python - Matplotlib: draw a selection area in the shape of a rectangle with the mouse

Question

I want to be able to draw a selection area on a matplotlib plot with a mouse event. I didn't find information on how to do it with python.

In the end, I want to be able to draw a region of interest with my mouse on a map created with matplotlib basemap and retrieve the corner coordinates.

Anyone has an idea, example, references?

Thanks,

Greg

class Annotate(object):
  def __init__(self):
      self.ax = plt.gca()
      self.rect = Rectangle((0,0), 1, 1, facecolor='None', edgecolor='green')
      self.x0 = None
      self.y0 = None
      self.x1 = None
      self.y1 = None
      self.ax.add_patch(self.rect)
      self.ax.figure.canvas.mpl_connect('button_press_event', self.on_press)
      self.ax.figure.canvas.mpl_connect('button_release_event', self.on_release)
      self.ax.figure.canvas.mpl_connect('motion_notify_event', self.on_motion)
  def on_press(self, event):
      print 'press'
      self.x0 = event.xdata
      self.y0 = event.ydata    
      self.x1 = event.xdata
      self.y1 = event.ydata
      self.rect.set_width(self.x1 - self.x0)
      self.rect.set_height(self.y1 - self.y0)
      self.rect.set_xy((self.x0, self.y0))
      self.rect.set_linestyle('dashed')
      self.ax.figure.canvas.draw()
  def on_motion(self,event):
      if self.on_press is True:
          return
      self.x1 = event.xdata
      self.y1 = event.ydata
      self.rect.set_width(self.x1 - self.x0)
      self.rect.set_height(self.y1 - self.y0)
      self.rect.set_xy((self.x0, self.y0))
      self.rect.set_linestyle('dashed')
      self.ax.figure.canvas.draw()
  def on_release(self, event):
      print 'release'
      self.x1 = event.xdata
      self.y1 = event.ydata
      self.rect.set_width(self.x1 - self.x0)
      self.rect.set_height(self.y1 - self.y0)
      self.rect.set_xy((self.x0, self.y0))
      self.rect.set_linestyle('solid')
      self.ax.figure.canvas.draw()
      print self.x0,self.x1,self.y0,self.y1
      return [self.x0,self.x1,self.y0,self.y1]

Answer 1

Here's a small example that shows how to use the mouse to draw a rectangle on a matplotlib plot.

import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle

class Annotate(object):
    def __init__(self):
        self.ax = plt.gca()
        self.rect = Rectangle((0,0), 1, 1)
        self.x0 = None
        self.y0 = None
        self.x1 = None
        self.y1 = None
        self.ax.add_patch(self.rect)
        self.ax.figure.canvas.mpl_connect('button_press_event', self.on_press)
        self.ax.figure.canvas.mpl_connect('button_release_event', self.on_release)

    def on_press(self, event):
        print 'press'
        self.x0 = event.xdata
        self.y0 = event.ydata

    def on_release(self, event):
        print 'release'
        self.x1 = event.xdata
        self.y1 = event.ydata
        self.rect.set_width(self.x1 - self.x0)
        self.rect.set_height(self.y1 - self.y0)
        self.rect.set_xy((self.x0, self.y0))
        self.ax.figure.canvas.draw()

a = Annotate()
plt.show()