How to plot two real-time data in one single plot in PyQtGraph?

Question

I am willing to get 2 random data and plot it in the same Widget using PyQtGraph in a real-time way. I want them to show up as Red and Blue dots. However, after a hard time, my script does not work.

I would like to know what can I do in order to get both data in the same plot.

I know it is a silly question. I am a beginner in Python and coding.

Here is my code:

#-*- coding: utf-8 -*-
import random
import time
from collections import deque
import pyqtgraph as pg
from pyqtgraph.Qt import QtCore, QtGui
import numpy as np
import os
import spidev

win = pg.GraphicsWindow()
win.setWindowTitle('DOTS')


p1 = win.addPlot()
p1.setRange(yRange=[0,25])
p1.setRange(xRange=[0,25])
curve1 = p1.plot()


nsamples=300 #Number of lines for the data

dataRed= np.zeros((nsamples,2),float) #Matrix for the Red dots
dataBlue=np.zeros((nsamples,2),float) #Matrix for the Blue dots

def getData():
    global dataRed, dataBlue

    t0= random.uniform(1.6,20.5) #Acquiring Data
    d0= random.uniform(1.6,20.5) #Acquiring Data
    vec=(t0, d0)

    dataRed[:-1] = dataRed[1:]
    dataRed[-1]=np.array(vec)

    t0= random.uniform(1.6,20.5) #Acquiring Data
    d0= random.uniform(1.6,20.5) #Acquiring Data
    vec=(t0, d0)

    dataBlue[:-1] = dataBlue[1:]
    dataBlue[-1]=np.array(vec)


def plot():

    #Blue Dots
    curve1.setData(dataBlue, pen=None, symbol='o', symbolPen=None, symbolSize=4, symbolBrush=('b'))
    #Red Dots
    curve1.setData(dataRed, pen=None, symbol='o', symbolPen=None, symbolSize=4, symbolBrush=('r'))   


def update():

    getData()
    plot()

timer = pg.QtCore.QTimer()
timer.timeout.connect(update)
timer.start(50)

## Start Qt event loop unless running in interactive mode or using pyside.
if __name__ == '__main__':
    import sys
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        QtGui.QApplication.instance().exec_()# -*- coding: utf-8 -*-

I would really appreciate your help.

Answer 1

While pyqtgraph is a great package from a functionality perspective, unfortunately the documentation is lacking, and you really just have to dig in to the code and start to understand the structure of the objects.

When you call:

p1 = win.addPlot() 

This returns a reference to a PlotItem, at which point you can now add multiple PlotDataItems to this p1 object (see semi-useful structure diagram here : http://www.pyqtgraph.org/documentation/plotting.html#organization-of-plotting-classes )

So when you call:

curve1 = p1.plot()

This adds PlotDataItem #1, ... you now need to call it again to get a second reference to use:

curve2 = p1.plot()

This becomes PlotDataItem #2, which you can then use for the 2nd setData method in your plot() method to call during update(). Which would look like:

def plot():

    #Blue Dots
    curve1.setData(dataBlue, pen=None, symbol='o', symbolPen=None, symbolSize=4, symbolBrush=('b'))
    #Red Dots
    curve2.setData(dataRed, pen=None, symbol='o', symbolPen=None, symbolSize=4, symbolBrush=('r'))