Reading MicroStation (DGN) Tags with FME

Introduction

Tags are a MicroStation feature allowing users to attach non-spatial attribute information to DGN elements. To read this information as FME attributes, some specific parameters can be set in the reader. In this example, the element has two tags attached to it (Species and Tree Count): 

Step-by-Step Instructions

1. Add DGN Reader

Start FME Workbench. On the Start Page, select New Workspace to create a blank canvas. Add a Reader to the workspace (from the Readers menu, select Add Reader).

Set the Format to Bentley MicroStation Design (V8)

Set the Dataset to TreeTextNodeLabelsWithTags.dgn, which can be downloaded from the downloads section. Open the Parameters.

When adding a DGN reader to a workspace, the parameters dialog has an option, “Group Elements By”, that controls how DGN elements are grouped in FME Workbench. Select Schema - Level Names for Group By Elements. This will create an Attribute for each DGN Level.

Choosing any value of the "Schema" type will expose DGN tags as attributes in the FME workspace. When the reader is added to the canvas, more attributes are exposed than just the levels, such as igds_color.

2. Exposing Attributes
Notice that not only are the tags (here Species and Tree Count) exposed, but also attributes with information on the tags, such as the tagset name, the tag type, and the default value. If you need a list of tag names, you can expose the igds_tag_names{} format attribute by double-clicking on the Trees reader feature type. This will open the Feature Type parameters.. Click on the Format Attributes tab, find the attribute you wish to expose, and click the checkbox next to the attribute.

The tag attributes created within FME are defined using the same data types as in the original tags:

For example, a character tag in MicroStation will be created as an FME attribute with a character (string) data type; similarly, a numeric tag in MicroStation becomes a numeric attribute in FME. The width of the field depends on the attribute content.

3. Data Ready for Use
Now the information is available to use within FME Workbench, just like any other attributes, we can use an AttributeFilter to filter the trees by species name.

FME can only read tags with an associated value.

Data Attribution

The data used here originates from open data made available by the City of Vancouver, British Columbia. It contains information licensed under the Open Government License - Vancouver.