Can anybody provide a hint on how to handle NULL values in QwtMatrixRasterData for QwtPlotSpectrogram based tool?
The NULL value that we've been using is -999999, but not clear on how to configure QwtLinearColorMap colorMaps so that the colorBar and final spectrogram image ignore these NULL values.

In the past, when working with random point data, I just ignored these NULLs at load time, and didn't have any problem creating the various colorMaps that we use.

Now that we are loading this data into a QwtMatrixRasterData object and need an nice ordered set of values, I need to account for every value, but I want to ignore NULLS in the final product.

I'd appreciate any help you can give.
Attached a screenshot of the image that includes these NULLS (see blue areas)Capture.jpg

Thank you