Export to DEM

[Anonymous]

Export to DEM Issues...

Anybody have any experience using the export to DEM functionality for surfaces?

My understanding is that it is supposed to use USGS dem format, but I'm having trouble getting the resulting dem to show up intact in ArcGis. The extents are off and it chopped off the northern half of the site...?

I think this is a Coordinate System issue, but can't figure out where I can change anything...

two screenshots attached. one shows surface in CAD, the other in GIS.

Thanks!

-d

[antoniovinci]

What happens if you load that .DEM back in Civil, how does it appear?

[Anonymous]

Hiya Antonio,

Thanks - I just tried that. Importing the DEM back into CAD does bring in the entire surface...

Hm. Any idea how well CAD has implemented the dem format? Maybe CAD can handle it, but arcGIS can't?

-d

[antoniovinci]

In your Civil may you export only to .DEM format, or others like .ASC or Geotiff ?

Seems like Arcgis can't decode well the .DEM one, so give a different try.

If it doesn't work, zip and attach it here, thx.

[Anonymous]

Oooohhhh  geoTiff.  I don't know what that is... but yes I can and it looks great when I pull it into GIS. Thanks Antonio!

[Anonymous]

So... the geotiff only kinda worked. I can view and manipulate the exported geotiff image in GIS (ArcGis 9.3.1) which is helpful.

However, see attached screen shot for error/warning message received.

My drawing is in CA state plane and my exported geotiff is also in Ca state plane so there shouldn't have been any transformation issues... thoughts?

Has anybody ever successfully created a dem or geotiff that ends up with a CS that GIS recognizes?

thanks

-d

[Anonymous]

Okay... get this. It works if I change the coordinate system of my drawing to CA state plane in meters (I was in feet earlier)...

Good to know... irritating, but as I've heard on this board before... there is always a work-around...

Hm.. I wonder if this fixes the originial issue I had with the export to dem command...

 -d

[Anonymous]

Still stuck on this. I can't get a dem (or a geoTiff) with the correct georeferencing.

so far the Export to DEM chops the surface weird (and produces weird errors in GIS) (My Original problem)

The geoTiff was promising.. but produces the error I linked to earlier.

If you change the CS in the dwg to State Plane meters, then GIS does not produce an error, BUT the surface is shifted (translated several meters to the west). screen shot attached shows original dem, and cad export.

This does not seem to be fixed even if I switch between survey feet or international feet . I've tried as many combinations of CS's, units, conversion factors, etc... to no avail... anybody?

Thanks!

-d

I checked all my surface definitions to make sure I didn't accidentally move the surface to the west at some point...nope! This shift is occuring for different projects with different surfaces...

[Anonymous]

I read through some of the older posts on this dem export issue... sems like this has been an issue since 2009!

Has anybody figured out how to get AutoCAD to export a correctly referenced and intact dem or geotiff surface?

-d

[Anonymous]

I'll figure this out yet...

The translational error depends on the distance from the origin. The attached images show two identical surfaces (as yellow borders) except that one is located near the origin and the other is way off to the northeast (coordinates of roughly 900,000,300,000 which are not unreasonable in a state plane coordinate system). With each surface I used the autocad command export to DEM and selected the geoTiff format. I then immediately created another surface from the exported gtif... Theses surfaces are shown as red borders. They are 'blocky' as you would expect with a DEM, but note the translational shift towards the origin... Is this a precision issue in CAD or a coordinate issue? projection issue? I could use some wisdom form the board on this.... I'm not sure where I need to look next for a solution to this...

thanks y'all.

-dale

[Neilw_05]

I experienced the same behaviors described in this thread. I submitted a support request and the behavior was confirmed.

After several exchanges with support the issue is being escalated. Here is the final reply I received:

I   am sorry that the DEM files created in Civil 3D do not work correctly when   importing to ESRI products. Having spent the better part of the last 12 years   relying on software to do my work, I know how frustrating it is when   something does not turn out as expected.
 
  So you are aware, I have been able to recreate in ArcGIS what you have   described. Meaning that no matter what grid size I export to DEM, it comes in   to GIS as a small piece of the surface. This held true all the way down to a   1' grid DEM. I was able to get the whole surface in and correctly located   with a 1' grid DEM. This means that the solution is to create a DEM with a 1'   grid spacing. Ideal or not, it does work, and gives you the desired results   inside ESRI. Note: When preparing to export the DEM, I do have to select   another Coordinate System because the USGS DEM file format does not support   the selected [assigned] Coordinate System. I select from the Projected list   NAD83/Arizona Central.
 
  All of that said, no matter what size I choose to create the grid, when I   import said DEM back in to Civil 3D, it comes in as the entire surface, and   is located correctly. When I bring in the DEM files to MAP, they also come in   as complete surfaces, even from 5' and larger grids. I even cut the surface   down into 3 rectangular shapes [thinking maybe the surface shape may be   causing some of the grief] and even the smaller pieces came in as partial,   except when created from a 1' grid. Why is the 1' grid working where the rest   do not when imported to GIS? That is impossible to say, because again, the   issue can only be recreated in an external program. Please see the attached   image. It is a screen capture of the 1' grid DEM described above imported   into GIS.
 
  From here the best I can do is escalate the case to the Development team.   They will then contact ESRI, and have to come up with a solution between   them. When an issue is escalated to our development team, they have to   perform their own research as to what might be causing the issue as well as   how to fix it. Their schedule is regulated by service pack and new release   timeframes, and the priority for fixing issues is determined by how the fix   impacts other functionality, and the business case for fixing the issue. Here   in Product Support, we are not informed of Development's schedule for fixing   issues such as this one.
 
  I have added the 1' DEM file I created from your surface data to the FTP. The   file is a little under 800mb. This will save you the time it takes to create   it from C3D. The FTP remains active for up to 30 days, but I would recommend   grabbing it sooner rather than later.
 
  Because there is a provided workaround, and this case is being escalated to   the Development team, all of the steps moving forward are out of my hands. I will be archiving the case now.

  
  CaseNo:08632231.

[Anonymous]

Don't know how helpful this post will be, considering that it's already been escalated up to the dev team, but I've never had any problems like this when exporting from C3D to ArcGis. I use the metric system all the time; maybe the issue is related with the use of feet? And like mentioned above, I also use the geotif format. I also have issues with the other formats that can be used.

[Anonymous]

I have been trying to solve this same riddle for quite some time.  I found a web page that provided an answer at http://thecadgeek.com/blog/2008/06/creating-a-dem-with-civil-3d/#comments  I proceeded though the steps until I get to the 1st bullet under step 3.  When I try to import the XML file back up pops a dialog box (see Attached).  I accept the default, since there doesn't seem to be anyway to edit it, and import the XML anyway.  When I measure distances from 2 identical locations between files I get the same number giving me the thought that I have not converted units at all. When all is done I am still unable to open in any independent USGS DEM viewers.  I have used 3rd party software to create TINs from XYZ points in a text file to eventually create a DEM that can be opened in the independent USGS DEM viewers but have sacrificed accuracy in the transformation.  To be able to go from C3d to a DEM usable outside of C3d would be the best.

[antoniovinci]

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doogie1959 wrote:

To be able to go from C3d to a DEM usable outside of C3d would be the best.

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What happens when you run the _SURFACEEXPORTTODEM command?

You should have both .DEM and Geotiff output: try 'em, then load in Microdem, for instance.