I'm building a Python algorithm for QGIS 3, to be run from the Processing Toolbox. I've finished debugging the algorithm body, which seems to work, but QGIS is unable to load its output.
To summarize, the algorithm generates a vector layer in memory, sets up a QgsHeatmapRenderer object with some desired parameters, and sets this as the layer's renderer. It works correctly, but QGIS is somehow unable to deal with the result.
Here's the algorithm code (also available on GitHub):
# -*- coding: utf-8 -*-
# Create a heatmap of a single route, based on data from the OpenRouteService
# API. This is a proof-of-concept script only.
from PyQt5.QtCore import QCoreApplication
from PyQt5.QtGui import QColor
from qgis.core import *
import processing
import openrouteservice
# Define variables as necessary
# Here
failures = 0
# Create necessary functions
# Here
class MyProcessingAlgorithm(QgsProcessingAlgorithm):
"""
This algorithm creates a heatmap of a single route, based on data from the
OpenRouteService API. This is a proof-of-concept script only.
"""
# Constants used to refer to parameters and outputs. They will be
# used when calling the algorithm from another algorithm, or when
# calling from the QGIS console.
INPUT = 'INPUT'
OUTPUT = 'OUTPUT'
def tr(self, string):
"""
Returns a translatable string with the self.tr() function.
"""
return QCoreApplication.translate('Processing', string)
def createInstance(self):
return MyProcessingAlgorithm()
def name(self):
"""
Returns the algorithm name, used for identifying the algorithm. This
string should be fixed for the algorithm, and must not be localised.
The name should be unique within each provider. Names should contain
lowercase alphanumeric characters only and no spaces or other
formatting characters.
"""
return 'singlepathheatmap'
def displayName(self):
"""
Returns the translated algorithm name, which should be used for any
user-visible display of the algorithm name.
"""
return self.tr('Single Path Heatmap')
def group(self):
"""
Returns the name of the group this algorithm belongs to. This string
should be localised.
"""
return self.tr('Science Fair 2019')
def groupId(self):
"""
Returns the unique ID of the group this algorithm belongs to. This
string should be fixed for the algorithm, and must not be localised.
The group id should be unique within each provider. Group id should
contain lowercase alphanumeric characters only and no spaces or other
formatting characters.
"""
return 'sciencefairtwentynineteen'
def shortHelpString(self):
"""
Returns a localised short helper string for the algorithm. This string
should provide a basic description about what the algorithm does and the
parameters and outputs associated with it.
"""
return self.tr("This script creates a heatmap of a single route, \
based on data from the OpenRouteService API. This is \
a proof-of-concept script only.")
def initAlgorithm(self, config=None):
"""
Define the inputs and output of the algorithm, along with some other
properties.
"""
# Add a text input for the user's OpenRouteService API key.
self.addParameter(
QgsProcessingParameterString(
self.INPUT,
self.tr('Your OpenRouteService API Key')
)
)
# Add a feature sink in which to store our processed features (this
# usually takes the form of a newly created vector layer when the
# algorithm is run in QGIS).
self.addParameter(
QgsProcessingParameterFeatureSink(
self.OUTPUT,
self.tr('Heatmap Layer')
)
)
def processAlgorithm(self, parameters, context, feedback):
"""
Here is where the processing itself takes place.
This algorithm imports data from
"""
# Retrieve the API key and feature sink.
APIKey = self.parameterAsString(
parameters,
self.INPUT,
context
)
# And the description of the output layer (most likely 'memory:').
outName = self.parameterAsOutputLayer(
parameters,
self.OUTPUT,
context
)
feedback.setProgressText('Loading routes...')
# Begin processing
start = (-114.31506,48.20218)
end = (-114.63478,48.19400)
client = openrouteservice.Client(key=APIKey)
routes = client.directions((start,end))
encoded = routes['routes'][0]['geometry']
decoded = openrouteservice.convert.decode_polyline(encoded)
routeLayer = QgsVectorLayer("LineString", "Kalispell to Ashley Lake",
"memory")
provider = routeLayer.dataProvider()
feat = QgsFeature()
feat.setGeometry(QgsGeometry.fromPolyline(
[QgsPoint(pt[0],pt[1]) for pt in decoded['coordinates']]))
provider.addFeature(feat)
result = processing.run('qgis:densifygeometriesgivenaninterval', {
'INPUT':routeLayer,
'INTERVAL':0.001,
'OUTPUT':'memory:'
})
result2 = processing.run('native:extractvertices', {
'INPUT':result['OUTPUT'],
'OUTPUT':outName
})
# This is the output layer:
outLayer = result2['OUTPUT']
# Set up the desired heatmap renderer:
rndrr = QgsHeatmapRenderer()
rndrr.setColorRamp(QgsGradientColorRamp(
QColor('transparent'),QColor(227,26,28)))
rndrr.setRadiusUnit(1)
rndrr.setRadius(500)
# Set the output layer's renderer to the heatmap renderer just defined
outLayer.setRenderer(rndrr)
# Done with processing
feedback.pushInfo("Done with processing.")
# Return the output layer.
return {self.OUTPUT: outLayer.id()}
And the output from running the algorithm:
(The algorithm requires me to input my OpenRouteService API key, which I've blacked out in this screenshot.)
As you can see, the algorithm appears to have been successful, except for the final loading of results.
As instructed, I checked the Log Messages Panel's Processing tab, but it contains no indication of the error, only this:
Each entry here corresponds to a layer generated by the native QGIS Densify by Interval and Extract Vertices algorithms, which mine calls.
However, the Python Warning log tab does contain something interesting, albeit unhelpful:
I am relatively new to QGIS, so I'm unsure of what might be happening here. Can anyone offer some insight into this problem?
