RightWay GPS Navigator RW 430 Guia do Utilizador descarregar pdf (Página 87)

GPS RTK Base GPS Receiver User Guide 85

Glossary

differential

correction

Differential correction is the process of correcting GPS data collected on a

rover with data collected simultaneously at a base station. Because the base

station is on a known location, any errors in data collected at the base

station can be measured, and the necessary corrections applied to the rover

data.

Differential correction can be done in real-time, or after the data has been

collected by postprocessing.

differential GPS See real-time differential GPS.

DOP Dilution of Precision. A measure of the quality of GPS positions, based on the

geometry of the satellites used to compute the positions. When satellites are

widely spaced relative to each other, the DOP value is lower, and position

accuracy is greater. When satellites are close together in the sky, the DOP is

higher and GPS positions may contain a greater level of error.

PDOP (Position DOP) indicates the three-dimensional geometry of the

satellites. Other DOP values include HDOP (Horizontal DOP) and VDOP

(Vertical DOP), which indicate the accuracy of horizontal measurements

(latitude and longitude) and vertical measurements respectively. PDOP is

related to HDOP and VDOP as follows: PDOP = HDOP + VDOP

dual-frequency

GPS

A type of receiver that uses both L1 and L2 signals from GPS satellites. A

dual-frequency receiver can compute more precise position fixes over longer

distances and under more adverse conditions because it compensates for

ionospheric delays.

EGNOS European Geostationary Navigation Overlay Service. A satellite-based

augmentation system (SBAS) that provides a free-to-air differential

correction service for GPS. EGNOS is the European equivalent of WAAS,

which is available in the United States.

elevation mask The angle below which the receiver will not track satellites. Normally set to

10 degrees to avoid interference problems caused by buildings and trees,

atmospheric issues, and multipath errors.

ellipsoid An ellipsoid is the three-dimensional shape that is used as the basis for

mathematically modeling the earth’s surface. The ellipsoid is defined by the

lengths of the minor and major axes. The earth’s minor axis is the polar axis

and the major axis is the equatorial axis.

emphemeris /

ephemerides

A list of predicted (accurate) positions or locations of satellites as a function

of time. A set of numerical parameters that can be used to determine a

satellite’s position. Available as broadcast ephemeris or as postprocessed

precise ephemeris.

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