Leica GPS900 Series, Technical Reference Manual

Page: 185 / 287

Working with Determine Coord System GPS900 185
28 Working with Determine Coord System
28.1 An Overview of the Program
Description • GPS measured points are always stored based on the global geocentric datum known as
WGS 1984. Most surveys require coordinates in a local grid system, for example, based
on a country’s official mapping datum or an arbitrary grid system used in a particular area
such as a construction site. To convert the WGS 1984 coordinates into local coordinates
a coordinate system needs to be created. Part of the coordinate system is the transfor-
mation used to convert coordinates from the WGS 1984 datum to the local datum.
• The Determine Coordinate System application program allows:
• the parameters of a new transformation to be determined.
• the parameters of an existing transformation to be recomputed.
Transformations A transformation is the process of converting coords from one geodetic datum to another.
Transformation requirements
• Transformation parameters.
• In some cases a local ellipsoid.
• In some cases a map projection.
• In some cases a geoid model.
Transformation parameters
A transformation consists of a number of shifts, rotations and scale factors, depending on
the type of transformation used. Not all of these parameters are always required. These
parameters may already be known, or may need to be computed.
Description of transformations
A Onestep transformation is provided on RX900.