Working units are the real-world units that you work with in drawing or creating your models in a DGN file. Typically the working units are defined in seed DGN files, from which you create your working DGN file. Normally, they will not require any adjustment.
You can choose master units and subunits by name, such as Feet and Inches, or Meters and Centimeters. Changing the working units Unit Names does not affect the size of geometry in your model. In summary:
- Working units are set as Master Units (the largest units in common use in a design, such as meters) and fractional Sub Units (the smallest convenient unit to use, such as centimeters or millimeters). Sub Units cannot be larger than Master Units.
- You can change your working units without affecting the size of elements in the design. That is, you can draw in Meters and Centimeters, for example, and then change the Unit Names to Feet and Inches to get the English measurements.
Format and Accuracy Settings
The Format and Accuracy settings control how coordinates, distances, and angles display in the status bar and dialogs.
Located in the Advanced Unit Settings dialog (opens when you click Edit in the Working Units section) is the Resolution setting, which determines the accuracy of the design plane and does affect the size of existing elements in a model. You should consult with your site administrator before changing the resolution setting.
In a DGN file, the Resolution setting is used to set the worst case accuracy for the design environment, which occurs only at the very edge of the (very large) working area. For example, working to a "worst case" accuracy of 0.0001 meters, the size of the design plane/cube is 900 million kilometers along each axis. Actual accuracy is many millions of times better when drawing near the origin of the design plane, which is the usual situation.
How Working Units Are Expressed
When you are inputting distances in DGN files, typically they are expressed in either of two forms:
- As a standard decimal number, such as 1.275.
- As two numbers separated by a colon, indicating " MU:SU." For example, "3:4" means three master units (MU), and four subunits (SU).
The following table has examples of distances expressed in the latter form.