12

I am completely new to Python. Therefore don't get too mad at me, because I am sure that there are basic things that I am missing. Here is my problem:

I am trying to extract mouse-click coordinates from an image and use those coordinates as variables.

The code allows to import and image, from which I want to extract the coordinates. Some prompts ask the user about size and extent of the diagram, after which I would like to set up a coordinate grid by clicking the origin, and the end point on the x- and y-axes respectively. The idea is to use these 3 sets of coordinates and transform them into Pressure and Temperature coordinates through some transformation functions (see code).

# Determine the origin by clicking
# Probably with classes??
class Origin:
    def getorigin(eventorigin):
          eventorigin.x0 = eventorigin.x
          eventorigin.y0 = eventorigin.y
    #mouseclick event
    w.bind("<Button 1>",getorigin)
# What do I do here??
x0 = ...
y0 = ...

I don't really know how to assign the coordinates that I get through clicking, to a new variable that I can use later in the code.

I can print the coordinates, but since they are a function, they are local and are not usable outside of the function (as far as I could understand). So, and approach using classes might be better, but I have no idea how to do that.

Any help is appreciated.

FULL CODE (ADAPTED):

from tkinter import *
from tkinter.filedialog import askopenfilename
from PIL import Image, ImageTk
import tkinter.simpledialog

root = Tk()

#setting up a tkinter canvas
w = Canvas(root, width=1000, height=1000)
w.pack()

#adding the image
File = askopenfilename(parent=root, initialdir="./",title='Select an image')
original = Image.open(File)
original = original.resize((1000,1000)) #resize image
img = ImageTk.PhotoImage(original)
w.create_image(0, 0, image=img, anchor="nw")

#ask for pressure and temperature extent
xmt = tkinter.simpledialog.askfloat("Temperature", "degrees in x-axis")
ymp = tkinter.simpledialog.askfloat("Pressure", "bars in y-axis")

#ask for real PT values at origin
xc = tkinter.simpledialog.askfloat("Temperature", "Temperature at origin")
yc = tkinter.simpledialog.askfloat("Pressure", "Pressure at origin")

#instruction on 3 point selection to define grid
tkinter.messagebox.showinfo("Instructions", "Click: \n" 
                                            "1) Origin \n"
                                            "2) Temperature end \n"
                                            "3) Pressure end")

# From here on I have no idea how to get it to work...

# Determine the origin by clicking
def getorigin(eventorigin):
    global x0,y0
    x0 = eventorigin.x
    y0 = eventorigin.y
    print(x0,y0)
#mouseclick event
w.bind("<Button 1>",getorigin)

# Determine the extent of the figure in the x direction (Temperature)
def getextentx(eventextentx):
    global xe
    xe = eventextentx.x
    print(xe)
#mouseclick event
w.bind("<Button 1>",getextentx)

# Determine the extent of the figure in the y direction (Pressure)
def getextenty(eventextenty):
    global ye
    ye = eventextenty.y
    print(ye)
#mouseclick event
w.bind("<Button 1>",getextenty)

#message to confirm that the grid is set up
tkinter.messagebox.showinfo("Grid", "Grid is set. You can start picking coordinates.")

#Coordinate transformation into Pressure-Temperature space
def printcoords(event):
    xmpx = xe-x0
    xm = xmt/xmpx
    ympx = ye-y0
    ym = -ymp/ympx

    #coordinate transformation
    newx = (event.x-x0)*(xm)+xc
    newy = (event.y-y0)*(ym)+yc

    #outputting x and y coords to console
    print (newx,newy)
#mouseclick event
w.bind("<Button 1>",printcoords)

root.mainloop()
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2 Answers 2

Reset to default
9

If what I said in my previous comment is what you're trying to do, since tkinter doesn't pause the program to wait for a mouse click event you will have to do this: it rebinds it every time the mouse button get clicked

from tkinter import *
from tkinter.filedialog import askopenfilename
from PIL import Image, ImageTk
import tkinter.simpledialog

root = Tk()

#setting up a tkinter canvas
w = Canvas(root, width=1000, height=1000)
w.pack()

#adding the image
File = askopenfilename(parent=root, initialdir="./",title='Select an image')
original = Image.open(File)
original = original.resize((1000,1000)) #resize image
img = ImageTk.PhotoImage(original)
w.create_image(0, 0, image=img, anchor="nw")

#ask for pressure and temperature extent
xmt = tkinter.simpledialog.askfloat("Temperature", "degrees in x-axis")
ymp = tkinter.simpledialog.askfloat("Pressure", "bars in y-axis")

#ask for real PT values at origin
xc = tkinter.simpledialog.askfloat("Temperature", "Temperature at origin")
yc = tkinter.simpledialog.askfloat("Pressure", "Pressure at origin")

#instruction on 3 point selection to define grid
tkinter.messagebox.showinfo("Instructions", "Click: \n" 
                                            "1) Origin \n"
                                            "2) Temperature end \n"
                                            "3) Pressure end")

# From here on I have no idea how to get it to work...

# Determine the origin by clicking
def getorigin(eventorigin):
    global x0,y0
    x0 = eventorigin.x
    y0 = eventorigin.y
    print(x0,y0)
    w.bind("<Button 1>",getextentx)
#mouseclick event
w.bind("<Button 1>",getorigin)

# Determine the extent of the figure in the x direction (Temperature)
def getextentx(eventextentx):
    global xe
    xe = eventextentx.x
    print(xe)
    w.bind("<Button 1>",getextenty)

# Determine the extent of the figure in the y direction (Pressure)
def getextenty(eventextenty):
    global ye
    ye = eventextenty.y
    print(ye)
    tkinter.messagebox.showinfo("Grid", "Grid is set. You can start picking coordinates.")
    w.bind("<Button 1>",printcoords)

#Coordinate transformation into Pressure-Temperature space
def printcoords(event):
    xmpx = xe-x0
    xm = xmt/xmpx
    ympx = ye-y0
    ym = -ymp/ympx

    #coordinate transformation
    newx = (event.x-x0)*(xm)+xc
    newy = (event.y-y0)*(ym)+yc

    #outputting x and y coords to console
    print (newx,newy)

root.mainloop()
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2 Comments

WOW, that seems to do what I want (I might have to adapt my transformations, but the program is otherwise fine!) I am doing some other stuff right now, but will test and comment later. Thanks!
Everything works. Thanks! (only had to change ympx=ye-y0 to ympx=y0-ye to flip the coordinate system (but that has nothing to do with the question, ahaha).
3

The easiest way is to set x, y to global, class or not doesn't matter. I didn't see your full code because I can't open zip files on my phone. So here's what I can help with your example

import tkinter as tk
def getorigin(eventorigin):
      global x,y
      x = eventorigin.x
      y = eventorigin.y
      print(x,y)

root = tk.Tk()
root.bind("<Button 1>",getorigin)
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6 Comments

I adapted the code. The piece itself seem to work, but in the context of the full code it doesn't. If I try print(x,y) at the end, the error message NameError: name 'x' is not defined is showed. Could it be that I need some kind of an if statement or loop in order to be able to save the 3 coordinates one after the other?
Here is the adapted version of the full code
@Lele do you mind copy and paste your adapted code to your question under EDIT. I am on my phone so I can't view .py files
@Lele you can only bind "<Button 1>" once using w.bind. Doing so repeatedly just replace the previous bind
Are you're trying to make the program to wait for the user to press something? Then continue to wait for the user to press something else again?
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