Working under QGIS 3.16.4 and using the Modeler, I would like to create buffers for a polygons layer.

The polygons layer includes the buffer size as an attribute (e.g. "BUFFER_M") resulting from the field calculator (a previous step in the model).

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Although I specified the polygons layer as the Input layer (Using algorithm output), there is no fields available (NULL) in the Expression Dialog.

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I tried to fix the Distance with the expected BUFFER_M field as following: Pre-calculated Value > "BUFFER_M" in the Expression Dialog with no success.

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All other steps in the model worked well but the buffers layer was generated with a Distance default value of 10,00 m.

Any ideas on how to specify the buffer size (Distance parameter) based on a field attribute of the input layer (vector layer)?

NB: the same problem when done manually as well (generated buffer of 10,00 m), however in this case the "BUFFER_M" field was available in the Expression Dialog.


1 Answer 1


Try the SAGA's Module 'Variable distance buffer'.

In the Buffer Distance field, please write the name of your field, that defines the buffer size.



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