Surface From NED Files

Ok for all the Civil 3D and/or Land Desk Top users that have been asking on how to create a surface from the National Elevation Data (NED) files. Here is one way to create a C3D surface from of them. For those that are not aware the USGS site is now offering the NED format instead of the DEM from years ago.

First thing about this is when you download the files and unzip them is place the files in their own folder (directory) with a short path to them, do not unzip them to them same folder as other data or with a path a mile long, the shorter the better. Once you create the surface you can always go back and delete all the files anyways. I create a NED_Junk folder in my documents folder then clean house after I create my objects that I need. I used WinZip from the old DOS 5.1 days to unzip all the files into one folder, I notice using the windows zip app it unzips them into a two folders inside another folder.

In order to accomplish this task we need to use the Map 3D tools, so for you C3D users bring up the Map Task Pane, mapwspace at the command line. In the Display Manager, click on the Add Data icon to open up the data connect palette. In the Data Connect palette select the Raster Provider, use the file select icon and browse to the files you unzipped.

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The Data Connect Palette.

When you get to the folder that contains the NED files, set the display to show the details. Look at the largest file there and that is the one we need.

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The NED files.

The naming convention of them makes little to no sense so always find the largest one and use than. The rest of the files are used in “that other software” and MAP 3D can do with out them.

Once you selected the file Click the connect button on the Data Connect Palette. This will open another part of the palette and allow you to select the Schema to add to the map. In this case the schema is the file with the path.

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The Data Connect Palette with the Schema listed.

Select the schema (check mark in the box) then click the Add to Map button.

Now you should have something display in the drawing area like below.

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Don’t worry about how it looks or try to change the display of the features. All we need is for it to be part of the drawing (Map). You should also have some funny looking stuff in the Map’s Display Manager. For the non-map users this is called a map layer. The C3D toolspace is as confusing for Map users the same the Map Task Pane is to the C3D users. The thing we need to do is create an SDF file from the NED Raster. But it will be contours lines instead of a big blob. To do this in the Display Manager, right click on the NED layer and select Create Contour Layer.

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In the Generate Contour Dialog, provide a name for the contour layer. Set the contour elevation intervals, (you can type in any value), then select the units you want them in. Browse to where you want to place the new SDF file and provide it a name. Finally click OK.

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The Generate Contour Dialog.

The new SDF file and layer will be added to the map (drawing) and look like the below.

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The NED Raster and the SDF Contours.

You display may be different depending on the NED file and what you set the contour interval to. At this point we don’t care what it looks like we got our data we need in fact close out the drawing, don’t even save it. What data we want is the Contour SDF file it created, I hope you remember the save location you selected in the generate contours dialog.

Open up a new blank drawing. What we need to is use the mapimport command to import the contour sdf file to create polylines and create object data attached to them. From the map menu select Tools>Import, set the file type to SDF and browse to your contour sdf file. If you do not know how to import and create the object data the image below is a quick lesson.

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The Map Import of the SDF file and creating the Object Data.

Once you import the sdf file you will have polylines and object data attached to them, if you check the properties of one you notice it is at an elevation of “0” but the object data has the correct elevation listed. At this time save the drawing and close it out. We need to attach it to another new drawing and perform an alter-property query to alter the polylines elevation. So open a new drawing again and make sure the map task pane is open. Attach the saved drawing (the one you just saved and closed) using the map task pane. Now perform an alter-property query to set the polylines on their correct elevation. The image below is a refresher in accomplishing this if you need more “How-do” look here or here.

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Once you do the alter-property query you now have contour line you can use to build a surface from. Make sure you de-attach the drawing you attached to before you start so if you crash from to many contour lines it will be save and not end up getting a map drawing lock on the file. Then of course go back and clean out all those NED files you unzipped and any other files you may have created, the only one you need to hold on to is the original zip file and maybe the contour sdf file you created, the rest are trash.

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4 Responses to “Surface From NED Files”


  1. 1 gilan25 10/08/2008 at 1:05 PM

    The surface looks good!
    Everthing works fine up to saving SDF file. But I can not import the file again via File->Import because it asks for a SDF2/Sif file!
    Using Map->Tools->import I can not se the SDF option just SHP, tab, dgn etc.
    I am running MAP 3D.

  2. 2 bmapper 08/24/2008 at 8:54 PM

    Hmm. Still not seeing a difference. Im using Autodesk Map 3d 2008, if that helps. Everything is coming in perfect, except for the elevation units. Technically they are right, but in meters instead of feet. I guess my question is ‘How do i create contours from a NED DEM from the USGS seamless data website, and get them to show in feet?

    I hate to turn this into a question and answer forum, but after searching the net for hours for a solution, i dont know what else to do.

  3. 3 map3d 08/23/2008 at 5:09 PM

    Most likely the NED has the elevations in meters on the USGS site, while the x-y coordinates may be in feet the Z coordinates are still in meters. On the Map> Option dailog under the Current Drawing tab there is an option to adjust elevations.

  4. 4 bmapper 08/22/2008 at 4:40 PM

    Thanks for the tutorial. Its great. I’m having issues with the NED’s downloaded from the USGS ‘National Elevation Dataset’. When I go thru all the steps you mentioned above, and create the contours, the contours are coming in in meters, instead of feet, regardless of the units that I choose. So, instead of the elevation being 537.74, it says 170. Any thoughts to why this would be happening?


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