How could I convert values of 32767 to 0 using raster calculator in QGIS?
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2Would you consider using GDAL_Calc? Do you want to change the values in the current raster or create an output raster with the values changed? – Michael Stimson Jan 8 '15 at 2:39
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Thanks, I will try :) I would like to have a new raster... – Nadia Jan 8 '15 at 23:10
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If you have SAGA installed you could use the raster calculator in QGIS processing (SAGA-> Grid - Calculus-> Raster calculator) with the formulae:
ifelse(a=32767, 0, a)
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I like that method, it gives the possibility of enforcing values other than 0, so it's more versatile, like for example anything greater than 255 to become 255: ifelse(a>255, 255, a). The Calc method only works for 0. – Michael Stimson Jan 11 '15 at 22:01
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Nadia, I have used GDAL_Calc (python script) to change one value (or a range of values) into 0. This can be achieved because False is 0 (True is 1) on the conditional statement. The calculation is Condition * Raster, where the condition is True the output is the raster value, where it is Falsethe value is 0.
Using the 3rd example:
gdal_calc.py -A input.tif --outfile=result.tif --calc="A*(A>0)" --NoDataValue=0
The conditional statement becomes:
gdal_calc.py -A input.tif --outfile=result.tif --calc="A*(A!=32767)"
Which is true wherever the raster is not equal (!=) to 32767.
answered Jan 11 '15 at 21:59
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If your raster layer name is RasterA, QGIS Raster Calculator expression is:
("RasterA@1" != 32767) * "Raster@1"
The logic has been clearly explained by @MichaelStimson, but just for clarity...
("RasterA@1" != 32767)is0if the cell value is32767.- Otherwise
("RasterA@1" != 32767)is1.
