3

I'm trying to do a simple subtraction of 2 raster layers using QgsRasterCalculator in PyQGIS. I've searched around and thought I nailed it but the code below didn't yield anything, but there wasn't even a crash.

What could have gone wrong?

Each raster only contains one band.

target_ras_input = 'D:/Users/abc/Desktop/target.tif'
target_ras = QgsRasterLayer(target_ras_input,"target_raster")
QgsMapLayerRegistry.instance().addMapLayer(target_ras)

initial_ras_input = 'D:/Users/abc/Desktop/initial.tif'
initial_ras=QgsRasterLayer(initial_bathy_input,"initial_raster")
QgsMapLayerRegistry.instance().addMapLayer(initial_ras)

target=QgsRasterCalculatorEntry()
target.raster = target_ras
target.bandNumber = 1
target.ref = 'target_raster@1'

initial=QgsRasterCalculatorEntry()
initial.raster = initial_ras
initial.bandNumber = 1
initial.ref = 'initial_raster@1'

entries = [ target , initial ]

final_output = 'D:/Users/abc/Desktop/final_raster.tif' 
calc=QgsRasterCalculator ( 'target.ref - initial.ref', final_output , 'GTiff', target_ras.extent(), target_ras.width(), target_ras.height(), entries )
calc.processCalculation()

final_raster=QgsRasterLayer(final_output, "please_work")
QgsMapLayerRegistry.instance().addMapLayer(final_raster)
2

Like Joseph said, there is an error in the first parameter of QgsRasterCalculator. But it must be string, unlike Josephs suggestion. So i tried this:

calc=QgsRasterCalculator ('%s - %s'%(target.ref, initial.ref), final_output , \
                      'GTiff', target_ras.extent(), target_ras.width(), \
                      target_ras.height(), entries )

You'll want to correct that line, too:

initial_ras=QgsRasterLayer(initial_bathy_input,"initial_raster")

because initial_bathy_input does nor exist, so change it to

initial_ras=QgsRasterLayer(initial_ras_input,"initial_raster")
2

I think you need to replace the single quotes in

'target.ref - initial.ref' 

otherwise the expression is read as a string and does not reference the actual names you used.


So it should read:

calc=QgsRasterCalculator( target.ref + ' - ' + initial.ref, final_output , 'GTiff', target_ras.extent(), target_ras.width(), target_ras.height(), entries )

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.