Ok,
Ive managed to half get it working, but not very well. What I have had to do is copy the entire array into the SpectrogramData class, the use the data locally.
Qt Code: 
  1. class SpectrogramData: public QwtRasterData
  2. {
  3. public:
  4. 	QpnwPhasedArrayPlot * someParent;
  5. 	QVector< QList<double> > someData;
  6. 	// Provide pointer to QpnwPhasedArrayPlot so we can access the data
  7.     SpectrogramData( QpnwPhasedArrayPlot * theParent ):
  8.         QwtRasterData(QwtDoubleRect(0.0, 0.0, 180.0, 2000.0)) // Left, bottom, width, height
  9.     {
  10.     	someParent = theParent;
  11.     	someData = theParent->spectData;
  12.     	//QMessageBox::information(0,"","Creating Raster");
  13.     }
  14.     virtual QwtRasterData *copy() const
  15.     {
  16.         return new SpectrogramData(someParent);
  17.     }
  18.  
  19.     virtual QwtDoubleInterval range() const
  20.     {
  21.         return QwtDoubleInterval(0.0, 4096.0);
  22.     }
  23.  
  24.     virtual double value(double x, double y) const
  25.     {
  26.     	//QMessageBox::information(0,"","Real: " + QString::number(y) + " Round: " + QString::number((unsigned int)y));
  27.     	QList<double> temp;
  28.     	if( x < 0.0 || x > 180.0 || y < 0.0 || y > 2000.0 )
  29.     		return 0.0;
  30.     	else
  31.     	{
  32.     		return someData.at( (unsigned int)x ).at( (unsigned int)y );
  33.    		}
  34.     		//return someParent->spectData.at(1).at(1);
  35.     		//return 100;
  36.     }
  37. };
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I dont know what problems I will have in updating the data, hopefully replot() should take care of it for me, but I'm not sure.
There is surely a better way of doing this, where the SpectrogramData class can access some external data?