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Problem: Microstation v.8 DGN files are created with the unit 'international foot' by default

Description

Microstation® software, produced by Bentley Corporation, uses the international foot for data creation by default. The international foot is defined as exactly 0.3048 of a meter.

The U.S. survey foot, which is defined as 1200/3937 of a meter, is more commonly used in the United States.

Cause

The difference between the international foot and the U.S. survey foot is 6.0960121920e-7 m, or 0.0000006096012192 m.

This difference can become significant when multiplied by the False Easting or False Northing values used in the State Plane Coordinate System.

For example, the False Easting value in U.S. survey feet for NAD 1983 State Plane California Zone II (FIPS 0402) is 6561666.6667, while the value is 6561679.7900 in international feet. The difference between these two values is 13.1234. Data created in Microstation in this State Plane zone, with units of international feet, draws 13 feet west of where the data should be in relation to other data that is in U.S. survey feet.

Solution or Workaround

When a Microstation created Design File (DGN) is obtained from a source which created the file using units of 'feet', be sure that the source provides information about the units, i.e., whether the file was created with the international foot or the U.S. survey foot.

With this information, it is possible to define the coordinate system (projection) correctly for the DGN file and the data will align properly.

The link below provides documentation about the 'foot' definition used in Microstation version 8.

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