2011

■ Overview of Grid Data Files and Datum Shift Issues (page 103)
■ Grid Data Files for the United States (page 105)
■ 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
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.
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 the United States
AutoCAD Map 3D uses North American Datum Conversion (NADCON) grid
data files from the National Geodetic Survey to obtain latitude and longitude
shift information for converting between coordinate systems within the United
States. A pair of grid data files is required for each area or state covered: a .las
file is required for latitude shift values (latitude seconds) and a .los file for
longitude shift values (longitude seconds).
The NADCON files include grid data files for transformations between NAD83
and state readjustments to HARN (High Accuracy Resolution Network) projects.
The .las and .los files are in the public domain and are distributed with
AutoCAD Map 3D. The files are stored in the Autodesk shared coordinate
system folder, by default C:\Documents and Settings\All Users\Application
Data\Autodesk\Geospatial Coordinate Systems\Usa\Nadcon.
Creating New Coordinate Systems | 105