How to speed up real time plotting in pyqtgraph

Question

In short, I'm trying to find a faster way to plot real time data coming through a serial input. The data looks like a coordinate (x,y) and about 40 are coming in each second. The stream will store the data in a array, using x as the index and setting y as the value for it. This portion is being threaded. While the stream can read in data immediatley, the pyqtgraph library isn't able to keep up with this speed.

Here's the portion of the code where I am plotting the data. The distances and theta variables are arrays with 6400 indexes. They have been transformed into polar values and plotted with each iteration. I added a delay there just to help keep it real-time, though it's only a temporary solution.

while True:
    x = distances * np.cos(theta)
    y = distances * np.sin(theta)
    plot.plot(x, y, pen=None, symbol='o', clear=True)
    pg.QtGui.QApplication.processEvents()


    #sleep(0.025)

While it's going the way I expect it to, it's not able to plot the most recent data from the serial input. It's easily several seconds behind from the most recent reads, probably because it can not plot 6400 points every 1/40 of a second. I'm wondering if there's a way to only update 1 point rather than having to re-plot the entire scatter every time in pyqtgraph.

It may be possible to plot based on point, but if so, is there a way to keep track of each individual point? There should be no point that shares the same angle value and have different distances, and should essentially overwrite it.

I'm also wondering if there are other graphing animation libraries out there that may be a possible solution worth considering.

This is what it looks like, if you're wondering:

Answer 1

Threading allows you to always have data available to plot but the plot speed is bottlenecked due to the paintEvent latency for each plot iteration. From my understanding, there is no way to update 1 point per paint event with setData instead of having to replot the entire data set for each iteration. So if you have 6400, you must repaint all points even if you are updating the just data with 1 additional point.

Potential workarounds to this include downsampling your data or to only plot once every X amount of data points. Essentially, you are capped at the speed you can plot data to the screen but you can alter your data set to display the most relevant information with less screen refreshes.