Have you tried the 3dForcer?

Hi @maschlin,

I agree with @owen but have some additional pointers. First in the PointOnAreaOverlay make sure the Merge Attributes box is checked under the Attribute Accumulation parameters and leave the Accumulation Mode set to Merge Incoming. Then add a 3DForcer just to the Area output with the Elevation set to the Point _z value and Preserve Existing Z values to no.

Also I don't think you need the ElevationExtractor after your area features - but if you do either make sure this attribute has a different name than the point _elevation or make sure the Conflict Resolution parameter in the POAO is set to 'Use Incoming' so the features retain the point z values to be used in the 3DForcer rather than their own.

Thanks a lot! It all worked when checking the Merge Attributes box and with the 3dForcer

How do you set a Z value per vertex instead of keeping the same elevation for entire feature?

Use Chopper set By Vertex and Maximum Vertices to 1, connect it to a Counter so you can preserve the vertex order further down the workflow, PointOnPointOverlayer set to Merge Attributes where you merge the vertices on your feature with the points containing the Z value in an attribute, DuplicateFilter to keep only unique points based on the count key attribute, 3DForcer to put the attribute value from the features you overlayed to elevation, Sorter by count to bring the vertices in the original order (just in case they randomized themselves) and, finaly, LineBuilder to recreate your line.

Using this method you can transform the yellow-ish feature to the magenta feature: