Plotting real-time on Raspberry Pi with python and wxWidget

Question

I'm trying to plot some data coming from the sensor on banana pi. For simplicity of development I use python and wxWidget. To plot the data I use matplotlib library. It's doing ok on my laptop, but when I launch it on banana pi, the plot is drawn very slow.

def on_redraw_timer(self, event):
    print datetime.datetime.now()
    self.data.append(getCurrentValue())
    self.draw_plot()

This code is executed every 100 ms and this is what it outputs

2016-03-06 10:51:47.530607
2016-03-06 10:51:47.880988
2016-03-06 10:51:48.211054
2016-03-06 10:51:48.538298
2016-03-06 10:51:48.864935
2016-03-06 10:51:49.190108
2016-03-06 10:51:49.514287
2016-03-06 10:51:49.851634
2016-03-06 10:51:50.178744
2016-03-06 10:51:50.503762

So it takes 300 ms to draw the plot. Which is unacceptable. Is it possible to fasten the drawing speed? Or should I use some other libraries?

Thank you!

jhoepken · Accepted Answer · 2016-03-06 11:22:22Z

1

I think that there is no real way of speeding things up on the banana pi. Keep in mind that you are using a tiny CPU with a very limited amount of RAM for the same application you usually use your laptop for. I'm not saying that you cannot run a GUI on the banana pi or use matplotlib, but the 100ms replot frequency is a little bit tough, as you have already experienced on your own. Especially since you run an operating system (linux, I guess) with a window manager that takes it's toll on the RAM and CPU as well.

As a suggestion, could you use your existing python script to extract the data and use gnuplot to display it? This could work at that frequency. There is even a gnuplot python interface, but this will most likely not solve your 300ms plot delay problem.

answered Mar 6, 2016 at 11:22

jhoepken

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4 Comments

user1354033 Over a year ago

yeah banana-pi is tought. do you think perfomance would be better if I use C++ instead of python? and use some low level C++ libraries to draw graphs?

jhoepken Over a year ago

I would check if you can constantly visualize the data with gnuplot, while the existing python methods do the data extraction, before I spend more time on coding. Otherwise you port everything to C++ and then it's the same thing, but in C++.

jhoepken Over a year ago

Was this helpful to you?

jhoepken Over a year ago

Have a look at caswenson.com/2008_02_22_python_gnuplot_gnuplotpy, the documentation as such is pretty sparse.

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