Topic: Create USFoot elevation surface from Metric DEM file

[sdunn]

Is there a way to do this on import?  The resultant surface from a normal import is translated, but the elevations are still in meters.

Does anyone have a utility that can convert the units of a DEM file externally?

[drizzt]

I am pretty sure you can tell map to take care of that for you upon import. I use DEM's often and I don't remember that being a problem. Let me take a look real quick

[drizzt]

Hmm.. I guess it is possilble I have always gotten DEM's with the elvations in feet and not meters. I know you can go here http://datagateway.nrcs.usda.gov/ and get NED's of anywhere in the US.

[Dent Cermak]

If I can do it directly in Carlson, you KNOW there has to be a way to do it in AutoCad. Keep looking. it's there somewhere, I bet'cha!!

[drizzt]

Ok, I had to test this to make sure before I gave you advise. If you have your drawing coordinate zone set up correctly for the area of your mapping / design, then when you create a surface from DEM, it will do the conversion for you. The DEM has its coordinate and units recorded in it, so Civil 3D just needs to do the math for you. It just needs to know where to start, thus, you need to have you units and coordinate zone set up.

If you still have problems i would like to test the DEM if you want to post it.

[sdunn]

Civil 3d will transform and scale the horizonal coordinates just fine.  The elevations are not being scaled to the drawing unit designation.  I have also tried setting the insunits variable to feet with no luck.

The ASCII DEM data is located here:

direct:
http://data.tnris.org/data/Elevation/DEM_3296.zip

site:
http://www.tnris.org/data-categories?type=quad&name=Addison&quicktabs_maps_data=1

I am importing the 30 meter file into a foot drawing with a zone setting of TX83-NCF.

[drizzt]

I'm going to give this a shot in Civil, if that doesn't work, I will convert to your zon with US foot both horizontal and vertical in GM.

[drizzt]

Looks like the dem is to big to post

[drizzt]

I am pretty sure that when I imported the dem, it came back with feet in elevation units. I am showing an elevation range from 70.16' to 266.16'. Do you know what the elvation range should be?

[drizzt]

Ok, my first import into Civil did pull in meters. It reads as feet, but looking at the elavations, it is actually meters. I used the transformation tab in the drawing settings and that didn't help. I do have the dem converted using GM, but I can't post it. Do you have a way for me to get it to you?

[mjfarrell]

I will be looking at this later today in Abu Dhabi, pardon the time delay.

[huiz]

Ok, my first import into Civil did pull in meters. It reads as feet, but looking at the elavations, it is actually meters. I used the transformation tab in the drawing settings and that didn't help. I do have the dem converted using GM, but I can't post it. Do you have a way for me to get it to you?

I have the same problem with DEM files which are set in centimeters, they are treated in C3D as meters. I'm not sure if that is a bug, if there is a solution or how I can solve this. Till now there is not much I can do with DEM files.

[sdunn]

drizzt, what tool did you use to scale the DEM elevations?  I am more interested in the method than getting the file converted.  This is not the only DEM file I am working with.  There are several work-a-rounds that I can do, but they are all convoluted and time consuming.  There are also a lot of crashes involved as most of the DEM files are pretty large.

[Cathy]

I think if you just create a grid surface, then add the DEM file to the surface, C3D is smart enough to do the conversion for you.  At least is was that smart in 2008. 

[Jeff_M]

Maybe I'm overlooking something since I don't use DEM's very often, but it appears there is pertinent data missing from these files.

[Jeff_M]

Actually, now that I look at the downloaded files more closely, it appears the data is there but C3D is not reading it (or not reading it correctly).

[Cathy]

And now that I have downloaded the files, I see that they are not USGS .dem files.  It appears to me that they are ArcGIS ASCII grid files.  You might try GDAL translate.  http://www.gdal.org/index.html 
I am still stuck in C3D 2008 -- not sure what version you are using, later versions may know how to read an ArcGIS ASCII grid file properly. 

[sdunn]

Actually, now that I look at the downloaded files more closely, it appears the data is there but C3D is not reading it (or not reading it correctly).

Jeff,
If you create a regular surface file, you can add DEM data.  The missing zone information for the DEM can then be entered correctly.  It will still not adjust the vertical though.

[mjfarrell]

I suggest new file from Metric template
new surface
insert the DEM data
Export to XML

New File from Imperial template
inport the XML file created above

[Novarese]

I suggest new file from Metric template
new surface
insert the DEM data
Export to XML
New File from Imperial template
inport the XML file created above

Brilliant, it works in my glorious Map2006.

I have no enough Ram to load http://data.tnris.org/data/Elevation/DEM_3296.zip so I tried with a small USGS dem (the Barringer crater in Arizona, UTM83 zone 12) surveyed in meters: check this out.

After your great tip, it appears like this in feet.

[sdunn]

I suggest new file from Metric template
new surface
insert the DEM data
Export to XML

New File from Imperial template
inport the XML file created above

This is what I am currently doing as a work-a-round. 

I was playing with the GDAL utilities as suggested by Cathy and using them you can convert the grid file to a SHP contour file.  This can then be used to create a surface as well.

[mjfarrell]

as far as I know the above is the only method that works correctly since C3D first appeared. (and in LDD)

[Cathy]

This is what I am currently doing as a work-a-round. 

I was playing with the GDAL utilities as suggested by Cathy and using them you can convert the grid file to a SHP contour file.  This can then be used to create a surface as well.

I would have used the GDAL utilities to create a USGS .dem file; I think it would be more accurate and C3D seems to know how to handle those properly

[drizzt]

drizzt, what tool did you use to scale the DEM elevations?  I am more interested in the method than getting the file converted.  This is not the only DEM file I am working with.  There are several work-a-rounds that I can do, but they are all convoluted and time consuming.  There are also a lot of crashes involved as most of the DEM files are pretty large.

I open with this http://www.bluemarblegeo.com/global-mapper/ then change the projection in global mapper and export dem, then inport into Civil

[Novarese]

then change the projection in global mapper and export dem

Are you really sure the resulting Dem is in feet..?

If I open the huge http://data.tnris.org/data/Elevation/DEM_3296.zip in Microdem, I get such an info:



You'd better check out your Dem from GM, sir...