# UNCLASSIFIED

Create Datum Dialog Box

The Create Datum dialog box has two tabs. The 3-Parameter tab is used to enter parameter information for datums that are specified using only three parameters. The 7-Parameter tab is used to enter parameter information for datums that are specified using seven parameters.

The 3-Parameter tab contains the following sub-elements:

- a Code field, in which you specify a new three- to six-letter code for the new user-defined datum. This code cannot be the same as any code that is already used for another datum.
- a Name field, in which you specify a name for the new user-defined datum. The name may be any string.
- an Ellipsoid pull-down list, with which you specify the ellipsoid that is to be associated with the new user-defined datum.
- Delta X, Delta Y, and Delta Z fields, in which you specify the datum shift values from the new user-defined datum to WGS 84. The shift values are optionally signed real values, in meters.
- Standard Error in X, Standard Error in Y, and Standard Error in Z fields, in which you specify the standard error for each of the datum shift values. The standard errors are positive real values, in meters. However, if the standard error is unknown, a value of negative one (-1) should be entered.
- a set of four fields in which you specify the valid domain of the new user-defined datum. The Western Longitude and Eastern Longitude values may be any valid longitude values. However, the Western Longitude value must be to the west of the Eastern Longitude value. The Northern Latitude and Southern Latitude values may be any valid latitude values. However, the Southern Latitude value must be to the south of the Northern Latitude value.

The Create Datum dialog box 7-Parameter tab contains the following sub-elements:

- a Code field, in which you specify a new three- to six-letter code for the new user-defined datum. This code cannot be the same as any code that is already used for another datum.
- a Name field, in which you specify a name for the new user-defined datum. The name may be any string.
- an Ellipsoid pull-down list, with which you specify the ellipsoid that is to be associated with the new user-defined datum.
- Delta X, Delta Y, and Delta Z fields, in which you specify the datum shift values from the new user-defined datum to WGS 84. The shift values are optionally signed real values, in meters.
- Rotation X, Rotation Y, and Rotation Z fields, in which you specify the datum rotation values from the new user-defined datum to WGS 84. The rotation values range from -60.0 to 60.0, in arc seconds.
- Scale field, in which you specify the scale difference value from the new user-defined datum to WGS 84. The scale value ranges from -0.001 to 0.001.

The Create Datum dialog box also contains the following sub-elements:

- a Cancel button – which aborts datum creation and returns you to the GEOTRANS main window.
- an OK button – which causes a new user-defined datum to be created using the specified parameter values.

# UNCLASSIFIED