[Qgis-user] Request help 'Aggregate polygons' QGIS 3

[Harfoot A.J.]

Hi Flavio,

I'm not aware of a single tool that is the exact equivalent of the ArcGIS one.

The Concave hull (k-nearest neighbor) tool (part of the QGIS Processing toolbox, not a plugin) will generate the the bounding polygon, but does not allow input data to be grouped by a separation distance, but will accept a 'group' field which creates a polygon for each set of features having the same value for the field. This allows the separation distance to be incorporated:

  1.  Buffer the polygons by the maximum separation distance required, dissolving the results
  2.  Spatially join the original polygons to the buffer output so that each original polygon receives the unique id of the buffer polygon that it falls within
  3.  Create concave hulls using the buffer id field as the group field.

This sequence could be easily added to a model, simplifying and reducing the chances of errors when executing.

Andy


On 21/11/2019 17:46, flavio.taccaliti at libero.it<mailto:flavio.taccaliti at libero.it> wrote:
Hi everyone,

This is my first message in a users' group, I hope not to break any "netiquette" rule.

I have come across this little problem, and I would like to ask you if there is a simple solution to it:
I am looking for a QGIS 3 tool similar to ArcGIS "Aggregate polygons", http://desktop.arcgis.com/en/arcmap/10.3/tools/cartography-toolbox/aggregate-polygons.htm ( (it takes a multipolygon layer and aggregate the polygons that are closer than a given distance).

I have come across some results on the web, like using PostGIS (https://gis.stackexchange.com/questions/113084/qgis-equivalent-to-arcgis-aggregate-polygons) or
Unfortunately, I have no experience with Postgres or SQL yet, and given the limited amount of time I have for this task it would be unfeasible for me to learn them now.

"Concave hull" tool (https://plugins.qgis.org/plugins/concavehull/) does not what I am looking for, as I would like to set the maximum distance between polygons in the clusters, not the maximum number of polygons.
Also "aggregate" function seems to me not to aggregate polygons by their proximity (https://docs.qgis.org/testing/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#aggregate).

For the moment I have used the ArcGIS tool on another computer, but the idea is to write down some simple instructions for other users who will have even less expertise than me. Maybe the "button" already exists in QGIS 3, in that case excuse me for the repetition.

Thank you in advance for any suggestion or indication.

Best regards,

FT



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--
Andy Harfoot

GeoData Institute
University of Southampton
Southampton
SO17 1BJ

Tel:  +44 (0)23 8059 2719

www.geodata.soton.ac.uk<http://www.geodata.soton.ac.uk>
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