How to modify surface elevations from meters to feet (2024)

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

Solved by Pointdump. Go to Solution.

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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

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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

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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

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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

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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

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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

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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.

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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.

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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

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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

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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

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