Realtime plotting

 A nice screen capture video which shows the plotting of a waveform in realtime using python with pylab.

 Now you probably want to know how it is done? The crux with the matplotlib is that you should not call matplotlib functions in any other thread than the main thread. If you dont want to use the  interactive mode of matplotlib (which is another possibility) you have a issue because the main thread normally  keeps running all the time.  Luckily  you can create Timers with the canvas object of the plot, to install periodically called callback functions. In the callback function you can then call whatever matplotlib function you like because the function is executed in the context of the main thread.

 And here  is how it is done:

#!/usr/bin/env python
# Plot a graph of Data which is comming in on the fly
# uses pylab
# Author: Norbert Feurle
# Date: 12.1.2012
# License: if you get any profit from this then please share it with me
import pylab
from pylab import *

xAchse=pylab.arange(0,100,1)
yAchse=pylab.array([0]*100)

fig = pylab.figure(1)
ax = fig.add_subplot(111)
ax.grid(True)
ax.set_title("Realtime Waveform Plot")
ax.set_xlabel("Time")
ax.set_ylabel("Amplitude")
ax.axis([0,100,-1.5,1.5])
line1=ax.plot(xAchse,yAchse,'-')

manager = pylab.get_current_fig_manager()

values=[]
values = [0 for x in range(100)]

Ta=0.01
fa=1.0/Ta
fcos=3.5

Konstant=cos(2*pi*fcos*Ta)
T0=1.0
T1=Konstant

def SinwaveformGenerator(arg):
  global values,T1,Konstant,T0
  #ohmegaCos=arccos(T1)/Ta
  #print "fcos=", ohmegaCos/(2*pi), "Hz"

  Tnext=((Konstant*T1)*2)-T0
  if len(values)%100>70:
    values.append(random()*2-1)
  else:
    values.append(Tnext)
  T0=T1
  T1=Tnext

def RealtimePloter(arg):
  global values
  CurrentXAxis=pylab.arange(len(values)-100,len(values),1)
  line1[0].set_data(CurrentXAxis,pylab.array(values[-100:]))
  ax.axis([CurrentXAxis.min(),CurrentXAxis.max(),-1.5,1.5])
  manager.canvas.draw()
  #manager.show()

timer = fig.canvas.new_timer(interval=20)
timer.add_callback(RealtimePloter, ())
timer2 = fig.canvas.new_timer(interval=20)
timer2.add_callback(SinwaveformGenerator, ())
timer.start()
timer2.start()

pylab.show()

 As a next step i embedded some Tkinter Widgets into the plot to make the number of points to view and the Waveform generation speed more adjustable:

The Code:

#!/usr/bin/env python
# Plot a graph of Data which is comming in on the fly
# uses pylab
# Author: Norbert Feurle
# Date: 12.1.2012
# License: if you get any profit from this then please share it with me  and only use it for good
import pylab
from pylab import *
import Tkinter
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg, NavigationToolbar2TkAgg

root = Tkinter.Tk()
root.wm_title("Extended Realtime Plotter")

xAchse=pylab.arange(0,100,1)
yAchse=pylab.array([0]*100)

fig = pylab.figure(1)
ax = fig.add_subplot(111)
ax.grid(True)
ax.set_title("Realtime Waveform Plot")
ax.set_xlabel("Time")
ax.set_ylabel("Amplitude")
ax.axis([0,100,-1.5,1.5])
line1=ax.plot(xAchse,yAchse,'-')

canvas = FigureCanvasTkAgg(fig, master=root)
canvas.show()
canvas.get_tk_widget().pack(side=Tkinter.TOP, fill=Tkinter.BOTH, expand=1)

toolbar = NavigationToolbar2TkAgg( canvas, root )
toolbar.update()
canvas._tkcanvas.pack(side=Tkinter.TOP, fill=Tkinter.BOTH, expand=1)

values=[]
values = [0 for x in range(100)]

Ta=0.01
fa=1.0/Ta
fcos=3.5

Konstant=cos(2*pi*fcos*Ta)
T0=1.0
T1=Konstant

def SinwaveformGenerator():
  global values,T1,Konstant,T0,wScale2
  #ohmegaCos=arccos(T1)/Ta
  #print "fcos=", ohmegaCos/(2*pi), "Hz"

  Tnext=((Konstant*T1)*2)-T0 
  if len(values)%100>70:
    values.append(random()*2-1)
  else:
    values.append(Tnext)
  T0=T1
  T1=Tnext
  root.after(int(wScale2['to'])-wScale2.get(),SinwaveformGenerator)

def RealtimePloter():
  global values,wScale,wScale2
  NumberSamples=min(len(values),wScale.get())
  CurrentXAxis=pylab.arange(len(values)-NumberSamples,len(values),1)
  line1[0].set_data(CurrentXAxis,pylab.array(values[-NumberSamples:]))
  ax.axis([CurrentXAxis.min(),CurrentXAxis.max(),-1.5,1.5])
  canvas.draw()
  root.after(25,RealtimePloter)
  #canvas.draw()

  #manager.show()

def _quit():
    root.quit()     # stops mainloop
    root.destroy()  # this is necessary on Windows to prevent
                    # Fatal Python Error: PyEval_RestoreThread: NULL tstate

button = Tkinter.Button(master=root, text='Quit', command=_quit)
button.pack(side=Tkinter.BOTTOM)

wScale = Tkinter.Scale(master=root,label="View Width:", from_=3, to=1000,sliderlength=30,length=ax.get_frame().get_window_extent().width, orient=Tkinter.HORIZONTAL)
wScale2 = Tkinter.Scale(master=root,label="Generation Speed:", from_=1, to=200,sliderlength=30,length=ax.get_frame().get_window_extent().width, orient=Tkinter.HORIZONTAL)
wScale2.pack(side=Tkinter.BOTTOM)
wScale.pack(side=Tkinter.BOTTOM)

wScale.set(100)
wScale2.set(wScale2['to']-10)

root.protocol("WM_DELETE_WINDOW", _quit)  #thanks aurelienvlg
root.after(100,SinwaveformGenerator)
root.after(100,RealtimePloter)
Tkinter.mainloop()
#pylab.show()