of the new features in 1.5. The `[]` are hard-coded into the move callback in the `Toolbar` (https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/backend_bases.py#L2826 ). You could sub-class and override that method or monkey-patch the `format_cursor_data` method on your image artist. – tacaswell Mar 27 '16 at 16:50
  • @tcaswell Thank you ! That meets my requirement perfectly. If you post this as a reply, I will accept that as the answer. – Sarith Subramaniam Mar 27 '16 at 19:46
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Emmm, Sarith, I am also facing the problem but a little trick helped me out. I still used this function:

your_imshow.format_coord = lambda x, y: 'x={:.5f}, y={:.2f}, amplitude='.format(x,y)

It pretends to add label before the bracket. Yeah, it is an easy but not essential way to change the presentation form, but it works to me. I hope this could also benefit others.

Wenyin Wei
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