QwtRasterData and non-linearly sampled data

[Uwe]

This type of resampling works well if I am operating with linearly sampled data (XData and YData are equidistant.

One comment on your code: Spectrogram::value is called very often ( for each pixel ! ) and you should try to implement it as fast as possible. Better calculate dx and dy once instead of recalculating it again and again.

How can I improve this algorithm for a series of non-linearly scaled data (i.e. XData = [1 10 20 50 70 100 1000])?

Your code implements a nearest neighbor resampling. You can do the same for XData - beside the algorithm how to identify the next neighbor is different.

Again you should be aware of the fact, that Spectrogram::value is called very often and heavy calculations shouldn't be avoided if possible. F.e. you could overload QwtRasterData::initRaster() and QwtRasterData::discardRaster() to initialize some values, that are constant for the situation - or build a temporary linear value matrix.

Uwe