Install a new NTv2 geographic transformation and grid file for use in ArcMap

Summary

The instructions provided describe how to install a new NTv2 geographic transformation grid in ArcMap.

Note:
The NTv2 transformation grid file has a .gsb extension.

Procedure

1. Using Windows Explorer, create a new folder at the appropriate path below, and name the folder with the name of the country or area to which the transformation will be applied.

Warning:
The new folder name must be a single word and in lower case letters. No spaces are permitted in the folder name.

For ArcMap 10
C:\Program Files\ArcGIS\Desktop 10.0\pedata\ntv2

For ArcMap 9.3.1 and previous versions
C:\Program Files\ArcGIS\pedata\ntv2

Note:
For 64-bit operating systems, ArcMap is installed at C:\Program Files (x86).

2. Copy the NTv2 grid file into the new folder.
3. Open ArcToolbox > Data Management Tools > Projections and Transformations > Create Custom Geographic Transformation.
4. In the Geographic Transformation Name box, type in a name for the transformation.

Warning:
The transformation name cannot contain spaces, but underscores can be used. The transformation name is in the format 'Input_GCS_To_Output_GCS'.

5. For the Input Geographic Coordinate System, click the Browse button, select the Geographic Coordinate Systems folder, and select the NTv2 grid's existing Geographic Coordinate System.
6. For the Output Geographic Coordinate System, click the Browse button, select the Geographic Coordinate Systems folder, and select the desired Geographic Coordinate System for the NTv2 grid.
7. To determine which Geographic Transformation is best to use for your data, refer to How To: Select the correct geographic (datum) transformation when projecting between datums.
8. Download and save the list of supported Geographic transformations that pertains to your version of the software.

Note:
This list includes an alphabetical list of all transformations that are available for your version of the software, the published accuracy of the transformation (in meters), and both a text description, and coordinates, describing the extent for which that transformation can be used. If the data falls outside the area the transformation is defined for, the data will NOT be transformed.

9. From the Method drop-down menu, select NTv2.
10. In the Parameters section, under Value, populate the field with the new folder name, followed by a forward slash (/) and the GSB file name.

Note:
For example, the Value field for a new transformation for Scotland with the name scotland1.gsb would be populated with 'scotland/scotland1.gsb'.

11. In the Create Custom Geographic Transformation dialog box, click OK.
    Version 10.0:
    The custom transformation file is created in '%User_Profile%\Application Data\ESRI\Desktop10.0\ArcToolbox\Custom Transformations'.
    
    Version 9.3.1 and prior versions:
    The custom transformation file is created in '%User_Profile%\Application Data\ESRI\ArcToolbox\Custom Transformations'.
    The file has the name assigned in Step 3 above with a .gtf extension. The new transformation will be available for use in the Project Tool in ArcToolbox, as well as in the Geographic Coordinate System Transformations dialog box in ArcMap.

Warning:
If ArcMap is open when the new transformation is created, ArcMap must be shut down and restarted to use the new transformation in the map document.

Note:
The NTv2 grid file and the new geographic transformation file are not removed when ArcMap is uninstalled.

Note:
To install the custom geographic transformation on another computer, copy the .GTF file to the other computer at the same path in the User Profile directory, and install the transformation grid .GSB file on that computer as described in Steps 1 and 2.

10. When the new Geographic Transformation has been created, the Projection Engine in ArcMap executes the transformation in either direction, as the software does with the transformations installed with the program. For more information refer to the article How To: Select the correct geographic (datum) transformation when projecting between datums.