[gdal-dev] Amplitude virtual bands for complex datasets ?

[Michel Julien]

Dear Gdal developers,

I would like to discuss an idea that I think would be of great interest for those using Gdal to access complex dataset, such as SLC SAR products. Usually, when one want to visualize such data, looking at the real or imaginary part of the signal does not make much sense. People will compute amplitude, intensity, or even log-intensity and that is what they will look at (phase is to my best knowledge not very useful for visualization, but has a lot of value for processing).

Computing amplitude and phase from the complex value could be left to the end-user software, but :
- Most software do not provide such features (think of Qgis for instance, or MapServer),
- If overviews are generated from the real/imaginary image values with interpolation (nearest neighbor would be fine), then the generated overviews will be wrong, because you cannot interpolate complex data this way.

I think that Gdal could greatly ease the pain by exposing to the user virtual subdatasets corresponding to the amplitude, phase, intensity and log-intensity, for all complex datasets. In the case of multi-band complex datasets, those virtual subdatasets should also be multi-band, so that polarimetric data could be accessed directly as a multi-band amplitude image for instance.

>From what I know from Gdal capabilities this is not much work. I could try to do it myself, but I would like to get your feedback first (and some hints on where to start would be useful to me).

Regards,

Julien