Change start / end points of a line with field attributes

Question

I've written an expression to update node layers coordinates to coordinate values from a survey file with the following expression:

geom_from_wkt('POINT('||$x||' '||$y||' '||$z||')')

(replacing $x, $y and $z with the field names of the northing, easting and elevation values) This works great for moving the nodes to the proper coordinates.

Now I'm trying to use the same logic to update the start and end points of a line layer but I can't seem to get the proper syntax, what I was expecting to work is:

geom_from_wkt('start_point('||$x||' '||$y||')')

geom_from_wkt('end_point('||$x||' '||$y||')')

(again, replacing $x and $y with the attribute field names)

I'm not getting any errors, but the geometry is also not updating... I can only assume the expression is not written correctly? or is there a better way to accomplish this task?

Answer 1

To update your line geometry, an expression like geom_from_wkt('Linestring('||"x1"||' '||"y1"||','||"x2"||' '||"y2"||')') should do it. In case you only want a point layer of start and end points to be updated use start_point(geom_from_wkt('Linestring('||"x1"||' '||"y1"||','||"x2"||' '||"y2"||')')) respecitvely end_point().

To get the attributes / geometry from your node layer to your line layer you need a matching field (id or similar) and use something like x(geometry(get_feature('yournodelayername','matchingfield_of_nodelayer',attribute($currentfeature,'matchingfield_of_linelayer')))))