QGIS point label expression - using a value from another layer

Question

I have a point data with depth values in CSV format as well as a polygon layer with a 'Critical_Depth' attribute. I'm trying to use the label rule expression to change the colour of the text depending on whether the point 'Depth' value is above or below the 'Critical_Depth' for that area.

I can achieve this by saving the CSV as a geopackage and adding a field 'Critical_Depth' that is calculated using a spatial join, but i'm wondering if i can simplify the process.

Above - Depths CSV data

Above - Polygons with Critical_Depth value

Above - Raw xyz data

Above - What I'm trying to achieve

Answer 1

I got it working with this - "Depth" > aggregate(layer:='DepthAreas',aggregate:='max',expression:="Critical_Depth",filter:=intersects( $geometry, geometry(@parent) ) )