2011

When defining a custom datum, select the conversion technique, either
Molodensky, Bursa/Wolfe, or Seven Parameter Transformation. After choosing
the conversion technique, specify the appropriate conversion parameters for
the technique you chose.
See also:
■
Overview of Coordinate Systems (page 143)
■ Overview of Grid Data Files and Datum Shift Issues (page 103)
■ Defining an Ellipsoid (page 95)
To define a datum
1 Click Map Setup tab ➤ Coordinate System panel ➤ Define Global
Coordinate System.
Select Define or Modify.
2 On the General tab of the Define Global Coordinate System dialog box
or the Modify Global Coordinate System dialog box, select Geodetic.
Click Define.
3 In the Datum Manager dialog box, click Define.
4 On the General tab of the Define Datum dialog box, enter a code and
description for the datum (page 2059).
The code must be unique within a category and across all coordinate
systems and must not contain spaces. Only the following characters are
valid: A-Z (upper or lower case), 0-9, dash, and underscore.
AutoCAD Map 3D displays the description in the Datums list of the
Datum Manager dialog box.
5 Under Ellipsoid, select or define an ellipsoid (page 2062) to use for the new
datum.
For information about defining ellipsoids, see Defining an Ellipsoid (page
95).
6 On the Datum Conversion tab, select a conversion technique from the
Datum Conversion Technique list.
7 Enter the appropriate conversion parameters for the conversion technique
you selected.
Under Conversion Parameters, under Vector Component Deltas To
WGS-84 In Meters, enter the vector component deltas to WGS-84.
94 | Chapter 2 Setting Up