NorthStar MX500 Operator's & Installation Manual page 260

Operator's Manual
DEAD RECKONING
DECCA LINES OF POSITION (LOPs)
DEFAULT
DEVIATION (COMPASS)
DGPS
DIFFERENTIAL GPS (DGPS)
DILUTION OF PRECISION (DOP)
246
The process of determining changes of position based on mea-
sured speed and course over measured time periods.
The phantom Decca Lines of Position used in the navigator are
based on mathematical models. Local deviations in propagation
speed are not included. The calculated positions may therefore
differ from positions obtained from dedicated Decca receivers by
several hundred meters.
A condition that the navigator assumes automatically if no other
condition is initiated by the operator.
Magnetic compass reading error due to local magnetic field influ-
ences.
See DIFFERENTIAL GPS.
A method of refining GPS position solution accuracy by modifying
the locally computed position solution with correction signals from
an external reference GPS CDU (monitor).
A figure of merit for the quality of GPS-derived position and clock
bias estimates, based on the geometry of the selected satellite con-
stellation. The smaller the DOP, the less the magnification of the
range measurement error into position and clock bias errors. Gen-
erally, the more spread out the satellites, the lower the DOP. The
most common DOPs are as follows:
HDOP - Horizontal dilution of precision.
GDOP - Geometric dilution of precision.
PDOP - Position dilution of precision.
VDOP - Vertical dilution of precision.
Glossary
Version 3.0