[Qgis-user] (re)colloring overlapping parts of multipolygons

[Nicolas Cadieux]

Hi,
There are multiple ways of doing this.  The Join attributes by location (Summary) could help you could the number of polygons overlapping the point.  You could then split the overlapping  circles into smaller parts and then use the join by location again to transfer the sums polygon of the points back to the various circle parts.  Then use the symbology by classification using this field.

A much better way would be to make an interpolation of your point data instead. The easy way would be just to make a heat map.  The best way would probably be to use IDW with a search radius.  The gdal version of idw found in processing will permit you to do this.  Find an interpolation method that is compatible with the phenomenon you are studying. For example  IDW is would be better that a tin or a voronoï polygon.

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 19 juin 2021 à 10:54, Richard Duivenvoorde <rdmailings at duif.net> a écrit :
> 
> 
> 
> Hi List,
> 
> I'm experimenting to create 'flower'-shaped polygons for a point layer, denoting the signal coverage of several directional radio transmitters on a pole (fyi: to find/locate bats with small transmitters).
> 
> After some fiddling I came to the attached result for a point with 3 (but dynamic from attribute) transmitters using the following expression:
> 
> collect_geometries(
> array_foreach( string_to_array("azimuths"),
> make_circle( make_point(
>        $x + "bereik_m"/2 * cos(radians(@element)),
>        $y + "bereik_m"/2* sin(radians(@element))), "bereik_m" )
>        ))
> 
> The result being a multipolygon with overlapping parts.
> 
> In this work the overlapping area'a are (apparently) the most interesting, as there the 'location' accuracy is highest.
> 
> So my question: is there a way to give the overlapping area's really different colors.
> I've been playing with the layer rendering options, but ideally the area's in which there is no, 2 parts, 3 parts, and 4 parts overlapping should be differently colored..
> 
> I could try to create more advanced expressions (or probably I would go for some python) for that, but I was hoping maybe there is another trick/idea to use current multi-polygons, without adding 'parts'
> 
> Any help/tip is appreciated.
> 
> Regards & TIA,
> 
> Richard Duivenvoorde
> <multipolygon.jpeg>
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20210619/74c2a150/attachment.html>