Handling MicroStation (DGN) Dimensions

Introduction

Dimensions are a type of MicroStation element (geometry). They are a form of annotation that depict measurements on a CAD drawing. Dimensions can either be linear or angular measurements:



FME can read dimensions and they can be created within an FME workspace by defining a series of FME format attributes. In this article, we will read in DGN dimensions.
 

Reading Dimensions

Dimension components are read into FME as a set of features. Open the Reader Parameters, expand the Advanced section of the Parameters. Here there is the option to “Drop Dimensions” this parameter controls whether the components of a dimension are split apart into separate features (dropped) or whether they will be retained as a group (aggregate) feature.

Find attached an example MicroStation dataset that includes dimensions. Read the dataset into the FME Data Inspector and notice the different format attributes used to define dimensions.
 

Round-Tripping Dimensions

To read dimensions with FME and then write them back to a new DGN dataset requires the dimension components to remain as an aggregate during the translation. If the option to drop the dimensions in FME is applied, the resulting DGN file will contain a series of separate line elements (right).

Dimensions Not Dropped Dimensions Dropped

Find attached an example FME workspace (template) that translates from DGN back to DGN, keeping the dimensions.
 

Writing Dimensions to DGN

Because of the complexity of dimensions, no single parameter exists on a DGN Writer that cause dimensions to be created. Instead, the user must define dimensions using a series of format attributes. For more information on how to do this, contact the FME support team.
 

Writing Dimensions to Other Formats

There is no specific definition for dimension features in the FME geometry model; therefore - like creating dimensions in DGN - writing DGN dimensions to another format requires the mapping of DGN format attributes to the format attributes of the other format.