_AeccFeatureElevsFromSurf not working for DEM

[Anonymous]

the tool is not working for a DEM i downloaded from TNRIS.  has anyone encountered this issue when working with a dem?  does the surface have to be in tin format?

[tcorey]

If Create Surface from DEM, you cannot get feature line elevations from the surface, but if you create a TIN surface and then add the DEM file as definition data, it does work.

I'm not sure why.

[RobertMansson]

I can confirm it works the same for me also:

- DEM-surfaces can't be used for _AeccFeatureElevsFromSurf (featurelines elevation from surface).

really bad.

[BrianHailey]

I've found that Civil 3D doesn't really like DEM data all that much. Typically DEM files are huge and cover a much larger area then needed and they tend to bog down Civil 3D quite a bit.

My recommendation would be to create the surface from the DEM file in InfraWorks (which handles huge data sets very well) and then import that into Civil 3d. When importing an InfraWorks model into Civil 3D, you can specify the area you want so you don't have all that extra data slowing down your drawing.

[RobertMansson]

Thanks for your reply Brian

In this specific case we are actually (for once) not complaining about Civil 3d's poor handeling of large amounts of data. We can also set a data-clip boundary on the DEM-surface in Civil 3d to reduce the amount of data in my surface.

The problem is the way Civil 3D favours TIN-surfaces over DEM-surfaces:

Other than "_AeccFeatureElevsFromSurf" not working for DEM-surfaces I can also mention that defining a surface by Definition>Edits>Paste surface doesn't work with DEM-surfaces, while pasting TIN-surfaces works fine.

Data references DEM-surfaces don't automatically synchronize upon loading a file, but TIN surfaces do.

[BrianHailey]

I've also seen issues when creating a surface from DEM where it doesn't correctly convert the elevations from meters to feet. InfraWorks just handles this really well. Drag the DEM file into InfraWorks, close it down, open the InfraWorks file in Civil 3D, choose the area of interest, boom you're done. And you have a TIN surface so you don't have to worry about the DEM surface issues.

But, as always, there's half a dozen ways to accomplish anything in CAD, finding what works best for you is the challenge.