Arbitrary axis interval without affecting the plot

[parasonic]

Thank you for your replies. My task is to create a clone for the Matlab imagesc() which has one form where one can specify the axis extents in the arguments.

Would the following code theoretically change the x-axis to range from -100 to 20? As it is, the code here still allows the x-axis to be drawn from 0 to 127, and the plot shows up compressed and on the right hand side.

class RD_Qwt_Plot : public QwtPlotSpectrogram
{
public:
    RD_Qwt_Plot()
    {
        setItemAttribute(QwtPlotItem::AutoScale, false);
    }
 
    ~RD_Qwt_Plot()
    {
    }
 
    virtual void draw(QPainter* painter, const QwtScaleMap &xMap,
        const QwtScaleMap &yMap, const QRectF &canvasRect) const
    {
        QwtScaleMap cust_x_map;
        cust_x_map.setPaintInterval(xMap.p1(), xMap.p2());
        // Matrix spans 128 for the X direction
//        cust_x_map.setScaleInterval(0, 127);
        cust_x_map.setScaleInterval(-100, 20);
 
        QwtScaleMap cust_y_map;
        cust_y_map.setPaintInterval(yMap.p1(), yMap.p2());
        // Matrix spans 16384 for the Y direction
        cust_y_map.setScaleInterval(0, 16383);
 
        QwtPlotSpectrogram::draw(painter, cust_x_map, cust_y_map, canvasRect);
 
    }
 
/*
    // This method is referenced when checking to see what data to be plotted.
    // If you set the interval here, it changes both the axis and the
    // data plotted.
    QwtInterval interval(Qt::Axis axis) const
    {
        const QwtInterval interv(-34, 67);
        return interv;
    }
*/
};

class RD_Qwt_Plot : public QwtPlotSpectrogram
{
public:
    RD_Qwt_Plot()
    {
        setItemAttribute(QwtPlotItem::AutoScale, false);
    }

    ~RD_Qwt_Plot()
    {
    }

    virtual void draw(QPainter* painter, const QwtScaleMap &xMap,
        const QwtScaleMap &yMap, const QRectF &canvasRect) const
    {
        QwtScaleMap cust_x_map;
        cust_x_map.setPaintInterval(xMap.p1(), xMap.p2());
        // Matrix spans 128 for the X direction
//        cust_x_map.setScaleInterval(0, 127);
        cust_x_map.setScaleInterval(-100, 20);

        QwtScaleMap cust_y_map;
        cust_y_map.setPaintInterval(yMap.p1(), yMap.p2());
        // Matrix spans 16384 for the Y direction
        cust_y_map.setScaleInterval(0, 16383);

        QwtPlotSpectrogram::draw(painter, cust_x_map, cust_y_map, canvasRect);

    }

/*
    // This method is referenced when checking to see what data to be plotted.
    // If you set the interval here, it changes both the axis and the
    // data plotted.
    QwtInterval interval(Qt::Axis axis) const
    {
        const QwtInterval interv(-34, 67);
        return interv;
    }
*/
};

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Here is a screen shot of what currently happens.
cap.jpg

Thanks

[Uwe]

My task is to create a clone for the Matlab imagesc() which has one form where one can specify the axis extents in the arguments.

See QwtPlot::setAxisScale() and check the spectrogram example how to eliminate the margins. If you want to limit the area, where to display your spectrogram see QwtRasterData::setInterval().

What the heck is your motivation to manipulate the canvas maps ?

Uwe