Finding the nearest point with QGIS Field Calculator

Question

I have to point layers:

• Boreholes (with 100 features)
• Trees (with 300 features)

The tree layer has three attributes:

I would like to find the closest tree (based on "Tree_ID") to each borehole, using the Field Calculator. Traditionally, we use the "Distance Matrix" tool and set K = 1. I have done that, here is the result table:

However, I am wondering if this is possible using the Expression Engine in Field Calculator. I already have calculated the distance to the closest tree for each borehole using this expression:

aggregate(
    layer:= 'Trees', 
    aggregate:= 'minimum', 
    expression:= round(distance(@geometry, geometry(@parent)), 2)
    )

I created a new field for the boreholes, to show the distance to the nearest tree. Here is the result:

Now I would like to find out if I can use the Field Calculator expression engine to find the Tree_ID of the nearest tree. Is it possible to use the expression engine in the Field Calculator to get the ID of the closest tree?

Answer 1

I would recommend to use overlay-functions for that. They are faster then aggregate. With overlay_nearest you will get the nearest object in the target layer. Be aware that overlay functions return an array of objects. The following expression will return the nearest Tree_ID:

overlay_nearest(layer:='Trees',expression:="Tree_ID")[0]