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

  1. #1
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    Default QWT plot with autoscaling shows negative values in y-axis

    Hi,

    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?

    setAxisAutoScale(QwtPlot::yLeft,true);

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

    Thanks

  2. #2
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    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.

    Uwe

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

    manikandan (1st December 2016)

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