http://www.ocol.net/users/donegal/NAVSTAR.htm
CONTENTS
1) What is GPS
2) WAAS
3) eTrex Products
4) eTrex User Manuals
5) Glossary
6) Links
7) Dealers
8) $267 eTrex Summit model
9) $145 basic eTrex model
The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
HOW IT WORKS
GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.
A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.
HOW ACCURATE IS GPS?
Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. GARMIN's 12 parallel channel receivers are quick to lock onto satellites when first turned on and they maintain strong locks, even in dense foliage or urban settings with tall buildings. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. GARMIN GPS receivers are accurate to within 15 meters on average.
Newer GARMIN GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than three meters on average. No additional equipment or fees are required to take advantage of WAAS. Users can also get better accuracy with Differential GPS (DGPS), which corrects GPS signals to within an average of three to five meters. The U.S. Coast Guard operates the most common DGPS correction service. This system consists of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters. In order to get the corrected signal, users must have a differential beacon receiver and beacon antenna in addition to their GPS.
THE GPS SATELLITE SYSTEM
The 24 satellites that make up the GPS space segment are
orbiting the earth about 12,000 miles above us. They are
constantly moving, making two complete orbits in less than 24
hours. These satellites are travelling at speeds of roughly 7,000
miles an hour.
GPS satellites are powered by solar energy. They have backup
batteries onboard to keep them running in the event of a solar
eclipse, when there's no solar power. Small rocket boosters on
each satellite keep them flying in the correct path.
Here are some other interesting facts about the GPS satellites (also
called NAVSTAR, the official U.S. Department of Defense name for
GPS):
The first GPS satellite was launched in 1978.
A full constellation of 24 satellites was achieved in 1994.
Each satellite is built to last about 10 years. Replacements are
constantly being built and launched into orbit.
A GPS satellite weighs approximately 2,000 pounds and is about 17
feet across with the solar panels extended.
Transmitter power is only 50 watts or less.
What's the signal?
GPS satellites transmit two low power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.
A GPS signal contains three different bits of information: a
pseudorandom code, ephemeris data and almanac data.
1) The pseudorandom code is simply an I.D. code that identifies
which satellite is transmitting information. You can view this
number on your GARMIN GPS unit's satellite page, as it identifies
which satellites it's receiving.
2) Ephemeris data, which is constantly transmitted by each
satellite, contains important information about the status of the
satellite (healthy or unhealthy), current date and time. This
part of the signal is essential for determining a position.
3) The almanac data tells the GPS receiver where each GPS
satellite should be at any time throughout the day. Each
satellite transmits almanac data showing the orbital information
for that satellite and for every other satellite in the system.
SOURCES OF GPS SIGNAL ERRORS
Factors that can degrade the GPS signal and thus affect accuracy include the following:
Ionosphere and troposphere delays
The satellite signal slows as it passes through the atmosphere.
The GPS system uses a built-in model that calculates an average
amount of delay to partially correct for this type of error.
Signal multipath
This occurs when the GPS signal is reflected off objects such as
tall buildings or large rock surfaces before it reaches the
receiver. This increases the travel time of the signal, thereby
causing errors.
Receiver clock errors
A receiver's built-in clock is not as accurate as the atomic
clocks onboard the GPS satellites. Therefore, it may have very
slight timing errors.
Orbital errors
Also known as ephemeris errors, these are inaccuracies of the
satellite's reported location.
Number of satellites visible
The more satellites a GPS receiver can "see," the
better the accuracy. Buildings, terrain, electronic interference,
or sometimes even dense foliage can block signal reception,
causing position errors or possibly no position reading at all.
GPS units typically will not work indoors, underwater or
underground.
Satellite geometry/shading
This refers to the relative position of the satellites at any
given time. Ideal satellite geometry exits when the satellites
are located at wide angles relative to each other. Poor geometry
results when the satellites are located in a line or in a tight
grouping.
Intentional degradation of the satellite signal
Selective Availability (SA) is an intentional degradation of the
signal once imposed by the U.S. Department of Defense. SA was
intended to prevent military adversaries from using the highly
accurate GPS signals. The government turned off SA in May 2000,
which significantly improved the accuracy of civilian GPS
receivers.
LEARN MORE ABOUT GPS
For more detailed information about GPS and how it works,
download the GPS Guide for beginners from http://www.garmin.com/support/userManual.html
gps4beg.pdf is a 524K GPS Guide for Beginners.
Who uses GPS? GPS has a variety of applications on land, at sea and in the air. Basically, GPS is usable everywhere except where it's impossible to receive the signal such as inside most buildings, in caves and other subterranean locations, and underwater. The most common airborne applications are for navigation by general aviation and commercial aircraft. At sea, GPS is also typically used for navigation by recreational boaters, commercial fishermen, and professional mariners. Land-based applications are more diverse. The scientific community uses GPS for its precision timing capability and position information.
Surveyors use GPS for an increasing portion of their work. GPS offers cost savings by drastically reducing setup time at the survey site and providing incredible accuracy. Basic survey units, costing thousands of dollars, can offer accuracies down to one meter. More expensive systems are available that can provide accuracies to within a centimeter.
Recreational uses of GPS are almost as varied as the number of recreational sports available. GPS is popular among hikers, hunters, snowmobilers, mountain bikers, and cross-country skiers, just to name a few. Anyone who needs to keep track of where he or she is, to find his or her way to a specified location, or know what direction and how fast he or she is going can utilize the benefits of the global positioning system.
GPS is now commonplace in automobiles as well. Some basic systems are in place and provide emergency roadside assistance at the push of a button (by transmitting your current position to a dispatch center). More sophisticated systems that show your position on a street map are also available. Currently these systems allow a driver to keep track of where he or she is and suggest the best route to follow to reach a designated location.
You've heard the term WAAS, seen it on packaging and ads for GARMIN products, maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters, 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.
The origins of WAAS
The Federal Aviation Administration (FAA) and the Department of Transportation are developing the WAAS program for use in precision flight approaches. Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity and availability. WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing and satellite orbit errors and provides vital integrity information regarding the health of each GPS satellite. Although WAAS has not yet been approved for aviation, the system is available for civilian use, such as for boaters and recreational GPS users.
How it Works
WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.
Who benefits from WAAS?
Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of WAAS is that it does not require additional receiving equipment while DGPS does.
Other governments are developing similar satellite-based differential systems. In Asia, it's the Japanese Multi-Functional Satellite Augmentation System (MSAS), while Europe has the Euro Geostationary Navigation Overlay Service (EGNOS). Eventually, GPS users around the world will have access to precise position data using these and other compatible systems.
It just keeps getting better 100 meters: Accuracy of the original GPS system, which was subject to accuracy degradation under the government-imposed Selective Availability (SA) program.
Telephone Garmen Customer Service Department at 1-800-800-1020 M-F 8-5 CST
Products and specification links are listed at http://www.garmin.com/outdoor/products.html
A PRODUCT COMPARISON form is at http://www.garmin.com/outdoor/compare.jsp
WAAS-enabled products:
GPS 76
GPSMAP 76
GPSMAP 176/176C
GPS 152
GPSMAP 182
GPSMAP 188 Sounder
GPSMAP 232
GPSMAP 238 Sounder
GPSMAP 295
eTrex Venture
eTrex Legend
eTrex Vista
GPSMAP 2006
GPSMAP 2010
GPS 17N
GPS V
GPSMAP 162
GPSMAP 168 Sounder
The eTrex Venture ($194 without Built-In Electronic Compass or Built-In Barometric Altimeter) is the cheapest eTrex unit that is designed to provide precise GPS positioning using correction data obtained from the Wide Area Augmentation System (WAAS). This product will provide position accuracy to less than three meters when receiving WAAS corrections. The memory capacity of one megabyte allows the eTrex Venture to accept downloaded information from GARMIN's new MapSource® Points of Interests CD-ROM. The CD enables users to download locations such as restaurants, hotels, shopping, and entertainment. Once the information is loaded into the unit, you can make a selection, and telephone and address information for a particular point of interest will appear on the screen. The CD also includes marine data such as lights, buoys, wrecks and obstructions. The eTrex Venture comes housed in a stylish, translucent green case.
Some more expensive WAAS models have rebates if bought with another product:: the eTrex Legend ($218 with rebate) has an 8MB memory but otherwise is about the same as the eTrex Venture.
2D OPERATING MODE
A two-dimensional GPS position fix that includes only horizontal
coordinates (no GPS elevation). It requires a minimum of three
visible satellites.
3D OPERATING MODE
A three-dimensional GPS position fix that includes horizontal
coordinates plus elevation. It requires a minimum of four visible
satellites.
ACCURACY
A measure of how close an estimate of a GPS position is to the
true location.
ACQUISITION TIME
The time it takes a GPS receiver to acquire satellite signals and
determine the initial position.
ACTIVE ANTENNA
An antenna that amplifies the GPS signal before it sends it to
the receiver.
ACTIVE LEG
The segment of a route currently being traveled. A segment is
that portion of a route between any two waypoints in the route.
ALMANAC DATA
Information transmitted by each satellite on the orbits and state
(health) of every satellite in the GPS constellation. Almanac
data allows the GPS receiver to rapidly acquire satellites
shortly after it is turned on.
ALTIMETER
An instrument for determining elevation, especially an aneroid
barometer used in aircraft that senses pressure changes
accompanying changes in altitude. The GARMIN eTrex Vista and
Summit models contain a basic GPS with a built-in barometric
altimeter.
ANALOG SIGNAL
The principal feature of analog signals is that they are
continuous. In contrast, digital signals consist of values
measured at discrete intervals.
ANTI-SPOOFING
Encryption of the P-code to protect the P-signals from being
"spoofed" through the transmission of false GPS signals
by an adversary.
ATOMIC CLOCK
A very precise clock that operates using the elements cesium or
rubidium. A cesium clock has an error of one second per million
years. GPS satellites contain multiple cesium and rubidium clocks.
AZIMUTH
The horizontal direction from one point on the earth to another
measured clockwise in degrees (0-360) from a north or south
reference line. An azimuth is also called a bearing.
BEACON
Stationary transmitter that emits signals in all directions; also
called a non-directional beacon. In DGPS, the beacon transmitter
also broadcasts pseudorange correction data to nearby GPS
receivers for greater accuracy.
BEARING
The compass direction from a position to a destination measured
to the nearest degree; also call an azimuth. In a GPS receiver,
bearing usually refers to the direction to a waypoint.
CARRIER FREQUENCY
The frequency of an unmodulated output of a radio transmitter.
The GPS L1 carrier frequency is 1575.42 MHz.
CARTOGRAPHY
The art or technique of making maps or charts. Many GPS receivers
have detailed mapping, or cartography, capabilities.
CODE DIVISION MULTIPLE ACCESS (CDMA)
A method whereby many radios use the same frequency but each one
has a unique code. GPS uses CDMA techniques with codes for their
unique cross-correlation properties.
CLOCK BIAS
The difference between the indicated clock time in the GPS
receiver and true universal time (or GPS satellite time).
CLOCK OFFSET
A constant difference in the time reading between two clocks,
normally used to indicate a difference between two time zones.
COARSE ACQUISITION CODE (C/A CODE)
The standard positioning signal the GPS satellite transmits to
the civilian user. It contains the information the GPS receiver
uses to fix its position and time. Accurate to 100 meters or
better.
COLD START
The power-on sequence where the GPS receiver downloads almanac
data before establishing a position fix.
CONTROL SEGMENT
A worldwide chain of monitoring and control stations that control
and manage the GPS satellite constellation.
COORDINATE
A set of numbers that describes your location on or above the
earth. Coordinates are typically based on latitude/longitude
lines of reference or a global/regional grid projection (e.g.,
UTM, MGRS, Maidenhead).
COORDINATED UNIVERSAL TIME (UTC)
Replaced Greenwich Mean Time (GMT) as the world standard for time
in 1986. It is based on atomic measurements rather than the
rotation of the earth. Greenwich Mean Time (GMT) is still the
standard time zone for the prime meridian (zero longitude).
COURSE
The direction from the beginning landmark of a course to its
destination (measured in degrees, radians, or mils) or the
direction from a route waypoint to the next waypoint in the route
segment.
COURSE DEVIATION INDICATOR (CDI)
A technique for displaying the amount and direction of crosstrack
error (XTE).
COURSE MADE GOOD (CMG)
The bearing from the 'active from' position (your starting point)
to your present position.
COURSE OVER GROUND (COG)
Your direction of movement relative to a ground position.
COURSE TO STEER
The heading you need to maintain in order to reach a destination.
CROSSTRACK ERROR (XTE/XTK)
The distance you are off the desired course in either direction.
D - F
DATUM
A math model which depicts a part of the surface of the earth.
Latitude and longitude lines on a paper map are referenced to a
specific map datum. The map datum selected on a GPS receiver
needs to match the datum listed on the corresponding paper map in
order for the position readings to match.
DEPTH CONTROLLED GAIN (DCG®)
A GARMIN proprietary technology that automatically adjusts
fishfinder sensitivity according to depth, not echo intensity.
The result is a much more detailed and accurate picture of bottom
structure.
DESIRED TRACK (DTK)
The compass course between the "from" and "to"
waypoints.
DIFFERENTIAL GPS (DGPS)
An extension of the GPS system that uses land-based radio beacons
to transmit position corrections to GPS receivers. DGPS reduces
the effect of selective availability, propagation delay, etc. and
can improve position accuracy to better than 10 meters.
DILUTION OF PRECISION (DOP)
A measure of the GPS receiver-satellite geometry. A low DOP value
indicates better relative geometry and correspondingly higher
accuracy. The DOP indicators are GDOP (geometric DOP), PDOP (position
DOP), HDOP (horizontal DOP), VDOP (vertical DOP), and TDOP (time
clock offset).
DISTANCE
The length (in feet, meters, miles, etc.) between two waypoints
or from your current position to a destination waypoint. This
length can be measured in straight line (rhumb line) or great
circle (over the earth) terms. GPS normally uses great circle
calculations for distance and desired track.
DOD
The U.S. Department of Defense. The DOD manages and controls the
Global Positioning System.
DOWNLINK
A transmission path for the communication of signals and data
from a communications satellite or other space vehicle to the
earth.
ELEVATION
The distance above or below mean sea level.
ELLIPSOID
A geometric surface, all of whose plane sections are either
ellipses or circles.
EPHEMERIS DATA
Current satellite position and timing information transmitted as
part of the satellite data message. A set of ephemeris data is
valid for several hours.
ESTIMATED POSITION ERROR (EPE)
A measurement of horizontal position error in feet or meters
based upon a variety of factors including DOP and satellite
signal quality.
ESTIMATED TIME ENROUTE (ETE)
The time it will take to reach your destination (in hours/minutes
or minutes/seconds) based upon your present position, speed and
course.
ESTIMATED TIME OF ARRIVAL (ETA)
The estimated time you will arrive at a destination.
FREQUENCY
The number of repetitions per unit time of a complete waveform,
as of a radio wave (see L1 and L2 frequencies in this glossary).
G - M
GEOCACHING
A high-tech version of hide-and-seek. Geocachers seek out hidden
treasures utilizing GPS coordinates posted on the Internet by
those hiding the cache.
GEODETIC DATUM
A math model representing the size and shape of the earth (or a
portion of it).
GEOGRAPHIC INFORMATION SYSTEM (GIS)
A computer system or software capable of assembling, storing,
manipulating and displaying geographically referenced information
(i.e., data identified according to their location). In practical
use, GIS often refers to the computer system, software and the
data collection equipment, personnel, and actual data.
GEOSYNCHRONOUS ORBIT
A specific orbit around where a satellite rotates around the
earth at the same rotational speed as the earth. A satellite
rotating in geosynchronous orbit appears to remain stationary
when viewed from a point on or near the equator. It is also
referred to as a geostationary orbit.
GLOBAL POSITIONING SYSTEM
A global navigation system based on 24 or more satellites
orbiting the earth at an altitude of 12,000 statue miles and
providing very precise, worldwide positioning and navigation
information 24 hours a day, in any weather. Also called the
NAVSTAR system.
GLONASS
The Russian Global Positioning System.
GOTO
A route consisting of one leg with your present position being
the start of the route and a single defined waypoint as the
destination.
GREENWICH MEAN TIME
The mean solar time for the meridian at Greenwich, England, used
as a basis for calculating time throughout most of the world.
Also called coordinated universal time.
GRID
A pattern of regularly spaced horizontal and vertical lines
forming square zones on a map used as a reference for
establishing points. Grid examples are UTM, MGRS, and Maidenhead.
HEADING
The direction in which a vehicle is moving. For air and sea
operations, this may differ from actual COG due to winds,
currents, etc.
HEALTHY
A term used when an orbiting GPS satellite is suitable for use.
I/O (INPUT/OUTPUT)
The two-way transfer of GPS information with another device, such
as a nav plotter, autopilot, or another GPS unit.
INITIALIZATION
The first time a GPS receiver orients itself to its current
location and collects almanac data. After initialization has
occurred, the receiver remembers its location and acquires a
position more quickly because it knows which satellites to look
for.
IONOSPHERE
A region of the earth's atmosphere where ionization caused by
incoming solar radiation affects the transmission of GPS radio
waves. It extends from a height of 50 kilometers (30 miles) to
400 kilometers (250 miles) above the surface.
INVERT ROUTE
To display and navigate a route from end to beginning for
purposes of returning to the route's starting point.
L1 FREQUENCY
One of the two radio frequencies transmitted by the GPS
satellites. This frequency carries the Coarse Acquisition Code (C/A
code), P-Code, and the nav message and is transmitted on a
frequency of 1575.42 MHz.
L2 FREQUENCY
One of the two radio frequencies transmitted by the GPS
satellites. This frequency carries only the P-Code, and is
transmitted on a frequency of 1227.6 MHz.
L-BAND
The radio frequencies that extend from 390 MHz to 1550 MHz. The
GPS carrier frequencies are in the L band (1227.6 MHz and 1575.42
MHz).
LATITUDE
A position's distance north or south of the equator measured by
degrees from zero to 90. One minute of latitude equals one
nautical mile.
LEG (ROUTE)
A portion of a route consisting of a starting (from) waypoint and
a destination (to) waypoint. A route that is comprised of
waypoints A, B, C, and D would contain three legs. The route legs
would be from A to B, from B to C, and from C to D.
LITHIUM BATTERY
A soft, silvery, highly reactive metallic element that is used in
batteries where weight and cold weather conditions are concerns.
LINE OF SIGHT PROPAGATION
Of an electromagnetic wave, propagation in which the direct
transmission path from the transmitter to the receiver is
unobstructed. The need for LOS propagation is most critical at
GPS frequencies.
LIQUID CRYSTAL DISPLAY (LCD)
A display circuit characterized by a liquid crystal element
sandwiched between two glass panels. Characters are produced by
applying an electric field to liquid crystal molecules and
arranging them to act as light filters.
LOCAL AREA AUGMENTATION SYSTEM (LAAS)
The implementation of ground-based DGPS to support aircraft
landings in a local area (20 mile range).
LONGITUDE
The distance east or west of the prime meridian (measured in
degrees), which runs from the north to south pole through
Greenwich, England.
LORAN
Loran, which stands for LOng RAnge Navigation, is a grid of radio
waves in many areas of the globe that allows accurate position
plotting. Loran transmitting stationsaround the globe continually
transmit 100 kilohertz radio signals. Special shipboard Loran
receivers interpret these signals and provide readings that
correspond to a grid overprinted on nautical charts. By comparing
signals from two different stations, the mariner uses the grid to
determine the position of the vessel.
MAGNETIC NORTH
Represents the direction of the north magnetic pole from the
observer's position. The direction a compass points.
MAGNETIC VARIATION
In navigation, at a given place and time, the horizontal angle (or
difference) between true north and magnetic north. Magnetic
variation is measured east or west of true north.
MAP DISPLAY
A graphic representation of a geographic area and the features in
it.
MEAN SEA LEVEL
The average level of the ocean's surface, as measured by the
level halfway between mean high and low tide. Used as a standard
in determining land elevation or sea depths.
MULTIPATH ERROR
An error caused when a satellite signal reaches the GPS receiver
antenna by more than one path. Usually caused by one or more
paths being bounced or reflected. The TV equivalent of multipath
is "ghosting."
MULTIPLEXING RECEIVER
A GPS receiver that switches at a very rapid rate between
satellites being tracked. Typically, multiplexing receivers
require more time for satellite acquisition, and are not as
accurate as parallel channel receivers. Multiplexing receivers
are also more prone to lose a satellite fix in dense woods than
parallel channel GPS receivers.
N - S
NAUTICAL MILE
A unit of length used in sea and air navigation, based on the
length of one minute of arc of a great circle, especially an
international and U.S. unit equal to 1,852 meters (about 6,076
feet).
NAVIGATION
The act of determining the course or heading of movement. This
movement could be for a plane, ship, automobile, person on foot,
or any other similar means.
NAVIGATION MESSAGE
The message transmitted by each GPS satellite containing system
time, clock correction parameters, ionospheric delay model
parameters, and the satellite’s ephemeris data and health.
The information is used to process GPS signals to give the user
time, position, and velocity. Also known as the data message.
NAVSTAR
The official U.S. Government name given to the GPS satellite
system. NAVSTAR is an acronym for NAVigation Satellite Timing and
Ranging.
NMEA (NATIONAL MARINE ELECTRONICS ASSOCIATION)
A U.S. standards committee that defines data message structure,
contents, and protocols to allow the GPS receiver to communicate
with other pieces of electronic equipment aboard ships.
NMEA STANDARD
A NMEA standard defines an electrical interface and data protocol
for communications between marine instrumentation.
NORTH-UP DISPLAY
A GPS receiver’s map display with north always fixed at the
top of the screen.
PARALLEL CHANNEL RECEIVER
A continuous tracking receiver using multiple receiver circuits
to track more than one satellite simultaneously.
P-CODE
The precise code of the GPS signal typically used only by the U.S.
military. It is encrypted and reset every seven days to prevent
use from unauthorized persons.
PIXEL
A single display element on an LCD screen. The more pixels, the
higher the resolution and definition.
POSITION
An exact, unique location based on a geographic coordinate system.
POSITION FIX
The GPS receiver's computed position coordinates.
POSITION FORMAT
The way in which the GPS receiver's position will be displayed on
the screen. Commonly displayed as latitude/longitude in degrees
and minutes, with options for degrees, minutes and seconds,
degrees only, or one of several grid formats.
PRIME MERIDIAN
The zero meridian, used as a reference line from which longitude
east and west is measured. It passes through Greenwich, England.
PSEUDO-RANDOM CODE
The identifying signature signal transmitted by each GPS
satellite and mirrored by the GPS receiver in order to separate
and retrieve the signal from background noise.
PSEUDORANGE
The measured distance between the GPS receiver and the GPS
satellite using uncorrected time comparisons from satellite
transmitted code and the local receiver's reference code.
QUADRIFILAR HELIX ANTENNA
A type of GPS antenna in which four spiraling elements form the
receiving surface of the antenna. For GPS use, quadrifilar
antennas are typically half-wavelength or quarter-wavelength size
and encased in a plastic cylinder for durability.
RS-232
A serial input/output standard that allows for compatibility
between data communication equipment made by various
manufacturers.
RADIO TECHNICAL COMMISSION FOR MARITIME SERVICES (RTCM)
SPECIAL COMMITTEE 104
A committee established for the purposes of establishing
standards and guidance for interfacing between radiobeacon-based
data links and GPS receivers, and to provide standards for ground-based
differential GPS stations.
RAIM
Receiver Autonomous Integrity Monitoring - A GPS receiver system
that would allow the receiver to detect incorrect signals being
transmitted by the satellites by comparing solutions with
different sets of satellites.
ROUTE
A group of waypoints entered into the GPS receiver in the
sequence you desire to navigate them.
SEARCH THE SKY
A message shown when a GPS receiver is gathering satellite
almanac data. This data tells the GPS receiver where to look for
each GPS satellite.
SERIAL COMMUNICATION
The sequential transmission of the signal elements of a group
representing a character or other entity of data. The characters
are transmitted in a sequence over a single line, rather than
simultaneously over two or more lines, as in parallel
transmission. The sequential elements may be transmitted with or
without interruption.
SEE-THRU® TECHNOLOGY
A GARMIN exclusive technology which allows the various GARMIN
fishfinders to hear both weak and strong signals simultaneously
so as to identify fish returns under the toughest conditions:
suspended in thermoclines or even hiding near structures.
SELECTIVE AVAILABILITY (SA)
The random error, which the government can intentionally add to
GPS signals, so that their accuracy for civilian use is degraded.
SA is not currently in use.
SONAR
A system using transmitted and reflected underwater sound waves
to detect and locate submerged objects or measure the distance to
the floor of a body of water. The technology used in GARMIN
fishfinders and sounder products.
SPACE SEGMENT
The satellite portion of the complete GPS system.
SPEED OVER GROUND (SOG)
The actual speed the GPS unit is moving over the ground. This may
differ from airspeed or nautical speed due to such things as head
winds or sea conditions. For example, a plane that is going 120
knots into a 10-knot head wind will have a SOG of 110 knots.
SPREAD SPECTRUM
The received GPS signal is wide bandwidth and low power. The L-band
signal is modulated with a pseudo random noise code to spread the
signal energy over a much wider bandwidth than the signal
information bandwidth. This provides the ability to receive all
satellites unambiguously and to give some resistance to noise and
multipath.
STATUTE MILE
A unit of length equal to 5,280 feet or 1,760 yards (1,609 meters)
used in the U.S. and some other English-speaking countries.
STRAIGHT LINE NAVIGATION
The act of going from one waypoint to another in the most direct
line and with no turns.
T - Z
TIME TO FIRST FIX (TTFF)
If you have not used your GPS unit for several months, the
almanac data for the satellites may be out of date. The unit is
capable of recollecting this information on its own, but the
process can take several minutes. The time it takes after the
user first turns on the GPS receiver, when a GPS receiver has
lost memory, or has been moved over 300 miles from its last
location. The time it takes to find the satellites is called the
Time to First Fix (TTFF).
TracBack®
The proprietary GARMIN feature which takes your current track log
and converts it into a route to guide you back to a starting
position.
TRACK-UP DISPLAY
The GPS receiver’s map display with the current direction of
travel at the top of the screen. The map display will rotate as
you make turns to keep your track at the top of the screen.
TRACK (TRK)
Your current direction of travel relative to a ground position (same
as Course Over Ground).
TRANSDUCER
A device, much like a microphone, that converts input energy of
one form into output energy of another. Fishfinders separate and
enhance the information received from a transducer to show
underwater objects.
TRIANGULATION
A method of determining the location of an unknown point, as in
GPS navigation, by using the laws of plane trigonometry.
TROPOSPHERE
The lowest region of the atmosphere between the surface of the
earth and the tropopause, characterized by decreasing temperature
with increasing altitude. GPS signals travel through the
troposphere (and other atmospheric layers).
TRUE NORTH
The direction of the north pole from your current position.
Magnetic compasses indicate north differently due to the
variation between true north and magnetic north. A GPS receiver
can display headings referenced to true north or magnetic north.
TURN (TRN)
The degrees which must be added to or subtracted from the current
heading to reach the course to the intended waypoint.
UNIVERSAL TIME COORDINATED (UTC)
A universal time standard, referencing the time at Greenwich,
England. Also referred to as GMT or Zulu time.
UNIVERSAL TRANSVERSE MERCATOR (UTM)
A nearly worldwide coordinate projection system using north and
east distance measurements from reference point(s). UTM is the
primary coordinate system used on U.S. Geological Survey
topographic maps.
UPLINK
A transmission path by which radio or other signals are sent from
the ground to an aircraft or a communications satellite.
USER INTERFACE
The way in which information is exchanged between the GPS
receiver and the user. This takes place through the screen
display and buttons on the unit.
USER SEGMENT
The segment of the complete GPS system that includes the GPS
receiver and operator.
VELOCITY MADE GOOD (VMG)
The rate of closure to a destination, based upon your current
speed and course.
WAVELENGTH
The distance between points of corresponding phase of two
consecutive cycles of a wave.
WAYPOINTS
Waypoints are locations or landmarks worth recording and storing
in your GPS. These are locations you may later want to return to.
They may be check points on a route or significant ground
features. (e.g., camp, the truck, a fork in a trail, or a
favorite fishing spot). Waypoints may be defined and stored in
the unit manually, by taking coordinates for the waypoint from a
map or other reference. This can be done before ever leaving home.
Or more usually, waypoints may be entered directly by taking a
reading with the unit at the location itself, giving it a name,
and then saving the point. Waypoints may also be put into the
unit by referencing another waypoint already stored, giving the
reference waypoint, and entering the distance and compass bearing
to the new waypoint.
WIDE AREA AUGMENTATION SYSTEM (WAAS)
A system of satellites and ground stations that provide GPS
signal corrections for better position accuracy. A WAAS-capable
receiver can give you a position accuracy of better than three
meters, 95 percent of the time. WAAS consists of approximately 25
ground reference stations positioned across the United States
that monitor GPS satellite data. Two master stations, located on
either coast, collect data from the reference stations and create
a GPS correction message. This correction accounts for GPS
satellite orbit and clock drift plus signal delays caused by the
atmosphere and ionosphere. The corrected differential message is
then broadcast through one of two geostationary satellites, or
satellites with a fixed position over the equator. The
information is compatible with the basic GPS signal structure,
which means any WAAS-enabled GPS receiver can read the signal.
WGS-84
World Geodetic System - 1984. The primary map datum used by GPS.
Secondary datums are computed as differences from the WGS 84
standard.
Y-CODE
The encrypted P-Code.
http://www.gpsworld.com/" GPS World Online - Keep up with what's going on in the fast-paced world of GPS
http://www.cgrer.uiowa.edu/servers/servers_references.html - Maps, Maps, From the University of Iowa Center for Global & Regional Environmental Research.
http://www.gorp.com/ Great Outdoor Recreation Page - Great source for recreation information in state & national parks.
http://www.gearhead.com/ Gearhead Cyberzine - A cyberzine for mountain bikers.
http://www-personal.umich.edu/~tmorris/index.htm Best Boating Resources on the Web If it floats and it's on the web, it's here.
http://www.afn.org/~afn05660/aviation.html Aviation Links - Alan and Dawn Brue have compiled a long list of interesting sites for web pilots.
Find a dealer near you at http://www.garmin.com/dealers/ (some sell on online).
GARMIN's Limited Warranty Policy warrants all products to be free from defects in materials and workmanship for one year from the date of purchase.
GARMIN supports its dealer network by selling units through dealers only. For accessories contact [email protected] or call the Customer Service Department at 1-800-800-1020
A list of Dealers in Columbia, SC is at http://www.garmin.com/cgi-bin/us_dealers?state=SC&city=Columbia
Best Buy #264 (10-9PM M-S)
370 Harbison Blvd
Columbia, SC 29212
Phone: 803 749 2188
Fax: Mobile Electronics
Best Buy #270
7006 Two Notch Rd
Columbia, SC 29223
Phone: 803 736 2529
Fax: Mobile Electronics
Boater's World #631
1009 Bower Pkwy
Columbiana Station, Columbia
Columbia, SC 29212
Phone: 803 732 2300
E-mail: [email protected]
Website: http://www.boatersworld.com Marine
Recreational
Dick's Sporting Goods Inc.
1110 Bower Parkway
Columbia, SC 29210
Phone: 803 749 0756
E-mail: [email protected]
Website: http://www.dickssportinggoods.com/searchHandler/index.jsp?searchld=74391563&keywords=garmin
Recreational
Wal-Mart
360 Harbison Blvd
Columbia, SC 29212
Phone: (803)781-0762
Website: http://www.walmart.com/reflect.gsp?adid=0100000016180412704738&dest=1788
Recreational
Wal-Mart
7501A Garner Ferry R
Columbia, SC 29209
Phone: (803)783-1277
Website: http://www.walmart.com/reflect.gsp?adid=0100000016180412704738&dest=1788
Recreational
Wal-Mart
9710 Two Notch Road
Columbia, SC 29223
Phone: (803)736-8123
Website: http://www.walmart.com/reflect.gsp?adid=0100000016180412704738&dest=1788
Recreational
Wal-Mart
5420 Forest Drive
Columbia, SC 29206
Phone: (803)782-0323
Website: http://www.walmart.com/reflect.gsp?adid=0100000016180412704738&dest=1788
Recreational
West Marine Products (10-6PM M-S)
Dutch Square Center #98
Columbia, SC 29210
Phone: 803 750 5034
Website: http://www.westmarine.com
Wal-Mart
5556 Sunset Blvd
Lexington, SC 29072
Phone: (803)957-4481
Website: http://www.walmart.com/reflect.gsp?adid=0100000016180412704738&dest=1788
Reproduction without permission of a detailed 70 page instruction manual for this model (Part # 190-00193-00-Rev. D , February 2001, printed in Taiwan) is forbidden. For $14, one can be ordered from GARMIN International Inc. at 1200 E. 151st Street Olathe, KS 66062 (Kansas City metro area) Phone: (913) 397-8200 FAX: (913) 397-8282) or at [email protected] ?
Contact Garmen Customer Service Department at 1-800-800-1020 M-F 8-5 CST (GMT -6:00). A Technical Support e-mail form is at http://www.garmin.com/contactUs/techSupport.html
Files gps4beg.pdf (a 524K GPS Guide for Beginners) and etrex_sum.pdf (a 1.4MB eTrex Summit User's Manual) can be downloaded from http://www.garmin.com/support/userManual.html . A free version of Adobe Acrobat Reader which can read and PRINT A HARD COPY of these files can be downloaded from http://www.adobe.com/products/acrobat/readstep2.html
The GPS receivers described below can not receive WAAS signals, which might make them OBSOLETE.
To upgrade eTrex GPS receiver software select your model at http://www.garmin.com/outdoor/products.html , and then the upgrade software download page.
Most of the information below came from: http://www.garmin.com/products/etrex/
The $267 eTrex Summit has a Built-In Electronic Compass, a Built-In Barometric Altimeter, more Routes / # of waypoints per route (1/50 vs 20/50) and more # of Tracklog Points (1536 vs 3000) than the $145 eTrex.
The screens shown by this model are at http://www.garmin.com/products/etrexsummit/screen.html
The latest production software as of 10/11/01 for eTrex Summit is version 2.10, which can be downloaded at http://www.garmin.com/products/etrexsummit/download.html (cables, etc. required).
Waypoints/Icons: 500 with name and graphic symbol
Tracks: Automatic track log; 10 saved tracks let you retrace your path in both directions
Route: 20 reversible routes with up to 50 waypoints (available only by the free update offered on the eTrex website)
Trip computer: Current speed, average speed, time of sunrise/sunset, resetable maximum speed, trip timer, and trip distance
Map datums: More than 100
Position format: Lat/Lon, UTM/UPS, Maidenhead, MGRS and other grids
Electronic compass features
Accuracy: ±5 degrees with proper calibration (user calibration)
Resolution: 1 degree
Barometric altimeter features
Accuracy: 10 feet with proper calibration (user and/or automatic calibration)
Resolution: 1 foot
Range: -2,000 to 30,000 feet
Elevation computer: Current elevation, resetable minimum and maximum elevation, ascent/descent rate, total ascent/descent, average and maximum ascent/descent rate
Pressure: Local pressure (mbar/inches HG), 12-hour automatic pressure trend recording
Receiver: Differential-ready, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position
Acquisition Times:
Warm: approx. 15 seconds
Cold: approx. 45 seconds
AutoLocate™: approx. 5 minutes
Update Rate: 1 second, continuous
Accuracy:
Position: 15 meters (49 feet) RMS
Velocity: 0.1 knot RMS steady state
Dynamics: 6g's
Interfaces: RS232 with NMEA 0183, RTCM 104 DGPS data format and proprietary GARMIN
Antenna: Built-in patch
Size: 4.4"H x 2.0"W x 1.2"D (11.2 x 5.1 x 3.0 cm)
Weight: 5.3 ounces (150 g) with batteries
Display: 2.1"H x 1.1"W (5.4 x 2.7 cm) high-contrast LCD with bright backlighting
Case: Waterproof to IEC 529 IPX7 standards
Temperature range: 5°F to 158°F (-15°C to 70°C)
Data storage: Indefinite; no memory battery required
Source: 2 AA batteries (not included)
Battery Life: Up to 16 hours (typical use)
The basic etrex costs $145.00 (it can not receive WAAS signals).
NAVIGATION FEATURES
Waypoints/Icons: 500 with name and graphic symbol
Tracks: Automatic track log; 10 saved tracks let you retrace your path in both directions
Route: 1 reversible route with up to 50 waypoints
Trip computer: Current speed, average speed, time of sunrise/sunset, resetable maximum speed, trip timer, and trip distance
Map datums: More than 100
Position format: Lat/Lon, UTM/UPS, Maidenhead, MGRS and other grids
PERFORMANCE
Receiver: Differential-ready, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position
Acquisition Times:
Warm: approx. 15 seconds
Cold: approx. 45 seconds
AutoLocate: approx. 5 minutes
Update Rate: 1 second, continuous
Accuracy:
Position: 15 meters (49 feet) RMS*
* Subject to accuracy degradation to 100m 2DRMS under the United
States Department of Defense-imposed Selective Availability
Program.
Velocity: 0.1 knot RMS steady state
Dynamics: 6g's
Interfaces: RS232 with NMEA 0183, RTCM 104 DGPS data format and proprietary GARMIN
Antenna: Built-in patch
PHYSICAL
Size: 4.4"H x 2.0"W x 1.2"D (11.2 x 5.1 x 3.0 cm)
Weight: 5.3 ounces (150 g) with batteries
Display: 2.1"H x 1.1"W (5.4 x 2.7 cm) high-contrast LCD with bright backlighting
Case: Waterproof to IEC 529 IPX7 standards
Temperature range: 5°F to 158°F (-15°C to 70°C)
Data storage: Indefinite; no memory battery required
POWER
Source: 2 AA batteries (not included)
Battery Life: Up to 22 hours
The information below is from http://www.garmin.com/support/faqs/faq.html
:
The following is a listing of Frequently Asked Questions and
responses which are often encountered by our Technical Support
Group.
General GPS Information:
Q. How accurate is a GARMIN GPS?
A. With the end of Selective Availability, you can expect
horizontal accuracy of 20m to 35m (60' to 105') for older 8
channel units and 7m to 15m (21' to 45') for newer 12 parallel
channel units in good reception conditions. For altitude you can
expect accuracy to range from +/- 75m (225') for an 8 channel
unit and +/- 35m (105') for 12 parallel channel units in good
reception conditions. There are a number of environmental
conditions that can affect GPS accuracy due to varying satellite
signal reception conditions and can therefore lead to better or
worse accuracy's than listed above. The satellite status page on
most GARMIN GPS units will provide a real-time estimate of the
relative accuracy of the position reported by the GPS receiver.
Q. Can I post-process the data collected with my GARMIN GPS unit
to obtain greater accuracy?
A. Unfortunately not. GARMIN GPS units and other handheld
consumer-grade units do not internally store the raw pseudorange
data from the satellites required to post-process differential
corrections. This type of capability is only found in survey-grade
GPS equipment.
GPS Operations/Features:
Q. Do I need to remove the batteries from my GARMIN handheld GPS
unit when I connect the unit to the 12 vdc battery on my boat or
car?
A. No. When the unit detects that external power is available,
the unit will automatically switch to the external source and not
use the batteries in the unit. It is recommended that the
batteries remain in the unit in the event that you have a loss of
battery power. If the batteries remain in the unit, when external
power is lost the unit will automatically switch to batteries and
continue to function normally.
Q. What is a Waypoint?
A. Waypoints are locations or landmarks worth recording and
storing in your GPS. These are locations you may later want to
return to. They may be check points on a route or significant
ground features. (e.g., camp, the truck, a fork in a trail, or a
favorite fishing spot).
Waypoints may be defined and stored in the unit manually, by
taking coordinates for the waypoint from a map or other reference.
This can be done before ever leaving home. Or more usually,
waypoints may be entered directly by taking a reading with the
unit at the location itself, giving it a name, and then saving
the point.
Waypoints may also be put into the unit by referencing another
waypoint already stored, giving the reference waypoint, and
entering the distance and compass bearing to the new waypoint.
Q. What is a Route?
A. A route is a series of waypoints entered in the order that you
want to navigate them.
Q. What is a Track Log?
A. The track log in a GARMIN unit are points automatically stored
when you are moving. It is the electronic equivalent of laying
down a "breadcrumb trail" to mark your path. These
points will be shown strung together on the map page of your unit
so you can see where you have been.
Q. What is TracBack?
A. TracBack is a feature which allows you to return along a
traveled path or route without marking any waypoints. The GPS
unit will store a tracklog or "electronic breadcrumb trail"
as you travel. When you are ready to return to where you started,
the GPS unit will look at the hundreds or thousands of tracklog
points and take the 30 most significant and turn them into a
route to lead you back to your starting point.
Q. How do I scroll through my waypoints when entering waypoints
into a route?
A. If you have multiple waypoints with the same first character(s)
you will have to move the cursor to the second digit and continue
to spell the waypoint identifier in order to continue to scroll
through the list.
Q. What GARMIN units feature Military Grid Reference System (MGRS)?
A. Among others, the GPS 12, GPS 12XL, GPS 48, GPS 92, GPS 126,
GPS 128, GPSMAP 295, eMap, eTrex, GPS III Plus, GPS 12Map, GPS 76,
GPSMAP 76, GPSMAP 176, GPSMAP 176C, and GPS V support the MGRS
coordinate system.
WAAS:
Q. What is WAAS?
A. WAAS stands for the "Wide Area Augmentation System".
The Wide Area Augmentation System (WAAS) is an FAA funded project
to improve the overall accuracy and integrity of the GPS signal
for flying in instrument meteorological conditions, primarily
during the approach to landing phase of flight. It is a space-based
system that broadcasts integrity information and correction data
as determined by ground reference stations. At this time the
system is still in the development stage with a goal of providing
reliable signals with an accuracy of 7 meters (21-22ft) both
horizontally and vertically 95+% of the time. Current tests have
shown the actual accuracy to be on the order of 2-3 meters. For
more information, go to http://gps.faa.gov/Programs/WAAS/waas.htm.
Q. I'm trying to use WAAS on my eTrex Venture/Legend/Vista but
I'm not able to obtain a differential position. What could be
wrong?
A. There are three items to look at:
(1) Ensure that you have enabled the WAAS mode in the System
screen of the Main Menu.
(2) Depending on your location, you may not have a good line of
sight to the required WAAS satellite which will make signal
reception very difficult.
(3) You may not have collected enough information from the WAAS
satellite. (See below for details.)
Detail:
(1) Please refer to your Owner's Manual for instructions on
enabling the WAAS feature.
(2) There are currently two WAAS satellites that can be received
in the United States. One is over the Atlantic Ocean and one is
over the Pacific Ocean. The satellites are in a geo-stationary
orbit over the equator, so the farther north you are, the greater
the difficulty in picking up the signal. These factors put the
satellites very close to the visible horizon, allowing the signal
to be blocked by terrain or buildings (the WAAS signal is in the
same frequency range as the GPS signal and is a line of sight
transmission). The best results using WAAS with the eTrex Venture/Legend/Vista
units will occur by literally "pointing" the patch
antenna of the unit at the location of the satellite. You can
determine this by looking for satellites 35 (East Coast) and 47(West
Coast) on the Satellite Status page in your GPS unit.
(3) You will need to allow the unit to have good visibility of
the WAAS satellites and track the signal for 10-20 minutes. After
the initial data collection takes place, the unit will be able to
quickly acquire the WAAS satellites and will normally take about
1-2 minutes to obtain a differential position fix. For more
information on how to read the satellite status page, please
refer to the appropriate owner's manual for your GPS.
Warranty/Repairs:
GARMIN's technical support department is available M-F, 8:00-5:00
Central Time (except holidays).
When you call technical support, please have available the serial
number of the unit, your return shipping address and a daytime
telephone number. A technical support specialist will provide you
with a Return Material Authorization tracking number (RMA#) and
shipping instructions.
Once you have received the RMA number, ship the unit (insured) to
the following address:
GARMIN International
ATTN: RMA #
1200 E. 151st Street
Olathe, KS 66062 USA
Common Troubleshooting Questions:
Q. What do I do when my unit displays a "Low Memory Battery"
message?
A. If you have a cigarette lighter adapter cable or a power data
cable, plug the unit into a power source for 3 days (car, boat,
etc.) to recharge the internal memory battery. If you do not have
a cable, place a fresh set of AA batteries in the unit and leave
the unit powered off for approximately 5 days to recharge the
internal memory battery. Once the internal memory battery is
recharged, the "Low Memory Battery" message should no
longer be displayed.
If the message persists, it will be necessary to return the GPS
unit to GARMIN so the internal memory battery can be replaced. If
this is the case, please send us a Technical Support email
<http://www.garmin.com/contactUs/techSupport.html>. A
Return Material Authorization (RMA) will be set up and returned
to you via e-mail with shipping instructions. The RMA number will
ensure accurate tracking and prompt return of the unit to you.
If you own an 8-channel GPS receiver unit, a marine GPS unit or
chartplotter, or an aviation handheld, your unit has a non-rechargeable
memory battery. You will also need to send your unit to GARMIN
for replacement under our flat-rate repair program. In this case,
please email GARMIN using the above link or call GARMIN Product
Support at 1-800-800-1020 to arrange for an RMA number to be
issued for the return of your unit.
As memory technology has advanced, many GARMIN GPS units (from
1999 on) no longer require a memory battery to support user data.
Q. I just turned on my GPS today and it will not acquire
satellites. What should I do?
NOTE: Most of GARMIN's newer 12 parallel channel GPS receivers do
not require special steps when the unit has been in extended
storage. Simply turn the unit on and let it lock onto the
satellites.