Thanks for your answer, I feared that this might be an option after all. I will try Rudi’s answer first and then yours. I will definitely post my insights here so everyone can profit
Frank
Von: Jean-Baptiste Desbas <jb.des...@gmail.com>
Gesendet: Freitag, 29. Juni 2018 16:03
An: Frank Broniewski <ha...@frankbroniewski.com>
Cc: Nyall Dawson <nyall.daw...@gmail.com>; qgis-user <qgis-user@lists.osgeo.org>
Betreff: Re: [Qgis-user] QGIS 3 Processing question
Hi,
I had the same issue. I had to loop over the output vector layer (child alg) to
feed the sink (main alg). Maybe is not the simpliest/shortest/fastest, but it
works.
Something like that :
o = processing.run(
'qgis:pointsalonglines',
params, context=context, feedback=feedback
)['OUTPUT']
(sink, dest_id) = self.parameterAsSink(
parameters,
self.OUTPUT,
context,
o.fields,
o.wkbType(),
o.sourceCrs()
)
for f in o.getFeatures()
sink.addFeature(f)
return {'OUTPUT':dest_id}
2018-06-29 9:35 GMT+02:00 Frank Broniewski <ha...@frankbroniewski.com
<mailto:ha...@frankbroniewski.com> >:
Hi Nyall,
thanks a ton for your response. I am well know for making things tricky for
myself 😃
Anyway, my testing-algorithm-script is still not working. It runs through, but
I do not get the expected result loaded into the layer tree. I suppose it runs
through - the output from the 'qgis:pointsalonglines' is a QgsVectorLayer -
but after finishing I get nuthink back.
Here's my complete script: You'll need a temporary polygon layer in a projected
CRS (I use EPSG:31466) for it to work nicely. Copy & Paste it into a new script
window and run it. I simply don't find the reason why the point result layer
isn't loaded into my layer tree ...
from qgis.PyQt.QtCore import QCoreApplication
from qgis.core import (QgsApplication,
QgsProcessing,
QgsFeatureSink,
QgsProcessingAlgorithm,
QgsProcessingParameterFeatureSource,
QgsProcessingParameterNumber,
QgsProcessingParameterFeatureSink)
import processing
class PolygonCenterline(QgsProcessingAlgorithm):
INPUT = 'INPUT'
DISTANCE = 'DISTANCE'
OUTPUT = 'OUTPUT'
def tr(self, text):
return QCoreApplication.translate('Processing', text)
def createInstance(self):
return PolygonCenterline()
def group(self):
return self.tr <http://self.tr> ('Cartography')
def groupId(self):
return 'cartography'
def name(self):
return 'polygoncenterline'
def displayName(self):
return self.tr <http://self.tr> ('Calculate a polygon centerline')
def initAlgorithm(self, config=None):
self.addParameter(
QgsProcessingParameterFeatureSource(
self.INPUT,
self.tr <http://self.tr> ('Vector Polygon Layer'),
[QgsProcessing.TypeVectorPolygon]
)
)
self.addParameter(
QgsProcessingParameterNumber(
self.DISTANCE,
self.tr <http://self.tr> ('Point distance value'),
type=QgsProcessingParameterNumber.Double,
minValue=10.0
)
)
self.addParameter(
QgsProcessingParameterFeatureSink(
self.OUTPUT,
self.tr <http://self.tr> ('Center line')
)
)
def processAlgorithm(self, parameters, context, feedback):
# qgis:pointsalonglines
params = {
'INPUT': parameters[self.INPUT],
'DISTANCE': parameters[self.DISTANCE],
'START_OFFSET': 0,
'END_OFFSET': 0,
'OUTPUT': 'memory:'
}
points = processing.run(
'qgis:pointsalonglines',
params, context=context, feedback=feedback
)['OUTPUT']
return {self.OUTPUT: points}
-----Ursprüngliche Nachricht-----
Von: Nyall Dawson <nyall.daw...@gmail.com <mailto:nyall.daw...@gmail.com> >
Gesendet: Freitag, 29. Juni 2018 01:04
An: Frank Broniewski <ha...@frankbroniewski.com
<mailto:ha...@frankbroniewski.com> >
Cc: qgis-user <qgis-user@lists.osgeo.org <mailto:qgis-user@lists.osgeo.org> >
Betreff: Re: [Qgis-user] QGIS 3 Processing question
On Fri, 29 Jun 2018 at 07:14, Frank Broniewski <ha...@frankbroniewski.com
<mailto:ha...@frankbroniewski.com> > wrote:
>
> def processAlgorithm(self, parameters, context, feedback):
You're making this tricky for yourself! Cut out everything in processAlgorithm
related to self.INPUT, and just pass the parameter value direct to the child
algorithm to handle:
> params = {
>
> 'INPUT': parameters[self.INPUT],
>
> 'DISTANCE': pt_value,
>
> 'START_OFFSET': 0,
>
> 'END_OFFSET': 0,
>
> 'OUTPUT': 'memory:'
>
> }
Nyall
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