Hi
There is an huge bugg whithin xml surface model import.
Example files:
Tunnel in dxf referens (or import, the same result)
The same information in surface xml and imported to microstation is not good (bugg)
Lok at the sides of the tunnel in image, these are totally wrong.
Microstaion version:
Version:10.17.01.58
Tunnel is not DTM it is a mesh model. Terrain models(DTM or DEM) uses Delaunay triangulation generated from vertical view so if two points are sharing same XY coordinate but different Z then one of points will be ignored. It suits representing ground surfaces well except vertical or negative angled walls.LandXML is not suitable for this kind of data. You could try IFC or OBJ formats for data delivery.