Navman Datahelm 8120 Installation And Operation Manual page 59

NMEA datum offset
If you select a map datum other than WGS
84, the map datum offset can be applied to
latitude and longitude coordinates sent on
the Instrument NMEA output:
Latitude and longitude coordinates
displayed on any NMEA repeater do not
match the coordinates on the Instrument.
Latitude and longitude coordinates
broadcast on any NMEA VHF transmitter
will be the same as the coordinates on a
WGS 84 chart.
Latitude and longitude coordinates
displayed on any NMEA repeaters match
the coordinates on the Instrument.
However, latitude and longitude
coordinates broadcast on any NMEA VHF
transmitter will be slightly offset from
coordinates on a WGS 84 chart.
Map shift
CAUTION
!
WARNING
!
Warning: Map shift is for eliminating
DANGER
minor offsets. It should not be used if the
correct datum is available. Use map shift
CAUTION
with caution: incorrect application will
cause incorrect boat positions.
Some charts have consistent position errors.
To correct this, apply a map shift. After a map
shift:
The positions of cartographic features
(such as land, rocks, buoys and depth
contours) move on the Instrument chart
window to where they should be.
The positions of the boat, waypoints,
tracks, and lines of latitude and longitude
on the Instrument chart window remain
unchanged.
Applying a map shift
1 Move the boat to a known point on the
chart, for example a marina berth.
2 In the Chart setup menu, select
Map shift.
3 Move the cursor to the position on the
chart where the boat actually is.
59
and select Set.
4 Press
MENU
5 Press to set the new map shift.
ESC
The boat will now be displayed at its
actual location.
Clearing the map shift
Clearing the map shift removes any map
shift from the cartographic features on the
Instrument chart window.
1 In the Chart setup menu, select
Map shift.
and select Clear.
2 Press
MENU
3 Press .
ESC
8120 Installation and Operation Manual