Auckland Baptist Tramping Club

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Twelve people took advantage of the opportunity to learn about the GPS, the latest technology in helping find your way in the bush and in the back country. We enjoyed the excellent instruction from our club president Peter, greatly assisted by GPS whizz-kid Simon.  

We met at the Bracken at 9am then moved over to the Ngaire Avenue Chapel nearby for our classroom session. Peter told us that, to be able to use a GPS, one would need to be familiar with the grid references on a topo map. He explained what eastings and northings were, then brought out a few maps so if we could have a practice at finding grid references.  

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After our morning tea break, with tea coffee and biscuits, Simon began to talk about the GPS. The GPS, or global positioning system, consists of a network of satellites about 12000 miles above the earth that orbit the Earth twice each day. The satellites run on solar power with backup batteries. These satellites in with radio signals that are picked up by GPS receivers; these receivers use these signals to work out the exact location of the user. The accuracy of the location varies a lot, depending on the number of satellites that can be picked up, and obstacles such as trees all buildings. The accuracy can also be reduced when special errors are introduced during times of military operations to avoid detection by the enemy.  
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GPS was originally set up for military purposes, but in the 1980s the US government made the system available for civilian use. It was not until the end of the 1990s that GPS equipment small enough to fit into a tramp his pocket was developed.  

Simon told us that the GPS can be as accurate down to 4 metres, but usually when the selective availability function is switched on accuracy is about 50 metres. A GPS unit can work out a position on the map with 3 satellites, but to get the three-dimensional positioned including altitude and unit would need to lock into four or more satellites. The reading of a GPS is not affected by the weather but can be affected by a sun spots, solar storms and other things that can affect radio signals. The GPS supplements but does not replace map and compass - these must also be taken.  

We then learned about waypoints, the GPS description of grid references. Waypoints entered from a map reading will never be as accurate as those entered in the field, as sometimes there can be mistakes on the map, but can still be very useful in navigation.  

We moved from the classroom to the field, driving to One Tree Hill and Cornwall Park. We split up into two groups, each group having a GPS receiver. Several waypoints had already been programmed into the receivers, and our exercise was to use the units to find these points. Each person in the group had a turn and using the GPS to find a point - not as easy as it sounds!
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Our course led us to the top of One Tree Hill, where we had a short break for lunch.  
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And, of course, it was the lambing season.  
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The main conclusion of the exercise was not only how to use the GPS in the field up to use it in conjunction with a map, and to realise the accuracy, or lack of accuracy, of these units.  

We finished about 2pm and relaxed over afternoon tea at McDonalds in Green Lane before going home, having learned a lot about this new aid to navigation in the bush or back country.  

COST: $5