and cartographic features such
as land, rocks, buoys and depth
contours.
Use Map datum to select the unit
map datum to match the datum of
the paper chart. Then, the latitude
and longitude coordinates of objects
shown on the unit will change to
match the corresponding coordinates
on the paper chart.
Setting map datum
In the Chart setup menu >
Map datum > Select the map
datum for the paper chart you are using.
If you select a datum other than
WGS 84 the unit asks if you want to
apply the NMEA datum offset (see
below).
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
unit’s NMEA output:
Latitude and longitude coordinates
shown on any NMEA repeater do not
match the coordinates on the unit.
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
shown on any NMEA repeaters match
the coordinates on the unit. However,
latitude and longitude coordinates
broadcast on any NMEA VHF
transmitter will be slightly offset from
coordinates on a WGS 84 chart.
Map shift 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 chart window
to where they should be.
The positions of the boat, waypoints,
tracks, and lines of latitude and
longitude on the unit chart window
remain unchanged.
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