title: Real time trajectory plotting - Matplotlib
body: <p>I want to plot a trajectory using matplotlib. In each iteration of a program I wrote, I obtain the x and y coordinates of an object. I would like to draw the movement of this object on an xy graph. I used the following code:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  from matplotlib.path import Path
  import matplotlib.patches as patches
  import time
  
  fig = plt.figure()
  ax = fig.add_subplot(111)
  ax.set_xlim(-100,100)
  ax.set_ylim(-100,100)
  plt.ion()
  plt.show(block=True)
  
  verts = [
      (0, 0), #I'm just assuming two sets of points here. I actually intend to put variables here which I can update in real time.
      (27, 0)
      ]
  
  codes = [Path.MOVETO,
           Path.LINETO]  
  
  path = Path(verts, codes)
  
  #fig = plt.figure()
  #ax = fig.add_subplot(111)
  patch = patches.PathPatch(path, facecolor='white', lw=2)
  ax.add_patch(patch)
  #ax.set_xlim(-100,100)
  #ax.set_ylim(-100,100)
  plt.draw()
  time.sleep(1)
  </code></pre>
  
  <p>But all I can see is a blank window with two axes. Yes, I did change the order of the codes to suit my needs (see commented lines) since for real time, I would need to put this in a loop. Can anyone help me out here? Also, if I don't use "patch", the lines become invisible. Is there another way around?</p>