[SOLVED] qwtspectrogram axis adjustment for area not pixels

habbas33

Hi I am using qwtspectrogram to plot my array data but the problem i am having is scaling.. the qwt scales are distributed over the intervals x and y and the axis are dependent on the pixels. for example if I have a data set of (500x500) and i want to plot for 500mm x500mm its perfect because it is translated over the pixels but if i want to plot 500x500 number of points for 300mmx300mm it is a mess and it shows in the plot 500x500 i know i have to manage the x and y axis but I have no idea how to do that. I manage to play a little and display 500x500 for 250mmx250mm area but can not do for others.
my code is as shown below

@class mydata: public QwtRasterData
{
    char filepath[35];
    QFile myfile;
    QVector<qint16> fileBuf;
    int pixel =500; // it represents the number of pixels in one row or column
    int dial =1000;
public:

mydata()
    {
    setInterval( Qt::XAxis, QwtInterval( 0, (pixel)-1 ) );
    setInterval( Qt::YAxis, QwtInterval( 0, (pixel)-1 ) );
    setInterval( Qt::ZAxis, QwtInterval( -dial, dial ) );

    {
     sprintf_s(filepath, "c:\\myfile.bin");
   
     myfile.setFileName(filepath);
     if(!myfile.open(QIODevice::ReadOnly)) return;

     QDataStream data(&myfile);
     data.setByteOrder(QDataStream::LittleEndian);

     while(!data.atEnd()) {
         qint16 x;
         data >> x;
         fileBuf.append(x);
     }

     myfile.close();
 }
}

virtual double value( double x, double y ) const//shifted
{
int x_pos = static_cast<int>(x);
int y_pos = static_cast<int>(y);
double c =  (fileBuf[ ((x_pos)+((pixel-(y_pos))*pixel))]);
return c;
}
}@

in short i have same number of pixels for different areas but i have same representation of axis in plot.

SGaist

Hi,

IIRC there was something like QwtScaleEngine or something for that part (but it's been a long time since I used these).

You should also try asking the Qwt guys

habbas33

hi, thanks for your reply. I manage to find the answer.

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;
    }
};@

include the following below code after creating a plot

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

this solved my problem

SGaist

Nice you found out and thanks for sharing !

Don't forget to update the thread title prepending [solved] so other forum users may know a solution has been found :)