User's Manual

SPSx50 Modular GPS Receiver User Guide 165
Glossary
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.
epoch The measurement interval of a GPS receiver. The epoch varies according to the survey
type: for real-time survey measurement it is set at one second; for postprocessed
survey measurement it can be set to a rate of between one second and one minute. For
example, if data measurement is measured every 15 seconds, loading data using
30-second epochs means loading every other measurement.
feature A feature is a physical object or event that has a location in the real world, which you
want to collect position and/or descriptive information (attributes) about. Features
can be classified as surface or non-surface features, and again as points,
lines/breaklines, boundaries/areas.
firmware The program inside the receiver that controls receiver operations and hardware.
GLONASS (Global Orbiting Navigation Satellite System)
GLONASS is a Soviet space-based navigation system comparable to the American GPS
system. The operational system contains 21 satellites in 3 orbital planes, with 3
on-orbit spares.
GNNS Global Navigation Satellite System
GSOF General Serial Output Format
HDOP (Horizontal Dilution of Precision)
Dilution of Precision (DOP) is 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.
HDOP is a DOP value that indicates the accuracy of horizontal measurements. Other
DOP values include VDOP (vertical DOP) and PDOP (Position DOP).
Using a maximum HDOP is ideal for situations where vertical precision is not
particularly important, and your position yield would be decreased by the vertical
component of the PDOP ( for example, if you are collecting data under canopy).
Horizontal Dilution
of Precision
See HDOP.
L1 The primary L-band carrier used by GPS satellites to transmit satellite data.
L2 The secondary L-band carrier used by GPS satellites to transmit satellite data.
L5 The third L-band carrier used by GPS satellites to transmit satellite data. L5 will
provide a higher power level than the other carriers. As a result, acquiring and tracking
weak signals will be easier.
Moving Base Moving Base is an RTK positioning technique in which both reference and rover
receivers are mobile. Corrections are sent from a ‘base’ receiver to a ‘rover’ receiver and
the resultant baseline (vector) has centimeter-level accuracy