QGIS symbology geometry generator

Question

I´ve create a project now with a rule based symbology and there are problems with my geometry generator. I ´ve got two point layers "buffer" and "GNSS". Both with identical styles. There is a geometry generator script that place a point on intersection of nearest boundary. (white point)

collect_geometries(
array_foreach (
    overlay_nearest (
        @layer,
        boundary(make_circle($geometry, "Radius" )),
        limit:=9 -- max number of towers to consider
    ),
    Intersection (
        boundary(make_circle($geometry, "Radius" )),
        @element
    )
))

Now on my "buffer" layer all works fine, but in "GNSS" it shows me many white points? The script is from this forum, I don´t know where.

link to sample QGIS Job

---

I delete this geometry generator now, because of problems with vertex tool. I can´t move the point with vertex tool. It´s locked. When I delete the white intersection point (geometry generator), all works fine.

Answer 1

The overlay_nearest function is returning two points, itself and the other nearest one. See here: QGIS expression: when using overlay_nearest sometimes a feature considers itself its nearest neighbour

When the label from the post above is applied it shows the two fid's:

Both the second point and itself are returned from overlay_nearest. The boundary around the circle then intersects itself on one of the iterations causing the white points to appear around the outside. For this specific case, the expression can be changed to get the second element from the array.

collect_geometries(
    Intersection (
        boundary(make_circle($geometry, "Radius" )),
        array_get(
            overlay_nearest (
                @layer,
                boundary(make_circle($geometry, "Radius" )),
                limit:=9 -- max number of towers to consider
            ), 1 --get the second one
        ) 
    )
)

After the change:

Answer 2

overlay_nearest behaves badly when applied on the same layer, as it sometimes consider a geometry to be near itself, sometimes not.

When it does not consider itself as being near itself, the result of intersection is a (multi)point, and can be displayed as such (your working case).

However when it considers itself, then the result of the intersection is a (multi)line, and only the line is considered when styling it. That is, the intersection point between two different towers is lost.

As you have witnessed, this behaviour is not constant, so your style could magically start/stop working!

There are two alternatives:

1. work with polygons. Create the circle, then buffer them by a tiny bit and get the intersection. Style the output polygon as centroid fill. You might still get a dot at over the center point, so make sure to put this style below the style for the tower!

collect_geometries(
array_foreach (
    overlay_nearest (
        @layer,
        buffer(boundary(make_circle(@geometry, "Radius")),0.01),
        limit:=9 -- max number of towers to consider
    ),Intersection (
        buffer(boundary(make_circle(geometry(@feature), "Radius")),0.01),
        @element
    )
    ))

2. Alternatively, you can work on filtering the result so "self" is ignore. See this post for some options.