GPS or Global Positioning System was originally developed by the US Military and utilises a series of satellites that send very low power radio signals to Earth, enabling anyone armed with a GPS to pinpoint their location with very high accuracy, anywhere on the Earth's surface. To gain a position a GPS needs to be able to locate a minimum of two satellites, however, three satellites are required to 'triangulate' a position. Most GPS on the market have the ability to receive a signal from up to 12 satellites at any one time. Ultimately the more satellites a GPS can receive information from at any one time, the greater the accuracy of the position. As a general rule most GPS are accurate within 4-5 metres of a position.

GPS is an invaluable tool for anyone who indulges in boating, hiking, fishing and 4WDing. Coupled with traditional navigational devices such as a map and compass the average person should have sound peace of mind when touring in remote or unfamiliar country. 

Selecting a GPS
Non Mapping
Non Mapping GPS do not have the ability to load mapping software but can plot an overhead view of your location, relative to waypoints, routes, marks or track logs.

Base Mapping
If a unit is described as providing the base mapping ability then it will typically display highways, rivers, lakes and coastlines. These units are useful for obtaining ones 'bearings' against obvious landmarks.

Mapping
The most advanced GPS technology available on the market today are mapping capable GPS. Data is loaded onto the GPS unit from either a CD-ROM or secure digital media card that is usually purchased separately from the unit. Customers can choose a chart or map to suit their specific area, however, the trend from chart and mapping companies is moving to providing customers with all of Australia on one chart. The information uploaded is extremely detailed and will display an array of information. For marine charts information contained includes navigational aids, tidal information, depth contours, marinas and various points of interest. Land-based chart information may include local streets, tracks, topographical contours and points of interest.
In-car street navigation units also fall into this category. These units are generally pre-loaded with detailed street maps for all of Australia. They allow the user to enter the address of their required destination and provide turn by turn navigation using both visual and audio prompts.


Getting Started

Waypoints
No matter which unit you select, be it mapping or non-mapping the underlying principle is the same; you need to know where you are in order to get to where you want to go. This is where 'waypoints' come in. Typically, waypoints are a point of interest , a boat ramp, a road junction, secret fishing spot etc. Some people may refer to waypoints as 'marks'.The user inputs waypoints by entering the latitude and longitude data of their current position or destination. Most GPS will then use a 'GOTO' function to get from waypoint A to waypoint B.

Routes
Routes are essentially a series of waypoints that are plotted and navigated in a predetermined order. A route can be created by using waypoints which are already stored in the GPS or from obtaining GPS coordinates from a chart, using these points to create a route.

Track logs
Your GPS will automatically record your movements each time it is activated; this is called a track log. Think of track log as a 'breadcrumb trail' that can trace thousands of points of where you have been. Every twist and turn is recorded so that if you want to retrace your steps or path exactly, you can. This is a great safety feature, for example, if you were out on the water and night time fell and visibility was poor, you could retrace your path and return to your set off point safely.

Things to consider when buying a GPS

Battery Life
In the case of a portable or handheld GPS, if the unit is to be used away from a power source the amount of battery life required should be considered. Some units run on in-built rechargeable batteries and others may require standard household batteries. It is a good idea to consider the extra weight of carrying extra batteries. Full colour GPS will decrease battery life at a greater rate than grey scale models.

Auxiliary Antenna
Most GPS on the market have internal antennas with the option of an external one.  GPS signals will not travel through steel or other hard structures. As a rule they need to be able to 'see' the satellites. The signal can also be affected by dense scrub, with some GPS units losing their signal. By fitting an auxiliary antenna the ability to receive satellite signals will be significantly improved in such situations.

Software
If a mapping GPS is selected, it is important to consider the additional cost which may be required to purchase the correct software to cover the areas you wish to travel or navigate.

Most reputable GPS brands will support their product with PC software which will allow the user to perform a range of tasks. Features of such software vary but generally allow the user to upload stored information from their GPS to the PC for archiving purposes and download information back into the GPS such as waypoints and routes. In some cases this software is provided as a free service, however, generally it is sold as an optional extra. A PC to GPS cable is also required to allow the units to 'talk' to each other.