We occasionally have to share data with groups that use microstation, so we need to convert our Civil 3D drawings to .dgn format- including both AutoCAD linework and Civil 3D objects, such as points, alignments, profiles, etc.
There are a few ways to convert a Civil 3d dwg to a dgn.
Currently, the best way is to use the Export>DGN file tool. This can also be found in AutoCAD, but the tool within Civil 3D has been enhanced with the Subscription Advantage Pack to convert Civil 3D objects upon export (no need to explode).
If you are using Civil 3D 2010 and are on subscription, you should grab the Civil 3D Subscription Advantage Pack. Not sure how to get it? Read this post: How to Get the Subscription Advantage Pack for Civil 3D. The subscription advantage pack automatically enhances the tool that is already found under Export>DGN file- this is one that you don’t launch from the Toolbox.
The tool in its original form can also be found in AutoCAD Map 3D and AutoCAD.
When you launch the tool, it brings up a dialog where you can set up an export setup, specify a seed file and map layers to levels.
The resulting export will get all of your Civil 3D objects into the .dgn as a combination of blocks (cells) and linework. Even corridor objects get pushed out in 3D form. Note that this is your geometry- if you need your project data to go from Civil 3D to a Microstation based design package (such as InRoads or MXRoads) you’ll need to use LandXML or GENIO. There is a subscription extension for GENIO import/export, and a skillbuilder for help on using the Civil 3D GENIO tool.
Another way you can export drawings to microstation dgn is to use Mapexport. This is a tool that has been around for a few years and can be found in both AutoCAD Map 3D and AutoCAD Civil 3D.
While the tool still works, you will have to explode all of your Civil 3D objects twice before the export will handle them. Your best bet is to use the AutoCAD Export>DGN file with the Subscription Advantage Pack enhancements.
The Mapexport tool would be useful if you wanted to transform coordinate systems on export. For example, let’s say you were working with a drawing that was mostly mapping type data and a few Civil 3D alignments. You were working in State Plane Feet, but your friend using Microstation needed State Plane Meters, or UTM, etc. You could save a copy of your drawing, explode your alignments twice, then quickly do the export assigning the new coordinate system.