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I am trying to create a polygon showing crown spread of a tree. Using QGIS.

I am aware you can achieve this with geometry generators, but I need to display symbols in legend and looking for a polygon creator so spatial analysis can be carried out in the future as well.

Does anyone know how to create a crown spread polygon or convert the geometry generator to a polygon?

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  • Depending on your data, you can create a polygon using the geometry generator. Which data is associated with your trees? Also, The polygon shape will be not visible in the legend. This function will be available only from QGIS 3.14 twitter.com/northroadgeo/status/1255085744835555328?s=20
    – Val P
    Apr 30, 2020 at 16:34
  • You only create a 'polygon' in terms of symbology with a geometry generator, I am wanting to actually create a polygon, either through a script or if there is a way to save the geometry generator symbology (so the polygon) as a shapefile/geopackage for example.
    – mh_perth
    Apr 30, 2020 at 16:42
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    mh_perth Any expression that creates a geometry using the Geometry generator can be also used in the Processing tool Geometry by expression to create a new layer with the new geometries.
    – Val P
    Apr 30, 2020 at 16:50

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As @Val P suggested if you want to create an actual polygon layer out of geometry generator you can plug the expression directly into Geometry by Expression.

If you need the layer to be dynamic (eg instantly show changes to the source data) but still show up as a polygon, then consider Virtual Layers - but you need to reformulate your expression to SQL. I have previously shared an example of such an SQL query here (pardon the strike through - maybe copy and paste to a text editor) I would advise against using a virtual layer with the geoprocessing tools if your data set is large though; better to do that with a static layer or write the processing into the virtual layer query itself.

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