QGIS: use geometry from different layer in symbology expression

Question

I have a project with multiple layers. The purple dots are from a pointfile with the symbology-expression: z($geometry)> '14.5'. (so it only displays a purple dot when the Z-value is more than 14.5m).

I have a second layer with polygons, visible as the partly-transparent arc-area in red.

The next step i want to make in my project is to: have the purple dots appear only if: z($geometry)>'14.5' AND the x-y of that spot is within the geographical extent of the polygon from the second layer

What step do i have to take to get this done.

Answer 1

Your question is very similar to what I've done here recently.

I used expression:

if(
within($geometry,geometry(get_feature(layer,attribute,value))),
result_when_true,
result_when_false
)

In your case step 1: filter data table by

z($geometry)> '14.5'

step 2: paste expression in point symbology layer (see gif to find where)

if(
within($geometry,geometry(get_feature('your_polygon_layer_name','the_layers_field','feature_data'))),
1,
0
)

You can use the same expression for labels but must change 1 and 0 values to "label_field_name" and to null.

That's it.