6.6 Coordinate systems and transformations
GNSS systems use a WGS84 coordinate system for
positioning. WGS84 is a geodetic coordinate system
where a position is specified as latitude, longitude,
and altitude. Latitude is expressed as an angle from
the equator (Fig. 76). Longitude is expressed as an
angle from the prime meridian (Greenwich meridian).
Altitude is height compared to the WGS84 reference
ellipsoid (Fig. 77). An ellipsoid can be seen as a
simplified presentation of the surface of the Earth.
Project files, for example Digital Terrain Models
(DTM), use Cartesian coordinate systems. This
means that a transformation from a geodetic system
to a Cartesian system has to be carried out. When
transforming geodetic coordinates to Cartesian
coordinates, geodetic coordinates are projected from
an ellipsoid onto a plane.
A Cartesian coordinate system specifies a position by
using metric units instead of angles. The coordinates that specify a point on a plane are typically
called northing and easting (Fig. 76), or X and Y. The Cartesian X, Y, and Z coordinates in the
system are the result of coordinate transformation, offset parameters, and the Geoid Model that
has been selected.
Note!
Using the correct coordinate system is very important when working with tasks
(project files) that have absolute coordinates. When working with tasks without
absolute coordinates (for example if only the height offset to a stake has been
defined), any coordinate system that is suitable for the working area can be used.
There are two ways to carry out coordinate transformations.
1. Use national or regional coordinate systems.
2. Create a local coordinate system for each jobsite
Fig.
77. Geoid Model
User Manual. Xsite PRO SPI 14.2 Page 68 / 77
Fig.
76. Geodetic coordinates
Summary of Contents for XSITE PRO SPI 14.2
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