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I'm working on a plugin for QGIS3, and trying to clip a raster layer using a vector mask layer. I've been able to successfully do this using "Clip raster by mask layer" through the processing toolbox, but when I use the following code in PyQGIS, it does not generate any output. I tried saving the output to 'memory:', to 'TEMPORARY_OUTPUT' and to a specific path in the disk, however, same result for all. Any tips?

from qgis.core import *
import processing

#load layers
project = QgsProject.instance()
mask = project.mapLayersByName('vector')[0]
input = project.mapLayersByName('raster')[0]

parameters = {
    'ALPHA_BAND': False,
    'CROP_TO_CUTLINE': True,
    'DATA_TYPE': 0,
    'INPUT': input,
    'KEEP_RESOLUTION': True,
    'MASK': mask,
    'MULTITHREADING': False,
    'OUTPUT': 'memory:',
    'SOURCE_CRS': dem.crs(),
    'TARGET_CRS': dem.crs(),
    'NO_DATA': -9999
}

clip_output = processing.run("gdal:cliprasterbymasklayer", parameters)

result = QgsRasterLayer(clip_output['OUTPUT'], "clipped", 'gdal')

project.addMapLayer(result)
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1 Answer 1

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You have to include 'OUTPUT' : 'TEMPORARY_OUTPUT' in parameters.

parameters = {
    'ALPHA_BAND': False,
    'CROP_TO_CUTLINE': True,
    'DATA_TYPE': 0,
    'INPUT': input,
    'KEEP_RESOLUTION': True,
    'MASK': mask,
    'MULTITHREADING': False,
    'OUTPUT': 'memory:',
    'SOURCE_CRS': mask.crs(),
    'TARGET_CRS': mask.crs(),
    'NO_DATA': -9999,
    'OUTPUT' : 'TEMPORARY_OUTPUT',
}

After that, it worked for me with my own example; as it can be observed in following image.

enter image description here

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  • You are right, it only works with 'TEMPORARY OUTPUT' as the algorithm output. However, I had already tried and it didn't work. Consequently, your answer forced me to check why it was working in your example and not in mine. I found the problem, the extent of the vector was larger than the raster's extensions. I seems than gdal simply returns nothing when it happens, without a warning. So, thank you!
    – Josep Pueyo
    Commented Jul 25, 2021 at 19:30
  • In addition, in your example, the 'OUTPUT' key in parameters is duplicated. It's better not have duplicated keys in a dictionary since it can lead to unexpected behaviour. The script works if you only left the 'OUTPUT' as 'TEMPORARY_OUTPUT' as you said.
    – Josep Pueyo
    Commented Jul 25, 2021 at 19:35

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