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 (500×500) and i want to plot for 500mm x500mm its perfect because it is translated over the pixels but if i want to plot 500×500 number of points for 300mmx300mm it is a mess and it shows in the plot 500×500 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 500×500 for 250mmx250mm area but can not do for others.
my code is as shown below

Qt Code: 
  1. class mydata: public QwtRasterData
  2.     {
  3.         char filepath[35];
  4.         QFile myfile;
  5.         QVector<qint16> fileBuf;
  6.         int pixel =500; // it represents the number of pixels in one row or column
  7.         int dial =1000;
  8.     public:
  9.  
  10.     mydata()
  11.         {
  12.         setInterval( Qt::XAxis, QwtInterval( 0, (pixel)-1 ) );
  13.         setInterval( Qt::YAxis, QwtInterval( 0, (pixel)-1 ) );
  14.         setInterval( Qt::ZAxis, QwtInterval( -dial, dial ) );
  15.  
  16.         {
  17.          sprintf_s(filepath, "c:\\myfile.bin");
  18.  
  19.          myfile.setFileName(filepath);
  20.          if(!myfile.open(QIODevice::ReadOnly)) return;
  21.  
  22.          QDataStream data(&myfile);
  23.          data.setByteOrder(QDataStream::LittleEndian);
  24.  
  25.          while(!data.atEnd()) {
  26.              qint16 x;
  27.              data >> x;
  28.              fileBuf.append(x);
  29.          }
  30.  
  31.          myfile.close();
  32.      }
  33.     }
  34.  
  35.     virtual double value( double x, double y ) const
  36.     {
  37.     int x_pos = static_cast<int>(x);
  38.     int y_pos = static_cast<int>(y);
  39.     double c =  (fileBuf[ ((x_pos)+((pixel-(y_pos))*pixel))]);
  40.     return c;
  41.     }
  42.     }
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in short i have same number of pixels for different areas but i have same representation of axis in plot.