Problem using processing.runandload(...)

Question

I'm writing a QGIS plugin using PyQGIS and I have a weird problem.

When executing following line of code:

processing.runandload("qgis:createpointsalonglines", r"Clipped", 1, 1, 0, r"memory:nodes")

Seems like Qgis doesnt allow me to output to a memory layer. The function works fine if I output to a an real (not-memory) layer, but I don't want that).

Why don't I want that? Beceause in that case, I have to create the layer first, and I need to have a path to save it..

The error:

enter image description here

However, with other processing.runandload functions (for example "qgis:clip"or qgis:orientedminimumboundingbox), it works fine with memory layer

For example,

I execute

processing.runandload("qgis:clip", "parallel", "polygon", r"memory:Clipped")

and

processing.runandload("qgis:orientedminimumboundingbox", "polygon", 1, r"memory:Oriented_MBBox")

without any problem, in the same program.

Anbybody has any idea why the problem occurs with the createpointsalonglines function?

The problem would also be solved if I outputed to a real layer. But in order to create a layer, you have to define the save path... But that doesnt seem like a good option, since I would then have to ask the user to give me a save path first.. Is there a way to create a layer somewhere without having to ask where? Maybe in the plugin folder? But how do I know the path to the plugin folder?

• Kristof de Werdt: Sorry! It did :)

Answer 1

You can use None as output parameter. Doing so, QGIS Processing creates a temporary vector file for you:

processing.runandload("qgis:createpointsalonglines", "Clipped" ,100,0,0,None)

Or:

res = processing.runalg("qgis:createpointsalonglines", "Clipped" ,100,0,0,None)
iface.addVectorLayer(res['output'],'my points','ogr')

In my case (on a GNU/Linux), the file is temporarily saved at:

/tmp/processing74861deb39ad40d2ad53cc9204ff2164/d2570e67f6444633824f27afbace50bd/output.shp