You can create geodetic transformations from scratch, or by duplicating and editing one of the transformations in the Coordinate System Library.
To define a geodetic transformation
To modify an existing transformation, click Select and click the transformation in the list that displays.
These entries are for your convenience. The code will be used in lists of geodetic transformations, and the description can help you remember any salient details of the transformation.
To use an existing datum, click Select and select the datum in the list that displays.
Interpolation transformations require grid files for both the source and target datums.
Analytic formulas do not require grid files. If you select this method, indicate which conversion method to use. See the Concept tab for this topic for information on the methods available.
Null transformations transform data between two datums that have no significant differences.
Parameters can include any of the following:
Geocentric Translation
Axis Rotation of Arc
Axis Translation
Scale
The grid files that use this format appear in the left-hand list.
Click + to browse to grid files on your system. AutoCAD Map 3D toolset does not check whether your grid file is in the selected format. You must ensure that the format and the grid file match.
You can add one or more grid files. Grid files are added in their default order, but you can change their position with the Up and Down buttons. If the coverage of the files does not overlap, the order of the files does not matter. However, when converting a point in an overlapping area of grid files, the first grid file listed is used. To remove a grid file you added, select it and click -.
Values are expressed in degrees. Longitude parameters are relative to Greenwich.
To edit any displayed value, click Edit for that section. Make your changes and click Next to cycle through the remaining screens and return to the summary.
The conversion is performed using the new transformation parameters. AutoCAD Map 3D toolset displays and verifies the results.