Live scatter plot fetching data from firebase every 2 second

Question

I have a mobile application which does some calculation and throws x,y coordinates and are updated on firebase every 2 seconds.

Next i want those coordinates to be plotted on a floor plan live. For that i am using Scatter plot over the floor plan image. But i cannot make it live as soon as the data is fetched need help with that.

Here is the code till now:

import matplotlib.pyplot as plt
import numpy as np
import matplotlib.animation as animation

xs = []
ys = []
fig = plt.figure()
scat = plt.scatter(xs, ys, c='r', s=100)


def main():
    graph_data = open("testfile.txt","r").read()
    lines = graph_data.split("\n")


    for line in lines:
        if len(line)>1:
            x,y = line.split(",")
            xs.append(x)
            ys.append(y)

    plt.scatter(xs,ys)
    print(xs)
    print(ys)


ani = animation.FuncAnimation(fig,main(),fargs=(scat))
plt.show()

Getting error with animation.FuncAnimation TypeError: NoneType object argument after * must be an iterable, not PathCollection

Have updated the code, Just need help with the animation function, getting this error. `TypeError: update_plot() argument after * must be an iterable, not PathCollection` — Keyur Kariya, Mar 22 '19 at 07:22
The updating function needs to take an argument. `def main(i):`. The `FuncAnimation` needs to take this *function* as argument, not the return. `ani = animation.FuncAnimation(fig,main)`. This is to get rid of the error; the code will soon enough slow down, because you create a new scatter in each frame. Google for "matplotlib update scatter" for more efficient solutions. — ImportanceOfBeingErnest, Mar 22 '19 at 12:46

score 0 · Answer 1 · answered Mar 22 '19 at 08:41

You can fetch data in a separate thread while updating the plot in the main one. Here is a complete working example:

#!/usr/bin/env python3
import time

from queue import Queue
from threading import Thread, Event

import numpy as np
import matplotlib.pyplot as plt


FETCH_DELAY = 2


def fetch_data(queue, stop):

    while not stop.is_set():
        x, y = np.random.randn(2)
        queue.put((x, y))
        time.sleep(FETCH_DELAY)


def limits(array, offset=1):
    return array.min() - offset, array.max() + offset


def main():
    stop = Event()
    queue = Queue()

    worker = Thread(target=fetch_data, args=(queue, stop))
    worker.start()

    plt.ion()
    fig, ax = plt.subplots()
    plot = ax.scatter([], [])

    try:

        while True:
            data = queue.get()

            data = np.array(data)
            plt_data = plot.get_offsets()
            plt_data = np.vstack((plt_data, data))
            plot.set_offsets(plt_data)
            fig.canvas.draw()

            xmin, xmax = limits(plt_data[:, 0])
            ymin, ymax = limits(plt_data[:, 1])

            ax.set_xlim(xmin, xmax)
            ax.set_ylim(ymin, ymax)

            queue.task_done()

    except KeyboardInterrupt:
        pass
    finally:
        stop.set()
        worker.join()


if __name__ == '__main__':
    main()

Save it as plot_update.py file and run it from the command line:

python3 plot_update.py

Followed this Save it as `plot_update.py` file and run it from the command line: `python3 plot_update.py` shows no output — Keyur Kariya, Mar 22 '19 at 09:14
For me, it works like a charm: Ubuntu 16.04.6 LTS, Python 3.5.2. Any error messages? — constt, Mar 22 '19 at 09:41
No Error Message, and no output, i am using Mac Os Mojave, and Python 3.7 — Keyur Kariya, Mar 22 '19 at 09:55

score 0 · Accepted Answer · answered Apr 08 '19 at 10:33

Here is the solution without using threads it becomes very simple:

import matplotlib.pyplot as plt
import matplotlib.animation
import numpy as np
from firebase import firebase

firebase = firebase.FirebaseApplication('Firebase url', None)

fig, ax = plt.subplots()
x, y = [],[]
sc = ax.scatter(x,y,c=np.random.rand(3,))
plt.xlim(12,13)
plt.ylim(77,78)

def animate(i):
    xs = firebase.get('/Lat',None)
    ys = firebase.get('/Long',None)
    xs = round(xs,2)
    ys = round(ys,2)
    file = open("testfile.txt","a+")
    file.write("{0},{1} \n".format(xs,ys))
    file.close()
    graph_data = open("testfile.txt","r").read()
    lines = graph_data.split("\n")
    for line in lines:
        if len(line)>1:
            xs,ys = line.split(",")
            x.append(xs)
            y.append(ys)
            sc.set_offsets(np.c_[x,y])

ani = matplotlib.animation.FuncAnimation(fig, animate, 
                frames=2, interval=500, repeat=True) 
plt.show()

Live scatter plot fetching data from firebase every 2 second

2 Answers2