AutoCAD MicroStation DGN DWG Conversion

DWG → DGN
DGN → DWG

Trying to go back and forth from DGN to DWG will almost always cause problems. The two programs define some things differently and other things aren't common between them at all. Unless you started the original file with the goal to later convert it to the opposing format, and drew the entire drawing with that in mind, you will not likely meet with a perfect transition. Otherwise, unwanted elements that the other program can't assimilate will end up in the file, and these are what cause problems.

First, determine if the final destination for the drawing will be a DGN or a DWG. If it eventually has to go back to DWG again, I personally would start over from scratch. That's how big this can of worms might get.

The dwg should be converted according to its 'Z' information. In other words, if everything is on a zero elevation, you essentially have a 2D drawing and need to convert to a 2D DGN. Otherwise, it needs to be in 3D. Or, you could open a blank DGN and 'ref-in, copy, ref-out'. This means xref the original DWG file into the blank DGN. Draw a fence around it and copy the contents of the fence to some arbitrary location in your drawing. Then detach the reference file. Its elements that you copied are no longer reference elements, they are now part of your drawing (unlike AutoCAD which requires you to use the 'BIND' command to make an xref part of your DWG).

Before doing anything at all, however, you should clean the DWG to the greatest extent possible. Erase everything you don't need. Then, purge, audit, and purge again. Then purge/audit it again. Even if nothing is wrong with the drawing – some things can and will manifest as problems in a DGN environment even though they are functioning perfectly in ACAD. Get rid of every little thing that is not absolutely essential to the needs of the DGN. Text, shapes, even individual lines. Everything. If you don't need it in the DGN, erase it before you convert the file (Save a backup copy first!). Simply turning these layers off or freezing them is not enough.

Certain things can cause issues when moving from a DWG environment to DGN or vice-versa: anything custom, such as linetypes / linestyles, blocks / cells, using CTB's as your ACAD plot style, non-common fonts, wipeouts, reference files in the source file, layout tabs, and standards files.

There is a slight bug when converting DGN's to DWG's by saving as DWG in Microstation. The bug is with regular polylines. The polylines will not trim and refuse to be broken. To fix this, convert the polylines into LTpolylines.

Sometimes, AutoCAD will encounter a fatal error and the program will have to be aborted when trying to import DGN files.


System Differences

 

AutoCAD 2008

MicroStation V8

Layer/Level Unlimited named layers Unlimited numbered levels
Colour 255 colours - normally assigned by layer 255 colours - standard and user defined colour palettes - normally assigned by entity
Linestyle Standard supplied and User defined - normally assigned by layer - scales with plot scale or block scale 8 standard and user defined - normally assigned by entity - does not scale with plot scale or cell scale
Lineweight/Width/Weight Actual width - can be assigned to linear entities - scales with plot scale or block scale Relative thickness - can be assigned to all entities - does not scale with plot scale or cell scale.
Text Styles Standard supplied and user defined Standard supplied and user defined
Plotting Colour is normally used for selecting pen width Weight is normally used for selecting pen width
Xref / Reference file Rectangular clipping in paperspace - nested or overlay Irregular clipping with voids - overlay only
Paperspace Support paper view of files with multiple viewports to modelspace Not supported directly. Uses separate sheet file(.s01, etc.) with DGN attached for each viewport.