How to make one terrain model that covers 2 or more unconnected areas

Question

When I import a DTM file that has several unconnected ditches in the same terrain model extra triangles are created to connect the areas. This gives incorrect volumes in quantity calculations. 
 The same happens when I try to create the terrain model from mesh elements. The best solution I can find is to use "Create terrain model from design meshes" this retains the element's boundaries but instead produces a terrain model for every single ditch area. This can end in 20 - 30 extra files. 
 Is it possible to make 1 terrain model that will cover all these ditch areas??

Openroads 2021 R1

caddcop · Accepted Answer

You can have multiple terrain models in a single DGN. In the past, you needed a DTM file for every separate surface. Now, if you have separate but related surfaces, they can all be stored in a single DGN file. But to prevent the connecting triangles, they must be separate terrain elements. This was sort of true in the days of DTM files. 
 You might be able to get it to not draw the long triangles, but one DTM could only have one exterior boundary and often, that was the only way to prevent other edge triangles from being formed.

Christopher Dalgleish · Answer

Hi Pete, thanks for the samples. The .XLSM attached works fine on the samples you shared, so should be able to scale up to suit. My initial suggestion of copying in the Surface node for each terrain into a single LandXML results in only one LandXML to import but multiple terrain models (which isn't what you want). In the .XLSM attached, populate the source path and click the orange button - that should combine multiple surfaces into one. The SourceData node is stripped out in the combined LandXML file, therefore ORD builds the terrain from the Definition only so it maintains the gaps across the terrain between input surfaces

LandXML utilities.xlsm

PEvans · Answer

Have you considered creating a complex terrain model that incorporates all the small terrain models so you only have one terrain model? You may have to add interior boundaries to prevent proposed triangles in unwanted areas. An exterior boundary may also be needed to achieve the desired results. 
 
 hth. 
 pevans

How to make one terrain model that covers 2 or more unconnected areas

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