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Today's Star-Buy satellite navigation system is...
...a TOM TOM one - V4 GB SAT NAV SYSTEM. |
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Plug & Go: Works straight out of the box. High quality touchscreen (320 x 240 pixels, 64.000 colors) High res graphics and choice of routes: such as shortest, avoiding toll roads etc. Postcode Navigation: for simple and accurate selection of your destination. Clear spoken instructions in your own language (36 languages to choose from) |  |
With FREE DELIVERY + 1 Year Parts/Labour Guarantee. |
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A beginner's guide to buying GPS - answering some frequently asked questions.
Read the helpful hints and facts below before buying your satellite navigation system or satellite navigation system accessory.
Are they really that useful, and do I really want one?What would I use it for?
Help me with the options. . .
1. In-Car
· 1.1 Component based systems
· 1.2 PDA based solutions
So what is Bluetooth?
· 1. Tracking units / Dataloggers
· 2. Recreational units
· 3. Motorbike based systems
So how do I decide what to buy?
What is the Global Positioning System?
What is a GPS receiver?
Are there many different types of GPS receiver?
What is the level of accuracy?
What is the safety aspect for long distance walkers?
What specification should I go for when long distance walking?
Does a GPS make my faithful maps and compass redundant?
What is the difference between 'routes' and 'tracks'?
Will the system work indoors?
What type of batteries should be used in a GPS?
Can I expect my GPS to be waterproof?
Plus an A to Z glossary of GPS and sat-nav terms.
Are they really that useful, and do I really want one?
An important question to ask yourself very early on when thinking Sat-Nav GPS, the following information will help you to understand different applications and models of GPS systems.
So what is the answer?
There may not be a single answer, but then again, there may be several,
- I am a serious walker or climber
- I regularly travel on business
- I'm off on a touring holiday
- I've bought a new boat
- I'm hopeless with directions
- all of my mates have got one . . .
- . . . and so on and so on
There is a multitude of uses for GPS devices and it really is a wonder everyone hasn't got one already. One thing is for sure, once it becomes a part of your life you will wonder how you ever got around without it.
What would I use it for?
The fundamental use of the GPS / Sat-Nav device is to utilise the Global Positioning System (GPS) satellites to determine an exact position at any given moment in time. Acting as a decoder for data that it receives from Satellites orbiting above the Earth, the device translates the data and will tell you to within a few feet of exactly where you are positioned around the Globe at any given time.
One obvious use is for walkers and climbers who can use a GPS system to determine their exact geographical whereabouts. They can then log their position into the device and by use of a compass return to that same spot with a high degree of accuracy at any time they choose. It's worth noting that a number of GPS systems have a built in compass, some even have a built in barometric altimeter!
Drivers can use mapping and navigation software. By "informing" the device of the location of their desired destination the software within the device is utilised to calculate the shortest route and then guide the driver there by use of either voice or visual commands.
Sports persons can determine their speed and direction as their GPS system measures the time taken to travel between points and utilises software to make the calculations.
Golfers, can determine exactly where they are on a hole relative to the centre of the green or some other pre-programmed point. (Navigational devices are banned in Golfing Competitions)
And so it goes on, the GPS unit determines the current position and the application software stores that information and uses it to make calculations that in turn deliver information in a format useful to you.
Help me with the options. . .
There is a major decision that needs to be taken early on when deciding to purchase a navigational device otherwise the choices can be mind boggling. It really revolves around the hardware and software options and the type of use you have in mind for the device. Some of the choices you are presented with are:
1. In-Car
This is the GPS solution for anyone wanting to find his or her way from A-to-B using the road network.
In-Car Satellite Navigation (Sat-Nav) systems can be further explained in the following sub-categories: -
1.1 Component based systems
Transferable or dedicated devices are self-contained GPS units that can easily be moved from one vehicle to another. They are preloaded by the manufacturers with application software and are ready to use straight from the box.
The Navman iCN520 is a typical example of a transferable GPS system. Designed to be used in a vehicle, with its in-built GPS receiver the iCN520 attaches to the windscreen and is powered by a cigar lighter or an integrated rechargeable battery. UK mapping is pre-installed on it's memory card giving voice and visual turn-by-turn instructions for navigating anywhere in the UK.
For those who want to venture further afield European mapping is available as an optional accessory. Alternatively there are transferable units supplied with internal hard drives. The TomTomGO 540 live (portable) is an excellent example, It's one of the smartest portable car navigators with detailed maps of your region plus the major roads of Europe on SD card. Everything you need for navigating from A TO B is included. The TomTomGO 540 sits securely on its windscreen mount and offers both voice and on-screen turn-by-turn instructions. The TomTomGO 540 boasts some excellent extra features; it even acts as a Bluetooth 'hands-free' kit for compatible Bluetooth mobile phones and with a safety camera indicator allows you to get to your destination more safely by informing you of what the road ahead holds for you.
A lot of the more modern vehicles are now coming equipped with either a heated screen or a heat reflective screen. Unfortunately these can affect the GPS signal and in some instances block it all together. An external antenna is the answer, and if available we will have the correct option listed under the accessories tab for your chosen system, if you are unsure consult your dealer at time of purchase.
1.2 PDA based solutions
The need for navigation systems has encouraged massive growth in the Personal Digital Assistant (PDA) market as it has provided a cost effective equivalent to transferable solutions. Some people may already own a PDA and want to make further use of its excellent potential.
Why would I want a PDA based solution?
There are many answers to this question:-
- I want a specific type of GPS receiver
- I want to use specific mapping
- I want to make the most of my PDA
- I want as much flexibility as possible
- I want to use the system for multiple applications
So what is Bluetooth?
Bluetooth is a wireless technology that connects two devices allowing them to communicate with each other. Bluetooth devices need to be "paired" to allow continuous, secure communication. A Bluetooth wireless connection allows the GPS receiver to be placed up to 10 metres away from the paired device, sending information without any connecting cables.
1. Tracking units / Dataloggers
These units are designed for those people who need to keep an accurate trace on a vehicle or a person's whereabouts. They act as a regular GPS receiver and transmit their data to a PDA running the navigation software but they will also keep a record of the areas travelled during the day. This information can then be uploaded and shown on mapping software. There are a variety of systems on the market, Bluetooth units being the most common. Battery life and data storage capacity are key features to look for when choosing a unit.
2. Recreational units
There are various options for the user who requires a unit for recreational use. From the occasional walker to the hardened Rambler, there is an option to suit all. When choosing a unit there are some important features to consider. . .
- Do you require mapping capabilities?
- What sort of battery life do you require?
- Are you going to be connecting to a PC?
- Do you require additional electronic sensors?
- Is it a marine or a land-based unit you require?
3. Motorbike based sat nav systems
Bikers can also benefit from GPS technology. The key requirements for bikers are a waterproof unit, shock resistance and the available mapping options. Not many units will offer all that is required for on bike navigation however, Garmin offer two units that are suitable, the Garmin Quest and the Garmin Streetpilot 2610.
These units, via optional mounting accessories, have the advantage of being able to link into a riders existing intercom system so you can still receive voice guidance while you ride. The Quest is slightly limited as although it comes with full Western European mapping on CD-ROM it has a fixed internal memory that can accommodate approximately one country at a time. The 2610 relies on compact flash memory cards so various maps throughout Europe can be installed on a collection of cards.
Although there are systems that contain the entire European mapping on a hard drive they are not recommended due to the potential shock damage from a bike.
TomTom have a new system to compete with those from Garmin. The new Tom-Tom Rider has been specially designed for use on a motorbike and is a further step in the development of the TomTom GO range. The new Rider is fully waterproof and comes with a Bluetooth headset to receive voice commands. This is an ideal system for those requiring a full postcode search. The TomTom Rider even has a modified user interface so the controls can be operated with a gloved hand!
So how do I decide what to buy?
There's good and bad news here - The good news is that there is lots of choice and in many respects it's a bit like buying a camera or a car. Ask around, decide how much money you have to spend, decide what the principle reason for buying one is and research the various options.
The bad news, or is it really good news, is that you don't have to read through 20 different magazines before making a choice. That's mainly because there aren't 20 different magazines on the subject. There are some websites but with one or two notable exceptions they tend to be somewhat of a technical nature for the newbie.
Frequently Asked Questions
What is the Global Positioning System?
The Global Positioning System (GPS) is a group of twenty-four GPS satellites orbiting 12,000 miles above the earth and transmitting the exact time relevant to their exact position in space.
What is a GPS receiver?
A GPS receiver is a device located on the earths surface that is "tuned in" to signals transmitted from satellites. The device (Sat - Nav receiver) then descodes this information, detrmining the location; speed, altitude and heading of the device and displays it to the user.
Are there many different types of GPS receiver?
Yes several! Different chip-sets within individual units (devices) are what determine their accuracy. Models also differentiate themselves from each other in the way that they communicate their info to the user.
Some are integrated into a unit, some are wired and some are portable (hand-held).
What is the level of accuracy?
Since the relaxation of selective availability on the 2 May 2000, accuracy has been greatly increased to around 20 meters, while WAAS equipped receivers are able to achieve an accuracy of up to 7 meters. The GPS functions at up to 951mph or 999 knots - certainly adequate for most users!
What is the safety aspect for long distance walkers?
Sat-Nav devices have proven themselves an invaluable and life-saving addition to essential equipment carried by walkers, who can often find themselves in unfamiliar terrain in conditions of poor visibility or traversing hostile terrain. They can be especially useful in countries where the quality of local maps is of a poor standard. A more simple use is to guide the user from door to door in more familiar terrain, but using the shortest route possible as determined by the satellites orbiting above the Earth.
What specification should I go for when long distance walking?
If you find yourself in hostile terrain (mountainous or surrounded by forestry) you will want a model incorporating a 12-channel receiver so as to give you maximum confidence in the strength of the signal. Also many makes and models differ widely in battery life so check the specification carefully before making your purchase. If you are travelling long distances, the weight of the device will be a factor you must take into consideration. Ask before you buy; is it genuinely waterproof, or just showerproof (there is a big difference). Will you be travelling in darkness? If so you will want a device equipped with a backlight for the LCD screen.
Does a GPS make my faithful maps and compass redundant?
Nah! In the same way that you would keep a spare wheel and jack in the boot of your car, you should still make room for your tried and trusted friends; the map and compass. You will find that, as invaluable as your GPS - Sat-Nav device becomes to you as you get used to it, and as accurate as it will be (and it will be), it cannot contain detail that you will find on an area specific map. You would not embark upon a long road journey without a functioning spare wheel, so do not embark upon a (possibly hazardous) journey on foot without the back-up of your trusty map and compass, the latter of which, at low speeds or a standstill, will always be more accurate than your device which uses constant calculation to determine your exact location and can therefore be slightly off course at any given time.
What is the difference between 'routes' and 'tracks'?
You can preload your device with a series of named points (waypoints) along the distance of your intended journey. When strung together these waypoints become the Route. If you know of a place where refreshment and rest can be taken and you enter it into your device (maybe using a detailed map) it becomes a waypoint; it could also be anything from a distinguished landmark to a bend in a river. The location of points you have entered into the memory of your device then become your "guides" along the intended route. At the touch of a button your device can tell you which point you are at and the distance to be travelled to the next one.
As you travel along your journey your device makes a log of "points" of the journey. They're not as detailed as waypoints in that you do not refer to them as named navigational pointers these stored "points" of your journey make it possible for the device to trackback and reverse the journey that you have taken. So a journey taken into strange and unfamiliar territory can be embarked upon with a degree of added confidence knowing that your device is constantly mapping a possible return journey track for you.
Will the system work indoors?
Any signal showing on your device from inside a brick structure building should be treated as unreliable. The system works on the line of sight principle and generally has to be within the line of sight of the satellite from which it is receiving the data. The signal will carry successfully through clothing or tent canvas but brick and concrete impair its accuracy .
What type of batteries should be used in a GPS?
Your GPS device will run on various sources of power and battery models can run on Alkaline types, but for long life the best option is the more expensive Lithium type. You can typically expect to get a 30% increase in battery life by choosing Lithium over Alkaline. Rechargeable Nickel Cadmium (NiCad) batteries are an option but offer a comparatively poor return in longevity. As a rule of thumb, performance comparisons can be made along the lines of; NiCad 1 hour, Alkaline 3 hours, Lithium 4 hours. A fourth option; rechargeable NiMH batteries do offer longer life over rechargeable NiCad's but their expense, being considerably higher than the others, makes their use somewhat prohibitive.
Can I expect my GPS to be waterproof?
There are some excellent waterproof devices on the market (mainly sold in the marine sector) and if you are looking for a fully waterproof model then you must specify that when making your purchase. Some models can be sold as waterproof, which are in fact only splashproof or showerproof (not the same thing as waterproof at all) there are various levels of IEC529 certification for waterproofed models and this is the information you need to know:
- IPX8 - Fully waterproof
- IPX7 - waterproofed if dropped in water
- IPX4 - splash proof
- IPX2 - Certificated for mild exposure (fog or mist) to the weather
If you feel that there is scope for error here, do not go ahead and spend on a device that you may find unsuitable. The most comprehensive, unbiased advice that we can find for you online can be found here www.globalpositioningsystems.co.uk
A to Z Glossary of GPS Terms
A B C D E F G H I L M N P Q R S T U V W
Accuracy
The calculation of the distance between the GPS device reported position and the physical position of the device on the ground.
Acquisition Time
The time it takes a GPS receiver to acquire satellite signals, decode the information and report the physical position of the device on the ground.
Active Antenna
An amplifying antenna that "boosts" the GPS signal before sending it to the receiver.
Active Leg
The part of your journey - between two waypoints - at which you are located.
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 tune in and acquire a new satellites data shortly after it is sent into orbit and activated.
Altimeter
An instrument for determining height position and elevation above sea level by barometric sensing of pressure..
Analog Signal
The principal feature of analogue signals is that they are continuous and reliable.
Atomic Clock
The most precise form of timekeeping ever devised. The Atomic clock operates using the elements caesium or rubidium. A caesium clock has an error time calculated at one second per million years. GPS satellites are equipped with multiple caesium and rubidium clocks.
Azimuth
The horizontal directional line (bearing) from one point on the earth to another, measured clockwise in degrees (0-360) from a north or south reference line. Beacon
A transmitter emitting a signal in all directions (also called a non-directional beacon). In DGPS, the beacon transmitter also broadcasts pseudo-range 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 called an azimuth). In a GPS receiver.
Carrier frequency
The frequency of an unmodulated output of a radio transmitter. The GPS L1 carrier frequency is 1575.42 MHz.
Cartography
The skill of making maps or charts. Many GPS receivers have built in 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 and 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 device screen. It contains the information the GPS receiver uses to fix its position and time, and is accurate to 100 meters or better.
Cold Start
The sequence by which the GPS receiver downloads the almanac data from the satellites when it is first switched on before determining the position of the device.
Control Segment
A worldwide chain of monitoring and control stations that control and manage the GPS satellite constellation.
Coordinates
A set of numbers describing your location on or above the earth. Coordinates are typically based on latitude/longitude lines of reference or a global/regional grid projection.
Coordinated Universal Time (UTC)
Adopted as the world standard for time in 1986 when it Replaced Greenwich Mean Time (GMT). UTC uses atomic clock measurements to calculate and adjust by seconds each year to compensate for changes in the earth s orbit.
Course
The compass direction you take when setting out from one waypoint on a journey to the next (measured in degrees, radians, or mils).
Course Deviation Indicator (CDI)
A system used by your device for displaying the amount and direction of wayward travel through Crosstrack error (XTE).
Course Made Good (CMG)
The bearing from the 'active from' position (your starting point) to your present position so far.
Course Over Ground (COG)
Your direction of movement relative to a ground position.
Course To Steer
The direction (heading) you need to maintain in order to reach a required destination.
Course Up Orientation
Fixes the GPS receiver's map display so the direction of navigation is always "up"
Desired Track (DTK)
The compass direction between a set of "from" and "to" waypoints.
Differential GPS (DGPS)
A supplement to the GPS system that uses land borne radio beacons to transmit position corrections to GPS receivers. DGPS reduces the effect of selective availability and can improve position accuracy by up to x10 .
Dilution Of Precision (DOP)
A measure of the GPS receiver/satellite geometry. A low DOP value indicates better relative geometry and higher corresponding accuracy. The DOP indicators are GDOP (geometric DOP), PDOP (position DOP), HDOP (horizontal DOP), VDOP (vertical DOP), and TDOP (time clock offset).
Distance
The distance between two waypoints or from your current position to a final destination waypoint. This distance can be measured in straight-line (rhumb line) or great-circle (over the earth) terms and can be in miles, kilometres, feet or metres. The GPS defaults to using great circle calculations for distance and desired track.
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.
Ephemeris Data
Current satellite position and timing information transmitted as part of the satellite data message.
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)
Using a calculation of your position, speed and course, this is the amount of time it will take to reach your destination.
Estimated Time Of Arrival (ETA)
The estimated time you will arrive at a destination.
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.
Geographic Information System (GIS)
A computer system or software capable of assembling, storing and displaying geographically referenced information (i.e., data identified according to their location).
Geosynchronous Orbit
The specific orbit of a satellite rotating 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. (Also known as a geostationary orbit).
Global Positioning System (GPS)
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 known as the NAVSTAR system).
GoTo
A journey consisting of one leg of a route, taking your present position as the start, with a named waypoint as the destination.
Greenwich Mean Time (GMT)
Located on the Prime Meridian (zero longitude), it is the mean solar time for Greenwich, England; GMT is used as the basis for calculating standard time throughout most of the world and is based on the rotation of the earth.
Grid
A pattern of regularly spaced horizontal and vertical lines forming square zones on a map used as a reference for establishing points.
Heading
The direction of your course or movement.
Healthy
A term used when an orbiting GPS satellite is suitable for use. (i.e. a healthy state)
Input Output (I/O)
The two-way exchange or transfer of GPS information to or with another GPS device.
Initialisation
The first time a GPS receiver orients itself to its current location and collects almanac data. After initialisation has occurred, the receiver remembers its location and acquires a position more quickly because it knows which satellites to look for.
Invert Route
To display and navigate a route from end to beginning for purposes of returning to the route's starting point. (Commonly known as trackback).
LI Frequency
One of the two 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 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 band within which, the GPS carrier frequencies reside. (1227.6 MHz and 1575.42 MHz). Its total range extends from 390 MHz to 1550 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 (leg) of a route encompassing the distance covered between a starting waypoint and a destination waypoint. To explain with an example:
A route that is comprised of 4 waypoints (A, B, C, and D) would contain 3 legs.
- The distance between waypoints A and B would be leg 1.
- The distance between waypoints B and C would be leg 2.
- The distance between waypoints C and D would be leg 3.
Lithium
A highly reactive metallic element that is used in batteries (Lithium Battery) where weight and the effect of cold weather conditions on a device are of primary importance.
Line Of Sight (LOS) Propagation
The path of an electromagnetic wave from the transmitter to the receiver should be unobstructed. The need for LOS propagation essential at GPS frequencies.
Liquid Crystal Display (LCD)
A display circuit characterized by a liquid crystal element sandwiched between two glass panels. Characters are produced when an electric field is applied to liquid crystal molecules by arranging them to act as light filters.
Longitude
The distance east or west of the prime meridian (measured in degrees). The prime meridian runs from the north to South Pole through Greenwich, England. (See GMT).
LORAN
Loran, (Long Range Navigation), is a grid of radio waves in many areas of the globe that allows accurate position plotting.
Magnetic North
Represents the direction of the north magnetic pole from the observer's position. The direction a functional compass will point to.
Map Display
A graphical or imaged representation of a geographic area and its features.
Mean Sea Level
The average level of altitude of the ocean's surface, as measured by the level halfway between mean high and low tide. Used as a default system to determine altitude or sea depths.
Multipath Error
Fuzzy or double display images on your GPS device are caused when a signal reaches the GPS receiver antenna by more than one path. This is usually because one or more paths have been used (crossed) to retrieve the data.
Multiplexing Receiver
A GPS receiver that switches at a very rapid rate between more than one satellite. Multiplexing receivers usually require more time to acquire a satellite fix and are not as accurate as parallel channel receivers, making them the less reliable of the two systems.
Navigation
The act of determining the course or heading of movement.
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.
North Up Orientation
Fixes the GPS receiver's map display so north is always fixed at the top of the screen.
Parallel Channel Receiver
A continuously tuning tracking receiver using multiple receiver circuits to track more than one satellite simultaneously.
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 (GPS reading).
Position Fix
The coordinates arrived at by the GPS receiver's computations.
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.
Quadrifilar Helix Antenna
A type of GPS antenna in which four spiralling elements form the receiving surface of the antenna. For GPS use, quadrifilar antennas are typically half-wavelength or quarter-wavelength specification and encased in a protective plastic sleeve for durability.
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. (see waypoints)
Search The Sky
Data shown as a message on your device screen when it is gathering satellite almanac data. This data tells the GPS receiver where to look for each GPS satellite.
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 bounced underwater sound waves to detect and locate submerged objects or to measure the depth of a body of water.
Speed Over Ground (SOG)
The actual speed your GPS device is moving over the ground. This may differ from other recordings of speed, such as airspeed or nautical speed depending on head winds or sea conditions.
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.
Straight-Line Navigation
Travelling from one waypoint to another in the most direct line and encountering no obstacles.
Time To First Fix (TTFX)
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. Time to First Fix (TTFF) is the time it takes a GPS receiver to find satellites after the user first turns it on (when the GPS receiver has lost memory or has been moved over 300 miles from its last location).
Track Up Orientation
Fixes the GPS device's map display so the current track heading is at the top of the screen.
Track (TRK)
Your current direction of travel over ground (same as Course Over Ground).
Transducer
A device, much like a microphone, that converts input energy of one form into output energy of another. Anglers and marine explorers utilise this system for underwater searching.
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.
True North
The direction of the North Pole from your current position. 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.
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. User interface - CD screen and its use)
User Segment
A term loosely used to describe you, our GPS / Sat-Nav device and the uses you put it to.
Velocity Made Good (VMG)
Your rate of travel (velocity) to a destination based upon your current speed and course.
Waterproof
IEC 529 is a European system of test specification standards for classifying the degrees of protection provided by the enclosures of electrical equipment. An IPX7 designation means the GPS case can withstand accidental immersion in one meter of water for up to 30 minutes. An IPX8 designation is for continuous underwater use.
Wavelength
The distance between points of the corresponding phase of two consecutive cycles of a wave.
Waypoints
Waypoints are locations or landmarks worth recording and storing in your GPS device and which you may wish to return too at a later date. If you know of a place where refreshment and rest can be taken at certain points along a hard to navigate route, you can enter it into your device (maybe using a detailed map) and it becomes a waypoint; it could also be anything from a distinguished landmark, a bend in a river or any feature that distinguishes itself by being memorable.
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.
WGS-84
World Geodetic System, 1984. The primary map datum used by GPS. Secondary datum's are computed as differences from the WGS 84 standard.
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