PyQt, Qwt: Add a horizontal line (y=value)

[Lykanthropie]

Hi,

I am trying to plot a simple horizontal line in my QwtPlot. I have a plot with DateTimeScaleEngine (X-Axis) and a 'normal' y-axis with values 0-255.
How can I draw a horizontal line into this plot? This const. line will represent the mean value.

I don't want to fill the curve, just a line.

I tried f.e. this:

self.meanline = QwtPlotCurve()
self.meanline.setPen(QPen(Qt.green,2))
self.meanline.setStyle(QwtPlotCurve.NoCurve) 
self.meanline.setCurveType(QwtPlotCurve.Yfx)
self.meanline.attach(self.qwtPlot)

self.meanline = QwtPlotCurve()
self.meanline.setPen(QPen(Qt.green,2))
self.meanline.setStyle(QwtPlotCurve.NoCurve) 
self.meanline.setCurveType(QwtPlotCurve.Yfx)
self.meanline.attach(self.qwtPlot)

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All my tests failed!

Thanks!

[Uwe]

How can I draw a horizontal line into this plot?

When this line is across the complete canvas you can use a marker. If the line is for a specific interval you need QwtPlotIntervalCurve from Qwt 6, what is not supported by PyQwt.

You could also try to misuse QwtPlotCurve::Steps ( using curves with 2 points ). Otherwise you need to implement your own type of QwtPlotItem - what is more or less trivial for displaying a line.

Uwe

[Lykanthropie]

Thank you Uwe!

self.meanline = QwtPlotMarker()
self.meanline.setLineStyle(QwtPlotMarker.HLine)
self.meanline.setLinePen(QPen(Qt.green, 1))
self.meanline.attach(self.qwtPlot)
.....
self.meanline.setYValue(self.mean(numvalues))

self.meanline = QwtPlotMarker()
self.meanline.setLineStyle(QwtPlotMarker.HLine)
self.meanline.setLinePen(QPen(Qt.green, 1))
self.meanline.attach(self.qwtPlot)
.....
self.meanline.setYValue(self.mean(numvalues))

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It's working!