Creating surface from .dgn contours

[Crass]

This is the first time I have imported a .dgn file into Civil. The drawing contains contours lines with Z elevation data. When I create a surface using this geometry (polylines + some lines) the surface seems to be scaled in the Z axis by 12.

For example pline (from dgn) is at elevation 46' but the Civil3D surface is 552'

I assume this is a setting in the Surfaces dialog box, but I cannot find it.

Also the elevation field in Properties from the dgn contours is weird. For example, in one area the (pline) contours display -28', 26', -24', -22', -20', -18' in Properties but Civil3D interprets this as a downward slope - which is the actual field conditions. I don't understand the conversion going on here.

The geometry of the pline and contours generated from the surface seem to line up in a side or isometric view (see attachment).

[Jay_B]

Sounds a lot like one drawing may be set a unit of Inches and the other set to Feet.
1'= 12".

[Neilw_05]

Look at the units of length reported in the properties dialogue on the left side of the screen cap. It is in feet and inches. That indicates your drawing units are not set to feet. You'll need to correct that before you import the DGN. Also make sure the units are set correctly in the DGN import settings.

If you want to post part of your dgn I'll take a look at it.

[Crass]

Thanks Neil. I figured it was something like that. Ideally the surface would be in decimal. When importing I tried both feet (unit) and inches (subunit) options in the dgn import dialog box. Also I had the dgn open in a new drawing rather than the current dwg. I assume this is using a template drawing where the units are engineering, and this is causing the problem. Do you think that is the case? If you want to take a look and try it, the file it is linked here: contours.zip. The file is 10mb, above the 5.2mb attachment limit.

I really appreciate it.

[_Hathaway]

I think the posters have identified the problem with the scale of 12. You will also want to be aware of the US Survey foot - vs International foot horizontal shift that 'may' affect your data.

Also, never create a surface from contours as it is a very poor way to create a surface. You may be aware of this but it is worth pointing out.

[Crass]

Thank you for the reply Mike. Unfortunately, contour data is all I have for this project at this point.

Can you elaborate on the "US Survey foot - vs International foot horizontal shift" or link me to a post or website that discusses this?

Much appreciated.

[Crass]

I was finally able to mess with this import again. The replies above seem to be correct. However, I doubt my solution is the preferred method of dealing with this issue. I simply imported the dgn, selected all geometry and scaled by 1/12. There must be a more sophisticated and accurate process.

I would think the "Conversion units" option in the Import DGN Settings dialog box would provide a way to fix this, but it seems to have no effect. I actually imported the model twice into the same drawing using both "Master units" and "Sub units" and the drawings came in at the exact same scale and location. I have tried changing the Insertion scale in the Drawing Units dialog box as well. This does not seem to have an effect either.

What am I missing?

Thanks

[Neilw_05]

You don't mention correcting your units in your C3D dwg. To eliminate any issues with your template, please try starting a new file with an unadulterated default C3D template.

If that does not correct the problem then the only other explanation I can think of is the DGN was created in inches.

[andrewpuller3811]

Just regarding the negative contour elevations, I encountered this same problem a few years back. I wasn't sure if it was due to the dgn or civil 3d import process. I had some 600 odd files to process so I wrote a vba routine to import the dgn and find any contours with bad values and correct them.

I do also recall that I found a few contours that had values that were +/- 0.05 from a whole number. Big pain.

[Crass]

Thanks for weighing in Andrew. it is very weird. All the contours behave as if they are negative (-x.xx from an unknown datum), but some are labeled with the - and some are not. Yet they seem to be in the correct location along the Z axis. In the photo below, the contour labeled 66.00 says elevation 66.00 in properties but actuallys exists at -66.00 in the dwg.