2011

For more information about NADCON grid data files, refer to the National
Geodetic Survey web site.
See also:
■ Datum Shift Issues for North American Users (page 112)
■ Coordinate System Files (page 113)
■ Overview of Grid Data Files and Datum Shift Issues (page 103)
■ Grid Data Files for Australia and New Zealand (page 109)
■ Australian Datum Transformation and Coordinate System Changes (page
110)
To set up a new grid data file for the United States
1 When you obtain a new grid data file, copy it into the appropriate folder
under the Autodesk shared coordinate system folder, by default
C:\Documents and Settings\All Users\Application Data\Autodesk\Geospatial
Coordinate Systems\Usa\Nadcon.
2 Open the appropriate GDC file in any text editor or word processor that
can produce an ASCII file, such as Notepad or Wordpad.
NOTE Back up GDC files before you edit them, so you can restore them to
their previous state, if necessary.
3 Edit the file to point to the name and location of your new grid data file.
4 Make other changes needed, such as rearranging or replacing grid data
files, changing the fallback
datum (page 2059) definition, or adding
comments.
Grid Data Files for France
AutoCAD Map 3D comes with a grid data catalog file (RgfToNtf.gdc) and a
national grid data file (gr3df97a.txt )for France. This file is installed in a folder
under the Autodesk shared coordinate system folder, by default C:\Documents
and Settings\All Users\Application Data\Autodesk\Geospatial Coordinate Systems.
Several French municipalities have developed local grid data files that allow
for more precise transformations within their respective regions. You can
obtain municipal grid data files from the local GIS or Survey department. If
108 | Chapter 2 Setting Up