Re: [Matplotlib-users] real time plotting

[David H. <dh...@gm...>]

I agree, I don't think that will work with mpl's animation stuff or at 
least I wouldn't want to do it that way. I've created GUIs that received 
data from a weather instrument in real-time. I did method 3 that I 
mentioned before because I knew the scientists using it were going to 
want more and more features.

...I FOUND A WAY FOR YOU TO CHEAT:
You can use the Qt "processEvents()" method to have it process 
drawing/painting operation between the event loop iterations. This 
method is frowned upon when doing real Qt GUIs, but eh go for it. If you 
aren't doing anything more serious than watching the output of your 
processing as it goes then try this:

import matplotlib

matplotlib.use('qt4agg')

import matplotlib as mpl

import matplotlib.pyplot as plt
plt.ion()
import numpy as np
from time import sleep
from PyQt4 import QtGui,QtCore
fig=plt.figure()
plt.axis([0,1000,0,1])

i=0
x=list()
y=list()

while i <1000:
     temp_y=np.random.random()
     x.append(i)
     y.append(temp_y)
     plt.scatter(i,temp_y)
     i+=1
     plt.draw()
     sleep(1)
     QtGui.qApp.processEvents()

Good luck,
Dave

On 3/11/13 12:59 PM, Neal Becker wrote:
> I go through a compute loop that takes maybe a few seconds per pass, 
> then plot a new point on the graph.  Do I have to?  No - I thought mpl 
> was supposed to do this and wanted to learn how.  If it really doesn't 
> work I'll do something else.
>
> I don't think animation is correct here - I had the impression 
> animation is where my update would be run as a callback, with a main 
> loop that calls me periodically.  Could that fit the model I 
> described, where a lengthy computation produces a new value every 
> few/10s of seconds?
>
>
> On Mon, Mar 11, 2013 at 1:55 PM, David Hoese <dh...@gm... 
> <mailto:dh...@gm...>> wrote:
>
>     Someone may have to correct me, but I think this has to do with
>     the Qt4 event loop and it not being run properly. When you get
>     into real time plotting it can get kind of tricky. In your case (I
>     got the same results). I have made real-time PyQt4 GUIs before and
>     have always used separate QThreads and Qt signals/slots to update
>     the plot. I've never used GTK so I'm not sure why that worked vs
>     Qt, I would think they would use similar principles but matplotlib
>     does some magic behind the scenes sometimes. You can see different
>     results if you comment out the while loop and import the module
>     into your python/ipython interpreter. After doing this you'll see
>     the figure pop up (you don't even need the fig.canvas.show() for
>     this part if interactive mode is on. I went one step further and
>     turned the while loop into a function:
>
>     def one_iter(i):
>         # Contents of while loop
>
>     Calling this in the interpreter shows the figure updating after
>     each call, but running in a loop (even with sleep) won't show any
>     updates until the loop is done. In my opinion you have a few
>     choices that really depend on your programming comfort level:
>
>     1. Don't make a real-time plot.
>             Do you really need a real-time plot that updates from some
>     external source?
>     2. Maybe you should look at the matplotlib animation functionality
>     (http://matplotlib.org/api/animation_api.html). I like this
>     tutorial:
>     http://jakevdp.github.com/blog/2012/08/18/matplotlib-animation-tutorial/.
>     This won't get you a real-time GUI exactly, but it can help if
>     what you're doing isn't too complicated. It can also be nice for
>     making videos of plot animations.
>     3. If you need a GUI with multiple plots and you need for future
>     feature creep, I would research making PyQt4 GUIs, QThreads, Qt
>     signals and slots, and putting matplotlib figures into a PyQt4
>     GUI. This is complex if you are not familiar with GUI programming
>     and will take a while.
>
>     Sorry I couldn't be of more help, but it really depends on what
>     exactly you are doing.  Mainly, what do you mean by real-time? Do
>     you really mean animation? Let me know what you come up with, I'm
>     interested.
>
>     -Dave
>
>     P.S. Why use a while loop? You can do the same thing with:
>
>         for i in range(1000):
>             # Do stuff
>
>
>     On 3/11/13 10:34 AM, Neal Becker wrote:
>>     I added fig.canvas.show(). It still does nothing.
>>
>>     If I add
>>     mpl.use ('GTK'), now it seems to be doing realtime plotting.
>>
>>     import matplotlib as mpl
>>
>>     import matplotlib.pyplot as plt
>>     plt.ion()
>>     import numpy as np
>>     fig=plt.figure()
>>     plt.axis([0,1000,0,1])
>>
>>     i=0
>>     x=list()
>>     y=list()
>>
>>     fig.canvas.show()
>>     while i <1000:
>>         temp_y=np.random.random()
>>         x.append(i)
>>         y.append(temp_y)
>>         plt.scatter(i,temp_y)
>>         i+=1
>>         plt.draw()
>>
>>
>>
>>     On Mon, Mar 11, 2013 at 10:35 AM, David Hoese <dh...@gm...
>>     <mailto:dh...@gm...>> wrote:
>>
>>         Oops forgot to change the subject line.
>>
>>         On 3/11/13 9:34 AM, David Hoese wrote:
>>
>>             You likely need to "show()" the canvas. I usually do this
>>             by calling "fig.canvas.show()" before the for loop.
>>             Since you are using a Qt4 backend the canvas used by the
>>             figure is a QWidget, the basic component of a Qt4 GUI. I
>>             don't know if there is a more matplotlib specific way of
>>             doing this, but when dealing with a larger system this is
>>             how I do it.
>>
>>             I would also add a sleep ("from time import sleep") of a
>>             couple seconds for testing to make sure you are getting
>>             through the entire for loop before you can see it.
>>
>>             Please CC in any replies, thanks.
>>
>>             -Dave
>>
>>
>>             On 3/11/13 8:58 AM, ndb...@gm...
>>             <mailto:ndb...@gm...> wrote:
>>
>>                 I want to update a plot in real time.  I did some
>>                 goog search, and saw various
>>                 answers.  Trouble is, they aren't working.
>>
>>                 Here's a typical example:
>>
>>                 import matplotlib.pyplot as plt
>>                 import numpy as np
>>                 fig=plt.figure()
>>                 plt.axis([0,1000,0,1])
>>
>>                 i=0
>>                 x=list()
>>                 y=list()
>>
>>                 while i <1000:
>>                      temp_y=np.random.random()
>>                      x.append(i)
>>                      y.append(temp_y)
>>                      plt.scatter(i,temp_y)
>>                      i+=1
>>                      plt.draw()
>>
>>                 If I run this, it draws nothing.
>>
>>                 This is my matplotlibrc:
>>                 backend : Qt4Agg
>>                 mathtext.fontset: stix
>>
>>
>>
>>
>
>