VRT Band Math algorithm

[Andreas Janz]

Since QGIS 3.22, the QGIS Raster calculator can store results as VRT. Unfortunately, this calculator can’t be used to execute Numpy / Python code.

The VRT Band Math algorithm should allow to do so, by using VRT Pixel Functions:
https://gdal.org/drivers/raster/vrt.html#using-derived-bands-with-pixel-functions-in-python

Compared to the existing, and more powerful Raster Math algorithm, VRT Band Math is limited due to some restrictions of VRT Pixel Function:

• each band is calculated individually
• inputs required for different bands may be read multiple times (maybe system IO caching helps)

Despite of the drawbacks, VRT Band Math can be very efficient for on-the-fly visualisation of indices like NDVI, EVI, Tessaled Cap, etc.

[Andreas Janz]

resolves #839

→ <<cset eebf9b927812>>

[Andreas Janz]

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