Glossary
Appendix B
GSR2600
105
RTCA -
Radio Technical Commission for Aeronautics, an
organization which developed and defined a message format for
differential positioning.
RTCM -
Radio Technical Commission for Maritime Services, an
organization which developed and defined the SC-104 message
format for differential positioning.
RTK -
Real-time kinematic, a type of differential positioning
based on observations of carrier phase.
Selective Availability (SA) -
The method used by the United
States Department of Defense to control access to the full
accuracy achievable by civilian GPS equipment (generally by
introducing timing and ephemeris errors).
A Department of Defense program controls the accuracy of
pseudorange measurements, whereby the user receives a false
pseudorange which is in error by a controlled amount.
Differential GPS techniques can reduce these effects for local
applications.
Site -
A location or survey point where GPS data is collected.
Slant height -
The distance from the survey marker to the edge
of the antenna ground plane. Using the slant height and radius
of the GPS antenna, the true vertical height or HI of the antenna
can be determined. The HI is used in the processing to determine
the location of the survey marker on the ground.
Spherical Error Probable (SEP) -
The radius of a sphere,
centered at the user’s true location, that contains 50 percent of
the individual three-dimensional position measurements made
using a particular navigation system.
Spheroid -
Sometimes known as ellipsoid; a perfect
mathematical figure which very closely approximates the geoid.
Used as a surface of reference for geodetic surveys. The geoid,
affected by local gravity disturbances, is irregular.
Standard Positioning Service (SPS) -
A positioning service
made available by the United States Department of Defense
which will be available to all GPS civilian users on a continuous,
worldwide basis (typically using C/A Code).
750-1-0093 Rev 1.book Page 105 Friday, June 28, 2002 4:02 PM
