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Chapter 4: Setting Up the GPS Plotter 4-11
Datum Selection
You can select either WGS 84 or LOCAL datum. In LOCAL mode, you are
presented with a Datum Names list. Use the trackpad up/down to scroll
through the list; press ENTER to select the option and close the menu.
Note: When the datum (reference grid) is changed, the geographical
position of waypoints remains constant. However, the latitude/longitude
values change as a result of their having been calculated from a different
datum. When adding waypoints numerically to the waypoint list, or via
SeaTalk, NMEA, it is important that they are referenced to the same da-
tum in which the display is to be operated.
Position Offset
You can offset the vessel position to allow for differences between the
GPS and paper chart data. This may be useful if you are using a datum
that is not available on the Chartplotter, or if you are referring to a paper
chart drawn to unknown datum.
You can change the offset by moving the cursor to the known vessel
position. This offset is applied to all incoming position data. The default
offset value is zero.
When position offset is switched on, all displayed vessel position data is
annotated (C) to indicate it has been corrected.
To switch the position offset on/off:
Select the POSITION OFFSET option, then press the OFFSET OFF ON soft
key to toggle the option on/off. The last selected offset value is added to
position data and the vessel is displayed at the corrected position.
To set a new offset value:
Select the POSITION OFFSET option, then press the SET UP OFFSET soft key.
If necessary, position offset is automatically toggled on.
Use the trackpad to move the cursor to the required vessel position; the
cursor position is displayed in a position offset data box.
Press the ACCEPT OFFSET soft key, the vessel is displayed at the new
position. Press ENTER to return to the default display.
To set the offset value to zero:
Select the POSITION OFFSET option, then press the SET UP OFFSET soft key
Press the CANCEL OFFSET soft key. The position offset value is set to zero