I need to test if a vector layer, chosen by the user, is in geographic coordinates, according to the code below:

class RoadSlopeCalculatorAlgorithm(QgsProcessingAlgorithm):
    def initAlgorithm(self, config=None):
        self.addParameter(QgsProcessingParameterRasterLayer('MDT', 'Digital Elevation Model (DEM)', defaultValue=None))
        self.addParameter(QgsProcessingParameterFeatureSink('CalculatedRoadSlopes', 'Calculated road slopes', type=QgsProcessing.TypeVectorAnyGeometry, createByDefault=True, supportsAppend=True, defaultValue=None))
        self.addParameter(QgsProcessingParameterBoolean('VERBOSE_LOG', 'Verbose logging', optional=True, defaultValue=False))
        self.addParameter(QgsProcessingParameterVectorLayer('VectorLineLayer', 'Road network vector layer', types=[QgsProcessing.TypeVectorLine], defaultValue=None))
        self.addParameter(QgsProcessingParameterNumber('SegmentLength', 'Segment length (=> 5 times pixel size)', type=QgsProcessingParameterNumber.Double, maxValue=1.79769e+308, defaultValue=250))

    def processAlgorithm(self, parameters, context, model_feedback):
        # Use a multi-step feedback, so that individual child algorithm progress reports are adjusted for the
        # overall progress through the model
        feedback = QgsProcessingMultiStepFeedback(5, model_feedback)
        results = {}
        outputs = {}

        alg_params = {
            'INPUT': parameters['VectorLineLayer'],
            'LENGTH': parameters['SegmentLength'],
            'OUTPUT': QgsProcessing.TEMPORARY_OUTPUT

        # Check if vector line layer 'VectorLineLayer' is in geographic coordinates

        if alg_params['INPUT'].crs.isGeographic() :  #this is line 61 on the script
            # and so on .........

And there is the following error message:

*Traceback (most recent call last):
File "<string>", line 61, in processAlgorithm
AttributeError: 'str' object has no attribute 'crs'

How can I refer to the vector line layer object in [VectorLineLayer].crs.isGeographic()?

1 Answer 1


In your script, parameters['VectorLineLayer'] returns the layer's id which is a string. You need to use parameterAsVectorLayer to get the reference of the vector layer.

def processAlgorithm(self, parameters, context, model_feedback):

    # previous lines

    vector_layer = self.parameterAsVectorLayer(parameters, 'VectorLineLayer', context)

    if vector_layer.crs().isGeographic():
        # and so on

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