Revisions to using PyQGIS to subsample a region of a raster layer's pixel data

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edited Apr 13, 2017 at 12:34

1

There is a workaround using the processing.runalg() method, described in this post: Using in-memory vector layer with QGIS processing / SEXTANTE Using in-memory vector layer with QGIS processing / SEXTANTE.

EDIT: the script I copied was for vector clipping (not raster). I replaced it by GDAL's Clip raster by extent algorithm which does precisely what you want. You need to use the path to your raster as an input (and not the raster itself), though:

out_raster = processing.runalg("gdalogr:cliprasterbyextent", "path/to/raster.tif", "", "0,0,2,2", "", None)

There is a workaround using the processing.runalg() method, described in this post: Using in-memory vector layer with QGIS processing / SEXTANTE.

EDIT: the script I copied was for vector clipping (not raster). I replaced it by GDAL's Clip raster by extent algorithm which does precisely what you want. You need to use the path to your raster as an input (and not the raster itself), though:

out_raster = processing.runalg("gdalogr:cliprasterbyextent", "path/to/raster.tif", "", "0,0,2,2", "", None)

There is a workaround using the processing.runalg() method, described in this post: Using in-memory vector layer with QGIS processing / SEXTANTE.

EDIT: the script I copied was for vector clipping (not raster). I replaced it by GDAL's Clip raster by extent algorithm which does precisely what you want. You need to use the path to your raster as an input (and not the raster itself), though:

out_raster = processing.runalg("gdalogr:cliprasterbyextent", "path/to/raster.tif", "", "0,0,2,2", "", None)

corrected answer

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edited Apr 14, 2016 at 7:24

ArMoraer

5.7k
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There is a workaround using the processing.runalg() method, described in this post: Using in-memory vector layer with QGIS processing / SEXTANTE.

It seemsEDIT: the script I copied was for vector clipping (not raster). I replaced it by GDAL's Clip raster by extent algorithm which does precisely what you can do something like thiswant. You need to use the path to your raster as an input (it generates a temporary vector layer and calls QGIS' clipping functionand not the raster itself), though:

mem_layerout_raster = QgsVectorLayer("Polygon?crs=epsg:4326", "temp_layer", "memory")
if not mem_layerprocessing.isValidrunalg()"gdalogr: raise Exception("Failedcliprasterbyextent", "path/to create memory layer")            
mem_layer_provider = mem_layer/raster.dataProvider()

clip_polygon =tif", QgsFeature()
clip_polygon.setGeometry(QgsGeometry.fromRect("", QgsRectangle(0"0,0,2,2) ))
mem_layer_provider.addFeatures([clip_polygon])
mem_layer.updateExtents()

output = "output/path"
QgsMapLayerRegistry.instance().addMapLayer(mem_layer)
processing.runalg("qgis:clip", layers[0]2", mem_layer"", outputNone)

There is a workaround using the processing.runalg() method, described in this post: Using in-memory vector layer with QGIS processing / SEXTANTE.

It seems you can do something like this (it generates a temporary vector layer and calls QGIS' clipping function):

mem_layer = QgsVectorLayer("Polygon?crs=epsg:4326", "temp_layer", "memory")
if not mem_layer.isValid(): raise Exception("Failed to create memory layer")            
mem_layer_provider = mem_layer.dataProvider()

clip_polygon = QgsFeature()
clip_polygon.setGeometry(QgsGeometry.fromRect( QgsRectangle(0,0,2,2) ))
mem_layer_provider.addFeatures([clip_polygon])
mem_layer.updateExtents()

output = "output/path"
QgsMapLayerRegistry.instance().addMapLayer(mem_layer)
processing.runalg("qgis:clip", layers[0], mem_layer, output)

There is a workaround using the processing.runalg() method, described in this post: Using in-memory vector layer with QGIS processing / SEXTANTE.

EDIT: the script I copied was for vector clipping (not raster). I replaced it by GDAL's Clip raster by extent algorithm which does precisely what you want. You need to use the path to your raster as an input (and not the raster itself), though:

out_raster = processing.runalg("gdalogr:cliprasterbyextent", "path/to/raster.tif", "", "0,0,2,2", "", None)

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created Apr 13, 2016 at 19:04

ArMoraer

5.7k
2
26
49

There is a workaround using the processing.runalg() method, described in this post: Using in-memory vector layer with QGIS processing / SEXTANTE.

It seems you can do something like this (it generates a temporary vector layer and calls QGIS' clipping function):

mem_layer = QgsVectorLayer("Polygon?crs=epsg:4326", "temp_layer", "memory")
if not mem_layer.isValid(): raise Exception("Failed to create memory layer")            
mem_layer_provider = mem_layer.dataProvider()

clip_polygon = QgsFeature()
clip_polygon.setGeometry(QgsGeometry.fromRect( QgsRectangle(0,0,2,2) ))
mem_layer_provider.addFeatures([clip_polygon])
mem_layer.updateExtents()

output = "output/path"
QgsMapLayerRegistry.instance().addMapLayer(mem_layer)
processing.runalg("qgis:clip", layers[0], mem_layer, output)

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