[Qgis-user] QGIS 3 Processing question

[Frank Broniewski]

Hi Rudi,

 

thanks a lot for your answer, I will definitely try that out. And once I’ve done it I will post my insights for future reference. I tried the QgsProcessingParameterVectorDestination already, but 

 

> Finally, in your `params` dict, change the value for OUTPUT from `memory:` to `output`

 

This is really new to me. Where did you find that? I really searched the docs up and down and gis.stackexchange as well, but never came across an output output for the output 😃

 

Many thanks,

Frank

 

Von: Rudi von Staden <rudivs at gmail.com> 
Gesendet: Sonntag, 1. Juli 2018 15:56
An: Frank Broniewski <hallo at frankbroniewski.com>
Cc: qgis-user <qgis-user at lists.osgeo.org>
Betreff: Re: [Qgis-user] QGIS 3 Processing question

 

Hi Frank,

 

On Fri, 29 Jun 2018 at 09:35, Frank Broniewski <hallo at frankbroniewski.com <mailto:hallo at frankbroniewski.com> > wrote:

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.

 

I had a similar problem. I think it's because the template defines the output as a feature sink, so you assume you have to use the same. I think if you change your definition from:

 

self.addParameter(

            QgsProcessingParameterFeatureSink(

                self.OUTPUT,

                 <http://self.tr/> self.tr('Center line')

            )

        )

 

to: 

self.addParameter(

            QgsProcessingParameterVectorDestination(

                self.OUTPUT,

                self.tr <http://self.tr> ('Center line')

            )

        )

 

and then in processAlgorithm you need to add output as a layer you can work with:

 

output = self.parameterAsOutputLayer(parameters,self.OUTPUT,context)

 

Finally, in your `params` dict, change the value for OUTPUT from `memory:` to `output`.

 

The new syntax is more complicated than it used to be, and it takes some time to wrap your head around it. I do find that it gets easier once you've got a couple of scripts under your belt.

 

Rudi

 

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