qwtspectrogram axis adjustment for area not pixels

[habbas33]

here is a class that converts double value of scale into string and display instead

class MyScaleDraw: public QwtScaleDraw
    {
    public:
        MyScaleDraw()
        {
            setTickLength( QwtScaleDiv::MajorTick, 10 );
            setTickLength( QwtScaleDiv::MinorTick, 2 );
            setTickLength( QwtScaleDiv::MediumTick, 0 );
 
            setLabelRotation( 0 );
            setLabelAlignment( Qt::AlignLeft | Qt::AlignVCenter );
 
            setSpacing( 10 );
        }
 
        virtual QwtText label( double value ) const
        {
            QwtText h=QwtText(QString::number(value*0.75); //use any scaling factor you want
            return h;
        }
    };

class MyScaleDraw: public QwtScaleDraw
    {
    public:
        MyScaleDraw()
        {
            setTickLength( QwtScaleDiv::MajorTick, 10 );
            setTickLength( QwtScaleDiv::MinorTick, 2 );
            setTickLength( QwtScaleDiv::MediumTick, 0 );
    
            setLabelRotation( 0 );
            setLabelAlignment( Qt::AlignLeft | Qt::AlignVCenter );
    
            setSpacing( 10 );
        }
    
        virtual QwtText label( double value ) const
        {
            QwtText h=QwtText(QString::number(value*0.75); //use any scaling factor you want
            return h;
        }
    };

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include the following below code after creating a plot

d_plot->setAxisScaleDraw( QwtPlot::xBottom, new MyScaleDraw() );
     d_plot->setAxisScaleDraw( QwtPlot::yLeft, new MyScaleDraw() );

d_plot->setAxisScaleDraw( QwtPlot::xBottom, new MyScaleDraw() );
     d_plot->setAxisScaleDraw( QwtPlot::yLeft, new MyScaleDraw() );

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this solved my problem

[Uwe]

I'm not 100% sure if I understand your initial mail exactly, but it looks like all you want to is to display a 500x500 matrix of values inside an area of a different size ( f.e 100x200 ) in plot coordinates :

rasterdata->setInterval( Qt::XAxis, QwtInterval( 0.0, 100 ) );
rasterdata->setInterval( Qt::YAxis, QwtInterval( 0.0, 200 ) );

rasterdata->setInterval( Qt::XAxis, QwtInterval( 0.0, 100 ) );
rasterdata->setInterval( Qt::YAxis, QwtInterval( 0.0, 200 ) );

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If you are using QwtMatrixRaterData this would be all, otherwise it might be a good idea to implement YourRasterData::pixelHint() returning the size of one data pixel.

With using your label transformation you are faking a different coordinate system to the user, than the one that is used by the plot. You will have effects, that the ticks are not aligned to your faked coordinate system, labels at other places ( picker/zoom ) might be wrong etc.

Uwe