QwtPlotSpectrogram and contour lines

[toffkriss]

I did some further research. If I attach the QwtPlotSpectrogram I use to create the image to a regular QwtPlot, it turns out fine (see attached Image).
contourplot2.png
Seems to me, that the different origins of a QwtPlot and a QPixmap (or image in general) are not taken into consideration in the method QwtPlotSpectrogram::draw().

[Uwe]

Better try to understand, what the maps are about !

QPixmap plotImage = QPixmap(plotSize);
plotImage.fill(QColor(Qt::white));
QPainter painter(&plotImage);
 
QwtScaleMap xMap;
xMap.setPaintInterval(0, plotSize.width());
xMap.setScaleInterval(...);
 
QwtScaleMap yMap;
yMap.setPaintInterval(plotSize.height(), 0); // inverted !!!
yMap.setScaleInterval(...);
 
plotSpectogram.draw(&painter, xMap, yMap, QRect(QPoint(0, 0), plotSize));

QPixmap plotImage = QPixmap(plotSize);
plotImage.fill(QColor(Qt::white));
QPainter painter(&plotImage);

QwtScaleMap xMap;
xMap.setPaintInterval(0, plotSize.width());
xMap.setScaleInterval(...);

QwtScaleMap yMap;
yMap.setPaintInterval(plotSize.height(), 0); // inverted !!!
yMap.setScaleInterval(...);

plotSpectogram.draw(&painter, xMap, yMap, QRect(QPoint(0, 0), plotSize));

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Uwe

[toffkriss]

Thanks, that solved the problem.