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 657 NMEA output:
Latitude and longitude coordinates displayed on any NMEA repeater do not match the coordinates on the 657. 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 657. 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 657 chart window to where they should be.
The positions of the boat, waypoints, tracks, and lines of latitude and longitude on the 657 chart window remain unchanged.
Applying a map shift
1Move the boat to a known point on the chart, for example a marina berth.
2In the Chart setup menu, select
Map shift.
3Move the cursor to the position on the chart where the boat actually is.
4Press 
and select Set.
5Press 
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 657 chart window.
1In the Chart setup menu, select
Map shift.
2Press 
and select Clear.
3Press 
.
General submenu |
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Plotter mode | Normal: only scales available on the chart card can be displayed | ||
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| If you press | or | to select a chart scale which is not available, on the chart card, the |
| chart window will change to this scale but will only display the boat position and track (if enabled). | ||
| The rest of the display is white with black crosshatch lines and no chart information is displayed. This | ||
| is useful to zoom to a small scale to track small boat movements or if there is no detailed chart for | ||
| an area |
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Mixing levels | Mixes lower detail charts with higher detail charts on chart boundaries | ||
| Lower detail chart is not shown | ||
| Lower detail chart shown; this is slower to redraw | ||
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Anticlutter | Names and icons shown. Note: this is independent of the change in detail shown at different | ||
| zoom levels |
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| Hides some less important names and icons to make the chart clearer | ||
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Value added data | Non marine chart data shown | ||
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Northstar Explorer 657 Installation and Operation Manual | 63 |
