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Thread: QWT plot with autoscaling shows negative values in y-axis

  1. #1
    Join Date
    Nov 2016
    Qt products
    Unix/X11 Windows

    Default QWT plot with autoscaling shows negative values in y-axis


    I have a QWT plot which shows only positive data values as a curve. I want autoscaling to be done since the values are not fixed in a range. But when autoscaling is enabled for y-left axis, then y-axis starts with negative values. how can i avoid this?


    I tried changing void QwtPlot::updateAxes() in my own class but facing issues because of d_axisData[axisId] private data.


  2. #2
    Join Date
    Feb 2006
    Munich, Germany
    Thanked 871 Times in 819 Posts
    Qt products
    Qt3 Qt4 Qt/Embedded
    MacOS X Unix/X11 Windows

    Default Re: QWT plot with autoscaling shows negative values in y-axis

    Autoscaling means, that you want to calculate the scales from a given interval ( the bounding interval of all plot items having the QwtPlotItem::AutoScale flag enabled ). The algorithm for this calculation is implemented in the scale engine - usually QwtLinearScaleEngine::autoScale().

    If you are not happy with the result of the algorithm you have 2 options:

    • overload QwtLinearScaleEngine::autoScale
    • not using autoscaling and doing setAxisScale instead

    The code you would have to write is more or less the same.


  3. The following user says thank you to Uwe for this useful post:

    manikandan (1st December 2016)

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