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now I try to automatize the creation of variable distance buffers for a line vector-layer with the help of the Graphic Modeler in QGIS. I don't want to save the buffer results as a new shapefile but instead adding the new features automatically to an existing shapefile (just adding not overwriting).

The problem thereby is that I can't specify the output in this way with the Graphical Modeler. Is there any possibilty to achieve this?

  • The grapical modeler can use only (but not all) the tools that are already within the program. If you can´t solve the problem with the availabe tools from the processing framework you have to work out some python code. It should work to append the new features using union. But you will have a new file and need to overwrite the old one. As the old one is loaded and therefore locked i´m not sure if this works. – Matte Jan 24 '18 at 12:47
  • There is a tool in the grapical modeler called v.edit that might do what you want. The description says: edits a vector map, allows adding, deleting and modifying selected vector features. – csk Jan 24 '18 at 17:08
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I had a similar problem in ArcGIS ModelBuilder, and the solution was to output a temporary result shapefile, load (add) the result in the right dataset then erase the temporary result shapefile.

I don't use QGIS graphic modeler but you may be able to do something similar.

  • Thank you! I know that this is a solution, but the modell I want to create should be able to add the new features directly to an existing shapefile. The tool should then be used by other users, which are not familiar with QGIS so I want to avoid any obstacles or possible error sources. – marc_mk Jan 24 '18 at 12:15
  • Yes but arcgis has the tool to load data or delete shapefile that you can add in a model, for the end user the operation are transparent and it seem that the result are directly added to the shapefile. If the same tool are not available for graphical modeler you could may try to ceate a script that do the same and add it to your model – J.R Jan 24 '18 at 12:35
  • Ah, now I got it! That would be a perfect solution, but I have't found yet such a possibility in QGIS and my skills are unfortunately not advanced enough to create such a PyQGIS script. – marc_mk Jan 24 '18 at 12:40

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