NTv2
The Geographic Calculator supports the definition of a datum transformation based on the Canadian National Transformation Version 2.0 (Canadian NTV2) directly. The Canadian National Transformation originally defined an accurate transformation from NAD27 to NAD83 for Canada, but the method has been adopted by Australia, New Zealand, Spain, and several other locations around the world. The shift values for a geographic area are stored in a single grid file, representing latitude and longitude shifts (named with the extension .gsb). This transformation uses bilinear interpolation.
The Geographic Calculator uses grid files in a format published and provided by the Canadian Government. While the definition of this method is supported, it does require additional files to implement new datum transformations using this method.
Contact information is as follows:
Address: Natural Resources
Canada
Geodetic Survey Division
Room 440
615 Booth Street
Ottawa, Ontario
K1A 0E9
Phone: (613) 995-4410
Email: information@geod.NRCan.gc.ca
Web: https://www.geod.NRCan.gc.ca
Note: When browsing through the datasource some objects may be flagged with
a red exclamation point 
symbol.
These objects are incomplete definitions. The Geographic Calculator
includes a number of datum transformation definitions that require supplementary
data files to function properly. These objects are not able to be
used until the supplementary files are added. Some of these are
available at our website (https://www.bluemarblegeo.com), while others
are proprietary and must be purchased from a specific government agency.
NTv1
The NTv1 method is the earlier implementation of the Canadian National Transformation. This method is supported for legacy reference. The shift values for a geographic area are stored in a single grid file, representing latitude and longitude shifts (named with the extension .gsb). This transformation uses bilinear interpolation.