Northstar
Explorer 557/567
Installation and Operation Manual
51
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 557/567
NMEA output:
Latitude and longitude coordinates
displayed on any NMEA repeater do not
match the coordinates on the 557/567.
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 557/567. However, latitude
and longitude coordinates broadcast on any
NMEA VHF transmitter will be slightly offset
from coordinates on a WGS 84 chart.
Map shift
!
WARNING
Map shift is for eliminating minor offsets.
It should not be used if the correct datum
is available. Use map shift 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 557/567 chart window to where
they should be.
The positions of the boat, waypoints, tracks,
and lines of latitude and longitude on the
557/567 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.
4 Press
and select
Set.
5 Press
to set the new map shift. 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 557/567
chart window.
1
In the Chart setup menu, select
Map
shift.
2 Press
and select Clear.
3 Press
.
