I have a Lidar .las file from an overpass. Im trying to get the basic outline from the top of the bridge to the road and the embutments. I would really like to have a cross section if thats possible. I have tried creating a surface but that only triangulates the space underneath the bridge which i need left open. I have also tried to create a DTM with the same result. This link shows what I would like to accomplish http://www.bentleyuser.dk/sites/default/files/e8_-_tunnel_design_with_inroads.pdf . I tried following the instructions but when importing dtm it says that triangulation is out of date. But if I triangulate i get bad results. Any help is appreciated, thanks