Civil 3D 2015 - Surface from DEM

[Lisa_Pohlmeyer]

I have recently been given a DEM file of our county. It's just under 2Gb in size. Is that too large?  I've looked at the help and there's no indication of that issue, basically instructions on how to create one.  Anyone else have experience using DEM files?  Limitations?  Suggested workflow?

[tcorey]

Civil 3D will choke on a DEM that size.

I would start a project in InfraWorks, set my project extents, attach the DEM, export to IMX, open Civil 3D, import IMX.

Tim

[Neilw_05]

You can skip the Infraworks step and just create a data clip boundary in Civil 3D as well. Of course you'll need to have an idea of the extents of the DEM and where you want to clip it to set the boundary.

There are several posts on the topic of creating surfaces from DEM's and it is also covered in the help system.

I recommend you NOT use the surface from DEM tool. Instead create an empty surface and then add the data from the DEM in the definition settings. That workflow gives you more control over the import settings (such as re-projection and datum transformations).

[Lisa_Pohlmeyer]

Neil,
I did exactly that in both the 2012 and 2015 versions, and neither of them worked. I created a surface and then created a data clip boundary, then added the DEM. couldn't get it to work in either version.

[Neilw_05]

What was the workflow you used? I've not had any problems with creating surfaces as long as the dataset doesn't overwhelm the software.

[Neilw_05]

Here is a small DEM that you can try. I know it works for me as I just tried it. Rename the file to .zip and expand it to a folder.

Create an empty surface then browse to and load the largest .adf file in the DEM folder to the surface definition under the DEM group. You should get a surface.

[Lisa_Pohlmeyer]

Neil,

Yep that works, and I have other larger *.adf files that work.  Do you have a file with a DEM extension that works?

My source file has a DEM extension and there's no other files with it.

[Neilw_05]

Here is a DEM that I just verified. It is an SDTS file so you'll need to extract it first. If you haven't worked with SDTS files before, you can learn how to extract them here: http://data.geocomm.com/sdts/

You will need a zip utility that can extract .gz and .tar files. 7zip is a free utility that will work. You will also need to download a SDTS to DEM translator. There are several links to translators on that site. I would post the extracted DEM but it is 10 MB.

PS; The forum filter won't accept the .gz filename so rename the attached file to .gz to extract it.

[c3dish]

That is a huge DEM. I have issues with 1 GB of contour data, so don't wonder if that is not that huge. You might need to resample it, or clip by grid in smaller DEMs. Do you need to build the surface for the whole county? If so, I would resample it, or export it to a different format and post process it outside with 3rd party tools. I am building an IFW model for like 1/4 of the city of Austin and the surface out of 2 foot contours is around 1.5 GB. With post processing I got to a good surface of only 100 MB using exported data to asc files. I would use post processing using either ArcGIS, Global Mapper and IFW to get you the best use out of that data. Otherwise, I guess you can tile the data in smaller chunks using like the USGS grid and then build the data using those.