You can export surface data to a DEM file and use the surface in other applications that support DEM data files. You can export all types of Autodesk Civil 3D surfaces, including terrain and volume surfaces.
Open a drawing with surfaces that you want to export to DEM.
Select a surface. Click Surface tabSurface Tools panelExport To DEMFind..
If more than one surface is available in the drawing, and you have not selected the surface in the previous step, in the drawing, click the surface which you want to export.
In the Export Surface to DEM dialog box, under Export, add information on the exported file, such as DEM file name, coordinate system, grid spacing, and elevation.
Specify if you’d like to use the default null elevation or specify a custom value and enter the value.
Click OK.
The surface data is imported to a DEM file in the location that you specified.
The exported DEM file inherits the coordinate zone assigned to the drawing. If the drawing does not have a coordinate zone assigned, you must specify one.