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There are two rasters A and B. A is smaller but within B and since A has more up-to-date pixel values, I was able to merge A and B with "Mosaic raster layers" tool in QGIS which replaces B pixel values with A. However there is a problem, that A does have no value pixels (which are dummy high numbers e.g. -3.40282e+038), when the merge happens it overwrites the values of B with high noData values which I don't want it to happen as B has values for those missing points within A. Is there any way it could be done in QGIS? It should be possible with gdal_calc.py, but I don't know how to set up the rules.

I have tried the following so far, but i hope there is a one-step way of doing it:

  1. Clipped larger B to the extent of A (otherwise gdal_calc.py doesn't work for different dimensions)
  2. gdal_calc.py -A A.tif --NoDataValue=-3.40282e+038 -B B.tif --outfile=result.tif --calc="where(A==-3.40282e+038,B,A)"

After doing these steps i was planning to do mosaic of result.tif and B.tif, however result.tif is not correct, so I must be doing the where rule in gdal_calc.py incorrectly.

Rather than doing a lot of steps, there might be one tool which specifies "do not merge NoData of A" etc, but at the moment the merge product is coming back with -3.40282e+038, whereas original A raster didn't show up this value in symbology.

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