Navigation General · Electronic Nav — Chart Datum (WGS-84)
A GPS receiver outputs positions referenced to WGS-84; if the chart in use is on a different datum, the navigator must:
- AIgnore the difference
- BReverse latitude and longitude
- CApply the datum shift noted on the chart before plotting the GPS position✓ Correct
- DSwitch off the GPS
Explanation
Older charts may be on a local datum differing from WGS-84 by hundreds of meters. Plotting a raw GPS position on such a chart without applying the stated datum correction can place the vessel dangerously off its true charted position.
Authority: Bowditch; chart datum notes
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