Web Mapping Illustrated

Name

Microstation Design Files (DGN)

Synopsis

These are also known as DGN files.

File listing

Data is encapsulated in a single file, usually with the suffix .dgn; for example: 0824t.dgn.

Data access/connection method

• Access is available in MapServer through OGR.

• The CONNECTIONTYPE OGR parameter must be used.

• The path to the dgn file is required; file extension is needed.

• All types of features in a DGN file are held in one "layer" of data. The layer is called elements and is the first and only layer.

• The type of feature to be read from the DGN depends on the TYPE parameter in the map file.

• DGN files typically contain POINT, LINE, POLYGON, and ANNOTATION feature types.

• DGN files contain "styling" information, i.e., how to color and present the data. This is used, optionally, by specifying the STYLEITEM "AUTO" parameter.

  Warning

  DGN files typically use white as a color for their features and therefore aren't visible on maps with white backgrounds.

ogrinfo examples

Using ogrinfo on a single DGN file

Note that no geometry/feature type for the layer is identified because it can be multiple types.

                     > ogrinfo /data/dgn/0824t.dgn
    Had to open data source read-only.
    INFO: Open of '0842t.dgn'
    using driver 'DGN' successful.
    1: elements

Using ogrinfo to examine the structure of the file/layer

DGN files aren't really GIS data files. They evolved from drafting formats used by computer-aided drafting/design (CADD) programs.

They carry a few key attributes that are usually consistent across all DGN files. Most of the ...