2011

Datum Shift Issues for North American Users
If the source and destination coordinate systems use different datums,
AutoCAD Map 3D automatically performs a datum (page 2059) shift. Within
North America, this is most often a shift between the NAD27 and NAD83
datums.
For United States users, AutoCAD Map 3D uses the freely distributable
NADCON grid data files (page 105) supplied by USGS.
Canadian users can use either version 1 or version 2 of the Canadian National
Transformation supplied by Geomatics Canada. If both versions of the
Canadian National Transformation are present, AutoCAD Map 3D uses version
2.
WARNING Geomatics Canada no longer supports version 1, and many Canadian
provinces do not consider it to produce valid results. If you are in Canada and
doing NAD Shifts, it is recommended that you use version 2.
See also:
■
Creating New Coordinate Systems (page 89)
■ Grid Data Files for Australia and New Zealand (page 109)
■ Grid Data Files for the United States (page 105)
■ Coordinate System Files (page 113)
■ Australian Datum Transformation and Coordinate System Changes (page
110)
To use version 2 of the Canadian National Transformation
1 Obtain a copy of the data file.
Contact Information Services, Geodetic Survey Division, Geomatics
Canada
615 Booth Street
Ottawa, Ontario, K1A 0E9
[phone]
http://www.geod.nrcan.gc.ca
2 Once you have the file, copy it into the Autodesk shared coordinate
system folder, by default C:\Documents and Settings\All Users\Application
112 | Chapter 2 Setting Up