How to identify spots where water pipe polylines get above the ground surface and add extra vertices with Z-coordinates to make sure the pipe stays at ~1 meter below the ground surface? I have a LAS of the ground surface and the polylines have Z valu

One way to do this:

Generate unique ids for lines. Counter or uuidgenerator.

Densify the lines to get more points. Densifier.

Chop the lines to points. Chopper.

Generate point order per line. Counter, group by line id.

Extract the z values to an attribute. Coordinateextractor.

Compare the points to the surface. Pointonrasteroverlayer or surfacedraper.

Extract the z values to another attribute. Cooordinateextractor.

Check original z vs surface z. Tester.

Correct point height when needed. 3DForcer or Vertexcreator.

Sort the points to get the original order. Sorter, line id, point number.

Rebuild lines from points. Linebuilder, group by line id.