ashtech DG14, Reference Manual

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Coordinate Transformation 79
This chapter discusses the coordinate transformation features of your receiver.
GPS determines the three-dimensional positions of surveyed points based on the
WGS-84 datum. These coordinates are either presented as geocentric Cartesian
coordinates (X,Y,Z) values or geodetic coordinates (latitude, longitude, ellipsoidal
height).
There are circumstances where it would be desirable to have positions represented
in a different reference frame or format, i.e. based on a different datum or projected
onto a plane (grid coordinates).
The DG16 provides the following on-board tools to transform WGS-84 coordinates
into various formats and reference frames:
1. Datum-to-Datum transformation
Using this feature, WGS-84 coordinates can be transformed into coordinates
based on another datum.
2. Datum-to-Grid conversion
With this tool, a grid system can be defined to convert geodetic coordinates
into grid coordinates.
3. Elevation Modeling
Using an on-board geoid model, ellipsoidal heights can be transformed into
orthometric heights using this capability.