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Reference
Map Datums
Eighteen position formats are
available in the eTrex Summit.
Data Entry Pages exist
for the User Grid Format
and the User Datum
Setup. These pages allow
you to configure the eTrex
Summit for compatibility
with custom designed
grids. We recommend
surfing the net for links to
Garmin user-grid and
user datum information.
There are also excellent
navigation and GPS
articles available on-line
which will enhance your
overall knowledge of GPS.
44
Position Format
The default position format (and the one most commonly
used) for the eTrex Summit is latitude and longitude in de-
grees and minutes (hdddº mm.mmm'). You may also choose
from 17 other position formats. There is also a "User" posi-
tion format which allows you to approximate custom-de-
signed grids. For more information on grids and datum we
recommend you visit the National Imagery and Mapping
Agency at http://www.nima.mil.
To change the Position Format (grid):
1. Press the PAGE Button and switch to the 'MENU'
Page. Press the UP or DOWN Button and highlight
'SETUP'. Press ENTER. Use the UP/DOWN buttons
to select 'UNITS'. Press ENTER. The 'UNITS' Page
appears.
2. Press the UP or DOWN Button and select the
'POSITION FRMT' field. Press ENTER.
3. Press the UP or DOWN Button and 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 coordinates 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.
UA-1005.046
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