Map Datums - Garmin eTrex Summit - Hiking GPS Receiver Owner's Manual

Setup Page
Units Page
Eighteen position formats are available in the eTrex Summit.
Data entry pages for the User
Grid Format and the User
Datum Setup allow you to
configure the eTrex Summit
for compatibility with custom
designed grids. We recom-
mend surfing the net for links
to Garmin user-grid and user
User
datum information. There are
Datum
also excellent navigation and
User Grid
GPS articles available on-line
which will enhance your
overall knowledge of GPS.
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Position Format
The default position format (and the one most commonly used) for the eTrex Summit is
latitude and longitude in degrees and minutes (hdddº mm.mmm). You may also choose from
17 other position formats. There is also a "User" position format which allows you to approxi-
mate custom-designed grids. For more information on grids and datums we recommend you
visit the National Imagery and Mapping Agency at http://www.nima.mil .
To change the Position Format:
1. Press the PAGE button and switch to the MENU Page. Press the UP or DOWN button and
highlight 'SETUP'. Press ENTER. Press the UP/DOWN buttons to select 'UNITS'. Press
ENTER. The UNITS Page appears.
2. Press the UP or DOWN button to select the 'POSITION FRMT' field. Press ENTER.
3. Press the UP or DOWN button to select the desired format. Press ENTER. Press PAGE to
get back to the page of your choice.

Map Datums

A map datum is a reference model of the earth' s shape. Every map uses a map datum. The
map datum is usually listed in the title block of the map. If you are comparing GPS coordi-
nates to a paper map or other reference, the map datum in the eTrex Summit should match
the horizontal map datum used to generate the chart or other reference.
The default datum in the eTrex Summit is WGS 84 (World Geodetic Survey, 1984). You
should only change the datum if you are using maps or charts that specify a different datum
than WGS 84. If no datum is specified, you can select each datum applicable to your region
until you find the datum that provides the best positioning at a known point. You may also
choose the "User" datum for use with custom-designed grids.