Functional Features Of A GPS Unit

GPS Unit

Find Accurate Locations With GPS Units


Before you purchase a one for hiking you will definitely need to think about the functional features you want:

GPS Unit Accuracy And Portability – The theoretical accuracy of all GPS units is to approximately 15m. However, more recent devices can be a great deal more accurate. If you buy a GPS unit that is WAAS-enabled (Wide Area Augmentation System), which is a US-based satellite network, accuracy can be up to five times greater. There is also a European version called EGNOS (European Geostationary Navigation Overlay Service) in operation.Compass to navigate

Accuracy – If you need to pinpoint your location to within a few feet then accuracy is an important selection criteria for you and you will need a WAAS-enabled GPS unit. However, there is no point acquiring a WAAS-enabled device if the region in which you intend to use the GPS unit does not have the WAAS service available.

Portability – If portability is an important selection criterion for you then you may need to compromise on accuracy. This compromise may come in the form of poorer GPS unit signal acquisition, software that is not so useful or maps with less detail.

Correction Services – Services such as OmniSTAR provide extra correction information for GPS unit receivers and this enables then to increase their accuracy. Accuracy can also be improved by using a Differential GPS (DGPS) service, usually to within about 3 to 5 meters. However, to get a corrected signal, your device needs to have both a differential beacon receiver together with a beacon antenna as well as the GPS unit. The market leader in this field is OmniSTAR.

Channels – When tracking satellites a GPS unit utilises a numbers of channels. These days the most common are 12 or 16 channel parallel receivers which are better than 6 or 8 channels because they find satellites more easily, especially in woods or in areas that are built-up. Choose a 12 channel GPS unit so you get good reception when in mountainous terrain or covered by trees.

GPS Unit

Choosing Paths Using GPS Units

Co-ordinate Systems – Maps have a grid so you can identify a location using a grid reference. The most common co-ordinate systems in the world are Lat-Lon and UTM:

Lat-Lon – This is an angular co-ordinate systems with latitude and longitude and has been designed to suit 3D objects like our planet. In this system lines do not cross each other at a 90 degree angle, except along the Equator, and therefore is not a grid system.

UTM – Universal Transverse Mercator is a rectangular co-ordinate system and has been designed for 2D objects like a map. In this system lines cross each other at a 90 degree angle, and it is therefore a grid system.

Neither co-ordinate system is more or less accurate than the other. They are both just different methods for locating a point. However, you must set the co-ordinate system of your GPS unit to one that matches the co-ordinate system on the map you are using.


GPS Map Datum – The beginner GPS unit user often fails to consider the notion of a map datum. The earth has an elliptical shape, not a perfectly round shape, and map makers have attempted to correct for this fact with a map datum. Various map datums have been developed and used as points of reference on various maps around the globe. You need to make sure the GPS unit you are using is set to the same datum that your map is referenced to, usually displayed on the bottom left corner of the map.

If you forget to set your GPS unit datum to the same one as your map then this could give you errors of 200 meters, about 600 feet, or possibly more regarding the position shown on your display screen. This difference might be no problem in a large open area where it is possible to see your destination from some distance. However, imagine the dire consequences it could have if you are in a mountainous area. The difference in these two points has the potential to result in a vertical separation of thousands of feet. This may be an even bigger issue if you are hiking in weather conditions that result in poor visibility.You should reference your GPS unit manual to find out how to set the correct datum to match the datum on your map. Also make sure the GPS unit you select has all the map datums you need to use.


Power Supply

An external power supply facility is only useful if you need to use your GPS unit within a motor vehicle or indoors. When hiking in the hills you need to rely on batteries for a power supply. If your chosen device takes replaceable batteries, either throw away or rechargeable, then it is best to make sure they are of the long life type. If you consider a GPS unit that uses its own design of rechargeable battery that is fixed in place then make sure it also has a long life. You don’t want to run out of power on the hills, especially in poor weather conditions.


A GPS Unit With Bright Colour Screen

Display Screen – A display screen needs to be bright with a high definition so it is easy to read, especially when there is bright sunlight. As a general rule, a colour screen makes reading the detail of a map much easier and therefore a colour handheld GPS unit is supeGPS Navigationrior to black and white. As a general rule, the more expensive the GPS unit, the larger and clearer the screen will be. Although you can save money if you choose a simple display screen, if you are unable to read the information then the GPS unit is useless to you. Note that if the GPS unit has a backlight, the life of the battery will be influenced by it so try it with the backlight both on and off.


Digital Mapping Or Not – Digital mapping can display contours details on the display screen of your GPS unit. You can obtain a GPS unit that provides either mapping or no mapping. If you choose mapping you can get either complete OS (Ordnance Survey) mapping, or built-in topographical databases and base maps. However, consider what standard maps are included and how much additional maps cost, if they are available:

Non-Mapping – You can obtain a non-mapping unitwhich provides accurate grid references which you can immediately transfer to your paper map.

Built-In Topographical Mapping – This does not usually provide sufficient detail to navigate accurately in hills and mountains. Basic mapping does not usually display contours details, just your location between roads. More detailed topographical maps can be purchased for some devices, but it’s fairly costly and still does not provide as much detail as OS mapping.

OS Mapping – Before you purchase a GPS unit with OS mapping consider whether or not you need this feature as it is more costly. Even though OS mapping is advantageous when undertaking complicated low level hiking, this advantage is not as important on simple trails or big mountain trails where landscape features are prominent. As well as expensive, OS mapping can be difficult to see on small screens. It also uses up more battery power and thus reduces battery life.




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