9.14 Configuring the Datum
The Datum is a reference surface that has 5 parameters :
•
Point of the ground;
•
geoidal height;
•
reference ellipsoid;
•
geodesic coordinates of each starting point ;
•
azimuth from this point.
The GPS TrackMaker® program makes the conversion of more than 280 different parameters of datum, as shown
in
Datum Table
.
Choosing
List of datum supported by GPS option, the list of datum supported by most of Garmin® and Magellan®
GPS will be shown.
Keep in mind that each map may have been built using a specific datum. Then, in order to keep compatibility
among the different maps, it is necessary to change the datum used by the GPS TrackMaker®. In
Tools > Options
> Datum, choose the datum option that corresponds to the map used.
In GTM PRO® it is possible to create a
User Datum. For further information, see
Datum Defined by User
.
Example:
Data are collected with the GPS then transfers them to GPS TrackMaker®, which is configured for the WGS 84
Datum.
Then, a topographic chart created in the
Corrego Alegre datum is inserted in
GPS TrackMaker®
. Usually, the
datum is indicated in the bottom of the map charts.
When transferring to the map the data obtained with the GPS, probably the points will be located up to a few
hundreds of meters away from the real position.
In order to prevent this error, change the datum in the GPS TrackMaker® to
Corrego Alegre All coordinates
coming from the GPS will be converted to the map datum (
Corrego Alegre).
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Summary of Contents for TrackMaker
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