I'm working in QGIS for a Digital Terrain Model.
I've got a table with point features, arguably vertices extracted from multipart iso-curves because the features are provided with a
"vertex_par" value along with an
"ID" (not unique, it recalls the original curve multipart feature ID).
Intent: I need to get the extremes of each original iso-curve lying on the property border into a table to feed my BIM-modeling app.
GOAL: I need to isolate all the points that are start and endpoints of the original curves (or parts).
Sketched in plain language:
For each group with the same "ID" value For each subgroup with same "vertex_par" I need to get the points with minimum/maximum "vertex_ind" value
QUESTION: How do I set an expression to filter these points?