How to create a convex hull using QGIS Geometry Generator?

Question

Background:

At 3.14.16, I'm trying to learn a little more about Geometry Generator, in this case convex hull. I created a simple test point layer with six points. I then used Geometry Generator with the expression convex_hull($geometry), expecting an outline hull to display. However, none appeared, as shown in the screenshot below. Only the original points appear.

In my search for a solution, I came across this SE GIS post, where convexHull($geometry) was successfully used. Unfortunately, that expression did not result in a outline for my points.

Question:

How do I display a convex hull around a point layer using Geometry Generator?

enter image description here

Answer 1

You need to select Polygon/ MultiPolygon geometry type for the geometry generator symbol layer, and add the collect function to your expression:

convex_hull(collect($geometry))

enter image description here

Update August 2023:

the $geometry function is now deprecated in favor of the @geometry variable.

So:

convex_hull(collect(@geometry))

• etrimaille: FYI, now, $geometry is deprecated. You should switch to @geometry instead
• Ben W: @etrimaille, thanks for the reminder- answer updated.

Answer 2

The correct answer is the one accepted.

Just adding another one if you are looking to do it with a common attribute :

convex_hull(collect (@geometry, group_by:="name_of_attribute"))

convex hull with a common attribute

A mix between Geometry generator - classify objects in QGIS and the accepted answer here

Just to share, it took me some time to see we could give a group by in the collect expression.