qwtspectrogram axis adjustment for area not pixels - plot

Question

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 vector 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.

Answer 1

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