How can i convert a 2d polyline shapefile into a 3d polyline based upon a dtm?

Hi,

One way to do it would involve the Surface draper or surface modeller.

Check out this exercise in our FME Desktop basic training manual.

It works with contours, etc - but the important part is right at the end where a building polygon is draped over a DTM to provide it with elevation. It uses the SurfaceModeller transformer.