The user can select a coordinate system for the Map view in the Setup tree view. The Map view coordinate system is selected using the drop-down menu labeled “Map view coordinate system”.
If the user would like for features of the model (i.e., branches, water users, catchments, etc.) to use a different coordinate system than the Map view coordinate system, then it is possible to select a different coordinate system using the drop-down menu labelled “Coordinate system for features stored in setup file”.
If two different coordinate systems are selected, the coordinates of the model features are automatically converted into the map coordinate system when displayed in the Map view. However, model features are saved in the model feature coordinate system.
In some cases, the coordinate system used for model features may be based on a different datum than the datum used in the Map view coordinate system. In these cases, a datum shift can be applied to locate model features correctly in the Map view. Two approaches are available: a three-parameter Molodensky transformation, and a seven-parameter 3D Helmert transformation. Details of the two approaches are documented in the geodesy manual supplied with the installation (MIKE_Zero_Geodesy.pdf).
See also: http://www.arcwebservices.com/arcwebonline/services/dattrans.htm.
A different coordinate system for model features should be considered if the study area is located in an area where distances are distorted significantly in the Map view coordinate system. For example, using a Sphere Mercator coordinate system in the north of Alaska would result in significant errors in calculated river reach lengths.
If the model working area is located in a region where the risk of significant errors due to distortion is large, the user will receive a validation warning. Validation messages will not be issued unless a working area has been defined.