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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.
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