Drawing an arc using pyqtgraph

Question

I need to draw some shapes on the screen using pyqtgraph. I chose pyqtgraph over matplotlib because the former is way faster when a lot of shapes are present. For lines polygons everything is ok, since I can simply plot multiple straight lines. But how can I represent efficiently an arc?

I found out here link that the function pyqtgraph.QtGui.QGraphicsEllipseItem() allows me to draw a full ellipse. But what if I just need an arc of that ellipse?

Answer 1

Here a solution where you can put two angles in degree and a direction for the arc (clockwise or counter clockwise). You can also put the radius. To translate the arc, you can just add two scalar for the x and y axis.

import pyqtgraph as pg
import numpy as np

from pyqtgraph.Qt import QtCore, QtGui

def Get_Points(r, a1, a2, nbPoints,clockwise=True):
    a1_rad = np.radians(a1)
    if a1_rad <0:
        a1_rad += 2 * np.pi
    a2_rad = np.radians(a2)
    if a2_rad <0:
        a2_rad += 2 * np.pi

    if a1_rad > a2_rad:
        if clockwise:
            t= np.linspace( a1_rad,a2_rad, nbPoints)
        else:
            t = np.linspace(a2_rad, a1_rad - 2 * np.pi,nbPoints)
    else:
        if clockwise:
            t= np.linspace(a2_rad, a1_rad,nbPoints)
        else:
            t = np.linspace(a1_rad, a2_rad - 2 * np.pi, nbPoints)
    x = r * np.cos(t)
    y = r * np.sin(t)
    return x, y

win = pg.GraphicsLayoutWidget(show=True, title="Plotting")
win.setFixedSize(500, 500)
p = win.addPlot(title='')
r = 10
a1 = 80
a2 = -200
x,y = Get_Points(r, a1, a2, 1000,clockwise=True)

c = pg.PlotCurveItem(x,y,cl=True)
p.setXRange(-1.5 * r, 1.5 * r, padding=0)
p.setYRange(-1.5 * r, 1.5 * r, padding=0)

p.addItem(c)

if __name__ == '__main__':
    import sys
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        QtGui.QApplication.instance().exec_()

Answer 2

You could compute the position of some points on the arc and display them with a PlotCurveItem

import pyqtgraph as pg
import numpy as np

from pyqtgraph.Qt import QtCore, QtGui

t= np.arange(0,5*2*np.pi/6 ,0.01)
x = np.sin(t+0.5)
y = np.cos(t+0.5)
win = pg.GraphicsLayoutWidget(show=True, title="Plotting")
win.setFixedSize(500, 500)
p = win.addPlot(title='')
p.setXRange(-1.5, 1.5, padding=0)
p.setYRange(-1.5, 1.5, padding=0)


c = pg.PlotCurveItem(x,y)

p.addItem(c)

if __name__ == '__main__':
    import sys
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        QtGui.QApplication.instance().exec_()