The MicroStation V8 DGN file format is a superset of both the MicroStation/J (v7) and DWG file formats.
Although prior versions of MicroStation performed all calculations in IEEE double precision floating point, many design coordinates were stored as 32-bit integers. In contrast, MicroStation V8 also stores design coordinates in double precision floating point.
The concept of establishing the DGN file coordinate system by defining master/sub/positional units is retained mainly because it makes the MicroStation V8 conversion process easier and it retains equity in seed files, references, etc. However, in MicroStation V8, there is a great deal of resolution between positional units. This makes DGN file setup considerably less important, because the accuracy in terms of master units is nearly unaffected by unit setup. The use of double precision floating coordinates also gives a design plane that is approximately 2 million times larger in each axis.
A MicroStation V8 DGN file is composed of one or more models. A model is a container for elements.
The MicroStation V8 DGN file format removes all file format-based constraints that were present in previous versions of MicroStation. Here are the specifics:
There is no limit on the number of levels per DGN file. Each level is named and stored as an element.
The maximum physical size of the DGN file is limited only by the operating system (the Windows NT limit is 4 GB).
The maximum size of a single element is 128 KB.
There is no limit on the maximum size of a cell.
Cell names are limited to approximately 500 characters.
There is no limit to the number of references that can be attached to a DGN file.
A line string, shape, or point curve can have up to 5000 vertices.
There is no limit to the number of components in a complex chain or complex shape.
There is no limit to the number of graphic groups in a DGN file.
The fence is parallel to the view in which it is placed.
A single line of text can contain 65,535 characters.
There is no limit on the maximum size of a text node.
There is no limit to the number of text nodes in a DGN file.
Each element has a unique 64-bit identifier that does not change through the life-cycle of the element.
Each element has a time stamp that indicates the time of the most recent change.