How To: Install a new NTv2 geographic transformation and grid file for use in ArcGIS Desktop
The instructions provided describe how to install a new NTv2 geographic transformation grid in ArcGIS Desktop.
Note: The NTv2 transformation grid file has a .gsb extension.
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 ArcGIS Desktop 10 C:\Program Files\ArcGIS\Desktop 10.0\pedata\ntv2
For ArcGIS 9.3.1 and previous versions C:\Program Files\ArcGIS\pedata\ntv2
Note: For 64-bit operating systems, ArcGIS Desktop is installed at C:\Program Files (x86).
Copy the NTv2 grid file into the new folder.
Open ArcToolbox > Data Management Tools > Projections and Transformations > Create Custom Geographic Transformation.
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'.
For the Input Geographic Coordinate System, click the Browse button > Select > Geographic Coordinate Systems folder, and select the NTv2 grid's existing Geographic Coordinate System.
For the Output Geographic Coordinate System, click the Browse button > Select > Geographic Coordinate Systems folder, and select the desired Geographic Coordinate System for the NTv2 grid.
From the Method drop-down menu, select NTv2.
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'.
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 will need to be shut down and restarted in order to use the new transformation in the map document.
Note: The NTv2 grid file and the new geographic transformation file are not removed when ArcGIS 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.
When the new Geographic Transformation has been created, the Projection Engine in ArcGIS Desktop will execute the transformation in either direction, as the software does with the transformations installed with the program. For more information refer to the link below to article "Select the correct geographic (datum) transformation when projecting between datums".