Specifications

difference between an AGD66 and a WGS 84 charted position can be up to 200 meter's (0.1 miles).
This could be the difference between one side of a reef and the other!
If you plot a GPS latitude and longitude on a chart which uses a different datum, you must apply
some corrections otherwise you will plot your position in the wrong place.
Mapping software such as
OziExplorer will usually do these corrections for you.
CHECK YOUR DATUMS CAREFULLY
all latitudes and longitudes which you use for navigation must
relate to the SAME datum.
How does OziExplorer Handle Datums?
OziExplorer can handle many different datums and knows how to translate positions from one datum
to another. Provided you have entered your datums correctly OziExplorer will ensure that all
positions are translated to the correct datum as required.
How to set Datums in OziExplorer
Setting Datums incorrectly will make the positions used in OziExplorer incorrect.
The Map Datum
- (set in the Map Calibration screen) must always be set to be the same as the
Datum the map was drawn in. (Actually to be more correct the Map Datum must be set to be the
same as the Datum used to obtain the positions used to calibrate the map). Changing the Map Datum
to anything else will definitely cause positions to be calculated and displayed on the map incorrectly.
The Data File Datum
can be set to any datum you like. It only affects the positions stored in the
file. It is only provided as a configurable option in case you want to work directly with the data file.
The GPS Upload/Download Datum
- must always be set to match the datum your GPS expects its
position data to be transmitted in.
For Garmins this Datum should always be set to
WGS 84.
For Magellans this Datum should always be set to
WGS 84.
For Lowrance/Eagle - Most should have this Datum set to WGS 84 but care should be taken if
using a GlobalNav 200 or Eagle Explorer as certainly some of these units require the
Upload/Download Datum to be set to the same datum as the GPS is set to.
The GPS NMEA Output Datum
- must always be set to the same datum that the GPS uses for the
positions it sends in the NMEA sentences.
For Garmins the Datum must be set to the same as the Datum setting in the GPS. If using
moving map mode and you change the GPS datum then you should always change this datum
also.
For Magellans you need to check this, some models output in WGS84 and others such as the
315/320 output in the Datum the GPS is set to.
For Lowrance/Eagle - Most should have this Datum set to WGS 84 but care should be taken if
using a GlobalNav 200 or Eagle Explorer as certainly some of these units require the NMEA
Output Datum to be set to the same datum as the GPS is set to.
Adding User Datums
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OziExplorer Help Contents