Northstar
Explorer 660
Installation and Operation Manual
50
Map datum
Explorer 660 GPS positions are based on a
worldwide reference (datum) known as WGS
84. Most paper charts are based on WGS 84.
However, some paper charts are based on other
datums In these cases, the latitude and longitude
coordinates of objects on the Explorer 660 chart
display are different to the latitude and longitude
coordinates of these objects on the paper chart.
This applies to all objects, such as the boat,
waypoints, tracks, lines of latitude and longitude
and cartographic features such as land, rocks,
buoys and depth contours.
Use
Map datum
to select the Explorer 660 map
datum to match the datum of the paper chart.
Then, the latitude and longitude coordinates of
objects displayed on the Explorer 660 will change
to match the corresponding coordinates on the
paper chart.
Setting map datum
1
In the Chart setup menu, select
Map
datum
.
2
Select the map datum for the paper chart you
are using.
3
The Explorer 660 asks if you want to apply
the datum offset to latitude and longitude
coordinates sent on the NMEA output. The
options are:
Yes
: Latitude and longitude coordinates
displayed on any NMEA repeaters match the
coordinates on the Explorer 660. However,
latitude and longitude coordinates broadcast
on any NMEA VHF transmitter will be slightly
offset from coordinates on a WGS 84 chart.
No
: Latitude and longitude coordinates
displayed on any NMEA repeater do not
match the coordinates on the Explorer
660. Latitude and longitude coordinates
broadcast on any NMEA VHF transmitter will
be the same as the coordinates on a WGS 84
chart.
!
WARNING
When you change to a chart with a different
datum, change the Explorer map datum
again.
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 Explorer 660 chart display to
where they should be.
The positions of the boat, waypoints, tracks,
and lines of latitude and longitude on the
Explorer 660 chart display remain unchanged.
!
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.
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
ENTER
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 Explorer
660 chart display.
1
In the Chart setup menu, select
Map shift
.
2 Press
MENU
and select
Clear
.
Waypoints
Controls how waypoints are displayed on the
chart. The options are:
Hide all
: No waypoints are displayed
(except for waypoints on any selected route).
Show all
: All waypoints are displayed.
Selected
: Waypoints with their display
option set to Icon or I+N (Icon and Name) are
displayed (see section 5).
Chart display options
The other chart setup options allow an extensive
range of chart card features to be shown.
Configure the most useful display format.
