Comments on: Acquiring, Converting, and Using DEM Downloads in Civil 3D

By: Self Help Girl

Self Help Girl — Tue, 27 Jul 2010 15:12:19 +0000

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By: Kevin Harmon

Kevin Harmon — Thu, 10 Dec 2009 17:58:52 +0000

What do you do when Civil 3d does not allow you to change the CD Code of the DEM you are trying to import? I have been trying to import DEM files form the USGS Seamless server. Under ADD DEM FILE, [ - ] DEM file, there is no [...] button in the CS CODE line on the box. Clicking on the box does not produce a [...] box. Im stuck

By: Kevin Harmon

Kevin Harmon — Thu, 10 Dec 2009 17:58:00 +0000

By: Donnie Gladfelter

Donnie Gladfelter — Mon, 23 Mar 2009 14:29:22 +0000

@re-surfacing There are a number of variables that can play into the size of an imported DEM surface. As you note, generally your downloaded area is much larger than you truly need for a given project. Assuming you’re using Civil 3D 2009 I’d recommend 2 things. First, use the simplify surface command in C3D. This will remove unneeded points, thus reducing it’s overall file size. The second thing, 2009 introduces a new boundary type; data clip boundary.

Something to keep in mind with data clip boundaries is it must be the first item in the surfaces definition (eg. before the DEM file itself). If you forget to apply the boundary before importing the DEM, no worries. Just go to the surfaces properties, and move the data clip boundary to the top of the definition list (also something new to 2009).

By: Donnie Gladfelter

Donnie Gladfelter — Mon, 23 Mar 2009 14:29:00 +0000

By: Re-surfacing

Re-surfacing — Mon, 23 Mar 2009 14:18:29 +0000

I found the DEM files to be way to large to use as is. DWG file size gets huge (40+) mb, crashes a lot, won’t export to AutoCAD etc. To get a reasonable surface size after importing the DEM I had to draw a reasonable boundary, extract that smaller surface area, then create a new surface with the extracted surface in a new file.

By: Re-surfacing

Re-surfacing — Mon, 23 Mar 2009 14:18:00 +0000

By: Donnie Gladfelter

Donnie Gladfelter — Tue, 17 Mar 2009 16:16:54 +0000

@Earl – Thanks for the extra info! Being in Richmond, VA, Canadian DEM’s are especially something I’ve never encountered.

By: Donnie Gladfelter

Donnie Gladfelter — Tue, 17 Mar 2009 16:16:00 +0000

@Earl – Thanks for the extra info! Being in Richmond, VA, Canadian DEM’s are especially something I’ve never encountered.

By: Earl Kubaskie

Earl Kubaskie — Mon, 16 Mar 2009 01:43:43 +0000

Good post, Donnie.

Much of the USGS DEM data is also available in ESRI’s grid format, which C3D 2009-up can read directly.

I have also worked with a number of Canadian DEMs that are published in the original USGS format, requiring no conversion from SDTS. I’m not sure why the Desk doesn’t read SDTS directly, but much of the community hates SDTS anyway.

One thing you have to watch out for in any case (Canadians DEMs especially) is that the elevation values may be integers. C3D’s contouring and smoothing algorithms don’t really handle that situation well, resulting in a stairstep contour and a similar profile.