How to modify surface elevations from meters to feet

[Anonymous]

Does anyone have a good workflow for creating Civil 3D surfaces from Lidar data in a different projection?  I'm downloading Lidar data from MnTOPO (http://arcgis.dnr.state.mn.us/maps/mntopo/) and want to use it to create Civil 3D sections.  The Lidar data is in UTM meters and my CAD drawing is in Minnesota state plane feet. 

I can create surfaces using the Lidar DEM files, but I'm having trouble re-projecting and converting the elevations from meters to feet.  I can re-project using ArcMap, but I don't have the spatial analyst to convert the elevations from meters to feet.  Exporting/importing LandXML files doesn't work and neither does this: https://forums.autodesk.com/t5/autocad-civil-3d-forum/converting-dem-surface-from-meters-to-feet/m-p....

How else can surface be re-projected and converted from meters to feet?

Thanks,

Scott

[Pointdump · Accepted solution]

Scott,

Don't use "Create Surface from DEM". Add the DEM to your Surface in Definitions. That will give you a Dialogue Box where you can set the DEM's Coordinate System. C3D is smart enough to convert those Metric Elevations to your Foot Surface. Try it.

Dave

[Anonymous]

Thanks Dave.  I swear I had tried that before, but for whatever reason, this last time it worked.  It's great that Civil 3D is spatially aware like that.  I appreciate your input.

Scott

[rmacan]

I just downloaded some NED 10m (1/3 arc-sec) DEM data from the USGS National Map service in an ArcGrid format.  When adding the DEM file as you suggest, it seems that C3D 2018 isn't reading the header info.  Iit should see it as LL83, but is assuming it's UTM Zone 0, and the units for elevation show as blank.   So it's not converting the elevs as it should and they are coming in as meters, but it displays them as though it's in feet (ie 1380' instead of 4528').  Is there a way to get C3D to read the header file info?  I don't recall having this issue before...maybe there is a better workaround I'm forgetting?

[Pointdump]

Randy,

Are you certain your data is in LL83? That's a Geographical Coordinate System, and the units are Degrees. Check the Metadata. Usually in the download there will be a Readme file.

Can you post a link to your data?

Dave

[rmacan]

Sure, here's the prj file info:
Projection GEOGRAPHIC
Datum NAD83
Zunits METERS
Units DD
Spheroid GRS1980
Xshift 0.0000000000
Yshift 0.0000000000
Parameters

This is the source for the data I am interested in. https://viewer.nationalmap.gov/basic/
Select Elevation Products, then 1/3 arc-second DEM, and try it on your end. I downloaded one from northern Arizona, of n36w112. It's near Leupp, AZ so you can zoom to it. If you would like me to send it to you, I can upload it to DropBox since it's close to 400Mb. Let me know.

Thanks!
Randy

[Pointdump]

Randy,

I downloaded that n36w112 adf easily enough, but I'm not able to bring it into C3D. My drawing is near-frozen with "Renumbering points and triangle indices..." Not much has changed in over almost 2 hours. I guess 115 million points is a pretty big file.
I haven't had much luck with creating C3D surfaces from data in lat-long coordinate systems. QGIS will open and style that big adf file in seconds, and you can use >>>GDAL-Translate<<< to kick out that file with elevations converted to Feet.

Dave

[Pointdump]

Randy,
"...it's not converting the elevs as it should and they are coming in as meters, but it displays them as though it's in feet..."
I added a Data Clip around Meteor Crater before importing that monster DEM. Getting the same as you. Other than GDAL Translate, I don't know how to fix it.
From Wiki-whatever:
"Meteor Crater lies at an elevation of about 5,710 ft (1,740 m)"

Dave

[Mike.M.Carlson]

Just a thought because I had to do this recently.  Import the DEM with a data clip into a default NCS meters.dwt set to the appropriate coordinate system.  Then check that it imported correctly.  Next export out a LandXML file of that surface and import into your standard usft .dwg.  C3D converts LandXML units from metric to imperial and vice versa efficiently.  I hope this helps.

[rmacan]

Hi Michael,

No that doesn't work for my purposes.  Basically, when I style it based on Slope %, the contour lines are showing when they shouldn't.  It's almost like the contour line is being created, and then merged into the slope styling somehow.  See my screenshot.  I created and exported the LandXML with no surface style, so not sure why the contours are even shown.  This didn't occur before when my elevations were wrong.

[rmacan]

Thanks Dave,

I looked at and attempted to add the units using GDAL Translate, but didn't see how to alter the units, but maybe I wasn't using it correctly.  It seems like a hassle to learn, and the online help seems like it skips steps, so what I have seen is hard to follow.  How would I change it to add the units as meters?

Thanks,

Randy

[Pointdump]

Randy,

In GDAL Translate, paste this in to convert Meters to Feet:
-scale 0 0.3048 0 1

I tried to do this in QGIS, but in version 3 and later you can't edit the GUI Command Window to add that scaling. So the only option I can see now is to use the old-fashioned, 40-year-old Command Line. Shoot me now. I haven't a clue where to even start there.

Mike's idea is interesting, but I haven't done much with XML-ing Surfaces.

Dave

[Pointdump]

Randy,
I converted that adf into a GeoTiff(UTM83-12) in QGIS by using "Save As". Took all of 10 seconds. Civil 3D was then easily able to transform from Metric UTM83-12 to Imperial UTM83-12F.

If you want to use GDAL Translate in QGIS, Grab version 2.18. It allows editing the Command Window where you can scale the elevations.

Dave