I am trying to make a simple plugin, from the input as a vector layer then processed with a Field Calculator function (But I want the ouput from this process to be saved in temporary memory or in other words the output to enter the next step function as an input) after that I want to do a Rasterized function.

I have tried to create the code :

def setVariables(self):

    self.rooftop = self.getRooftopLayer()
    self.rain = self.getRainfallLayer()
    self.potvol = self.dlg.le_potvol.text()

def Rasterize (self):

    alg_params = {
        'FIELD_LENGTH': 10,
        'FIELD_NAME': 'area',
        'FIELD_PRECISION': 3,
        'FIELD_TYPE': 1,
        'FORMULA': ' $area ',
        'INPUT': self.rooftop,
        'NEW_FIELD': True,
        'OUTPUT': QStringLiteral( "TEMPORARY_OUTPUT" )

    outputs ['FieldCalculator'] = processing.run('qgis:fieldcalculator', alg_params, feedback=feedback)

    if feedback.isCanceled():
        return {}

    alg_params = {
        'BURN': 0,
        'DATA_TYPE': 5,
        'EXTENT': outputs['FieldCalculator']['OUTPUT'],
        'FIELD': 'area',
        'HEIGHT': 30,
        'INIT': None,
        'INPUT': outputs['FieldCalculator']['OUTPUT'],
        'INVERT': False,
        'NODATA': 0,
        'OPTIONS': '',
        'UNITS': 0,
        'WIDTH': 30,
        'OUTPUT': self.potvol

    outputs['RasterizeVectorToRaster'] = processing.run('gdal:rasterize', alg_params, feedback=feedback)

def addLayers(self):

    self.iface.addRasterLayer(self.potvol, str.split(os.path.basename(self.potvol), ".")[0])

What statement I should add?

1 Answer 1


Add next lines. In your case you may want to add to def Rasterize(self):

def Rasterize(self):

    outputs = {} # ADD THIS LINE

    ### Your processing lines
    outputs['process1_name'] = processing.run(...)
    outputs['process2_name'] = processing.run(...)

    # Add next lines to the same scope/block with 'outputs[".."] =' and customize
    folder = "c:/ADD_A_FOLDER_PATH/" # remember last slash
    for k, v in outputs.items():
        mem_layer = v['OUTPUT']
        path = folder + k + ".shp" # k: process name
                                                "ESRI Shapefile")
  • Hi. I have tried but still shows an error #FieldCalculator Process processing.run ('qgis:fieldcalculator',...'OUTPUT': "TEMPORARY_OUTPUT" }) folder = "C:\Iqbal\Thesis Plugin\rwh_yield/" for k, v in outputs.items(): mem_layer = v['OUTPUT'] path = folder + k ['FieldCalculator']+ ".shp" QgsVectorFileWriter.. #Rasterized process using input from Field Calculator processing.run('gdal:rasterize',...'EXTENT': mem_layer,..'INPUT': mem_layer,...'OUTPUT': self.potvol }) It showed "NameError: name 'outputs' is not defined" Commented Dec 17, 2019 at 10:08
  • Use / (forward slash) (or \\ two back slahes) in path or add r before path. Please review this answer: stackoverflow.com/a/2953843/5569709 Commented Dec 17, 2019 at 10:13
  • The error refered to the "outputs is not defined in for k, v in outputs.items(): Commented Dec 17, 2019 at 10:13
  • Did you add outputs = {} line before using it? Commented Dec 17, 2019 at 10:17
  • ah yes! but now is coming another error: UnboundLocalError: local variable 'mem_layer' referenced before assignment Commented Dec 17, 2019 at 10:20

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