AutoCAD Map 3D – Generating Contours from DEMs

AutoCAD Map 3D has a great function included that can generate contours from a DEM.   Simply right Clicking on a DEM layer in the Display Manger you will see a command to 'Create Contour layer’.  The resulting contour layer will be a new SDF file.

This command will bring up a dialog box that allows you to specify the parameters of the Contour Layer:  the Layer name for the Display Manager, the contour major and minor intervals, and the resulting SDF file location.

Once the Contours are generated, one would expect to be able to use the Data Table to view the individual contours and related data.  Well, one would be wrong…  as there seems to be an ‘undocumented feature’ (re: bug) where the data table does NOT display the contour data.

As you can see from this screen capture, only a single record is displayed in the Data Table.

To be able to see all of the contour records, you need to drill-down into the Feature Class and select the Contour Class:

Once you choose the Contour Class you will then see all of the records displayed in the Data Table:

*** NOTE ***
There is one caveat to this…  Even though you can ‘see’ the records, you can ‘zoom to a contour’ by selecting the record in the Data Table, or ‘zoom to the record’ by selecting a contour in the map.

Until next time,
Take care

Warren M

Comments

[Patrick Murphy]

Is it possible to export the contours to .shp files?

[Matthew Nashmi]

Yes, I recommend using the DWG MapImport and MapExport commands. With a right-click in the Display Manager you can export contours to an SDF or SQLite file. You can import the SDF or SQLite contours to DWG using MapImport and convert to SHP with MapExport. The contour elevations can remain as attributes.

[Nicholas Edwin]

The contours can eventually be converted to a shape file using different methods. The DEM to contour creation process actually creates an SDF layer. Which means it can be converted using several methods, the simplest as mention above might be to import into Map using the map import command then exporting as a shp file.

Hope this helps.

[Patrick Murphy]

Thanks, but something isn't working right. I have the dem and loaded it, then generated the contours. I right clicked the new contour layer and exported as sdf. The dem was about 9M and the sdf was only about 350k. When I import the sdf via Map>Tool>Import I only get about 3 horizontal lines but not the contours.

Note: when the dem is orginally generated these horizontal lines are there too.

[Patrick Murphy]

I deleted all of the previous sdf files and now it works ok. The output sdf was 57M. Thanks. This is a great aid to me.

Pat

[Frank Glatzel]

This method does create 2D contours, but how can I convert them into a 'proper' Civil 3D TIN surfaces. Is this possible from GeoTIFF files? It doesn't seem to work.

Ciao Frank