Buffering by field value in the QGIS Processing Modeler

Question

I am using the processing modeler in QGIS 3.10. I want to buffer polygons with individual field attributes.

This is not a problem when I am not using the processing modeller since one can simply choose the respective attribute field from the loaded layers. However, when I want to automize the workflow in the processing modeler, I don't know how to tell QGIS from where it should take the attributes since there are no preloaded layers in the processing modeller (see picture attached).

I guess, I have to use the "Expression string builder", but I don't know which command I should use. Let's assume layer x contains the field y, which has the respective attribute values I want to use for buffering (which differ by polygon, so it's not a constant value).

How do I express that in the "Expression string builder", when using the processing modeler?

Answer 1

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

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

Answer 2

Instead of the "normal" Buffer-Tool, use variable distance buffer-Tool:

Add a Vector Field Input and change the input of the tool to Model Input. Then choose your field.

So your model looks something like this (simplified):

Answer 3

To Buffer by field value in the processing modeler in QGIS you have to set Distance to Value then click Edit and enter the field name (without quote or anything)

Answer 4

You can use Geometry By Expression:

buffer( geometry:=$geometry, distance:="distance1") Change distance1 to the name of your distance field.