Geodetic Datum; Correcting Gps Position - Furuno GD-3300 Operator's Manual

10.6 Geodetic Datum

10.7 Correcting GPS Position

8. Press the [NAV DATA] key to display the navigation data dis-
play.
The indication "CST" appears at the top of the display. When cold
start is completed, "CST" is replaced by "2D" or "ACQ." Cold start
takes about two minutes to complete.
A nautical chart is usually made by either trigonometrical survey or
astronomical survey and according to the geodetic chart standards of
the country it is used in. For example, the USA uses the system called
Clarke; India, Everest, and Japan, Bessel. Accordingly when you are
getting position fixes by GPS in the USA, the system should be Clarke
so you don't get a position fix which shows you're somewhere off-
shore when you're actually moored to a dock.
While the use of one category of chart systems is fine if you don't do
transoceanic voyages, ocean-going vessels may require all catego-
ries to get reliable position information. To solve this inconvenience,
a standard chart system was adopted by GPS: the WGS-84.
Selecting chart system
Although the WGS-84 system is now widely used the other catego-
ries of charts still exist. Thus it is necessary to apply a correction
value to the WGS-84 to match it to local geodetic systems.
The GD/GP-3300 can perform this calculation automatically if you
tell it what type of chart you're using. For Clarke charts, for example,
select NAD (North America 1992). Select the chart system used, not
the area where the boat is sailing.
You may apply an offset to GPS position to further refine its accu-
racy.
1. Press [MENU] and [8], and then press [ ] to set the cursor on
PAGE CHANGE (TO GPS INITIAL SETTINGS).
2. Select DELTA LATITUDE and enter latitude offset.
3. Select DELTA LONGITUDE and enter longitude offset.
4. Press the [ENT] key.
5. Press the [MENU] key.
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