Navigation Techniques.

Navigation Techniques. A simple guide to using GPS, a Compass and map. Reproduced by kind permission of Land Rover World Magazine.

We’re on the road to nowhere.

Navigation has been the key to our small island’s success over the course of history. Sir Francis Drake became the first man to sail round the World way back in the sixteenth century, Sir Walter Raleigh discovered America in 1585 and Capt. James Cook made the first European landing on Australia’s east coast in 1766. They all achieved their great status by being a dab hand with a sextant, compass and chart.
We rely on much the same technology today, but with the very useful addition of G.P.S. In this guide we shall look at the most useful and available methods of navigation relevant to driving off road.

Maps

For King and Country.


We are most fortunate in the UK, in having highly detailed maps published by the Ordnance Survey. They date back to 1746, when King George 2nd commissioned a detailed survey of Scotland to aid victory in quashing the Scottish Rebellion. From then until now they have remained similar in layout and cover the whole of the British Isles. For our purposes there is a choice of scale, The Landranger series at 2 cm to 1 km, or the bigger Explorer  at 4cm to 1 km. Learning to read them is both rewarding and useful.

For the purposes of being able to pinpoint a unique OS map reference, the UK is split up into a grid of 500 km squares. Each of these is sub divided into 100 km x 100 km squares which are allocated a two letter reference. These squares are then sub divided by 10 km horizontal lines and vertical lines, known as meridian, and then again to reduce the area to 1 km squares.

In the illustration (Fig 1) I have chosen an area on the OS Explorer  map OL30 of the North Yorkshire Dales. Imagine the scenario that you are stuck up to your axles in mud somewhere on Carperby Moor where the unclassified track may have some deep ruts. You need to phone your mate with the winch and ask for assistance. This particular area is right on the borders of two 100 km squares. You are stuck in square ‘SD’, to the west (left), not square ‘SE’ to the east (right). As you are in the most easterly km of that square the ‘easting’, or distance to the east (right) of the final km. meridian of that square, would begin SD99 and the ‘northing’, the distance north (above), would be 91. To be more accurate you could then use a ruler and sub divide the square into 10x10 squares and give a full six figure map reference of SD 991 916. To aid this there is a small scale at the top of the map and I have drawn in two green lines to represent your position. It would be helpful to also tell your mate you are using OS Explorer map OL30, though the grid reference would be exactly the same on any OS map.

 

 


One other thing to be learn from this map is that you are at 410 metres above sea level. This is represented by the thin brown line. The thicker ones adjacent to it are 400 m and 420 m so it’s been a steep climb from the end of Peatmoor Lane!

Going Global.

If you venture from these hallowed shores you will need to familiarise yourself with an international system, as used by Drake, Raleigh and Cook. This uses Latitude and Longitude. Latitude lines are the ones that run from east to west, are parallel and 111 kms (69 miles) apart, starting at the equator, which is 0º and ending at the North and South Poles which are N90º and S90º respectively. Longitude lines run from the North Pole to the South and at the Equator are 111 kms (69 miles) apart, converging as they go north and south. For this reason they are not parallel, but curve with the shape of the planet. 0º is at the Royal Greenwich Observatory in London, with 180º stretching west and 180º stretching east. Where they meet, in the Pacific Ocean, is the international date line.

Like our OS maps, the planet is sub divided into a grid, but made up of degrees, minutes and seconds and specifying North (N) and South (S) of the Equator, East (E) and West (W) of Greenwich. As with a clock, there are sixty minutes and sixty seconds dividing the grid. In this example (Fig 2) I have used Michelin map 953, Africa North and West. The scale is small at 1 cm to 40 km. The selected location is Ksar Ghilane in Tunisia, visited by Land Rover World in the March 2007 issue.

The latitude to the south (below) is ‘N32º’.    N36º is off the picture to the north and we have to calculate N33º and N34º as these are not shown on this scale.
The longitude to the west (left) is ‘E8º’ and to the east (right) is ‘E12º’.      E9º, E10º and E11º we, again, have to draw in ourselves. I have done this with red lines.

Remembering that these squares can be sub divided into 60 minutes, then a further 60 seconds, it is possible to give an accurate map reference in this way too and, despite being several hundred years old, this is still the Internationally used method of navigation.

For the record Latitude and Longitude are quoted on OS maps as well, along the extreme edges.

The Compass.

You can take all the technology you like, but never forget your compass. This simple magnetic devise will always show you which way is north and in the days before G.P.S. was the most widely used accessory to navigation. A simple revolving metal needle is attracted north by the Earth’s magnetism and from this you can calculate your direction of travel, either in terms of cardinal points, North, South, East or West, or parts thereof. Or in degrees, which are shown around the edge of the compass housing from 0º to 360º.

To use your compass to calculate the direction you need to travel in, simply line the edge of the compass up with the A to B route you wish to take. In this case a B.O.A.T. in Northamptonshire. It is important to know exactly where you are to start with. In this example you will have driven past Home Farm on the left and will have come to a fork in the road. It will be blatantly obvious which way to go, but for the purpose of this exercise, rotate the  compass housing so that the North/South lines are parallel with the  North/South meridians on the OS map (Fig 3).

 

Then revolve yourself, the map and the compass until the red part of the needle is lined up with the North marking on the housing. The direction of travel arrow will now point the way you have to go. In this case (Fig 4) Northeast on a bearing of 58º. Before setting off you should look in that direction and spot a tree, or similar landmark. Aim for that, then repeat the process when you get there.

 



In this exercise declination would not be an issue, but for more serious orienteering you would need to consider the variation between True North and Magnetic North. This is shown on OS maps and here would have needed correcting west by 03º13”.

G.P.S.

God bless America


The Global Positioning System was invented by the Americans for military applications, but fortunately for us, they made it available for civilian use, free of charge, back in the 1980’s. This has led to the huge popularity of G.P.S. units with ‘Sat Nav’ being the favourite car accessory. The system works by sending and receiving constantly updated messages from satellites in geo stationary orbit. Software within the unit then calculates an exact position to within about 10 metres. The more advanced in car ‘Sat Nav’ also has mapping software within it, but the unit featured here has a simple Lat/Long and altitude reading.

G.P.S. has undoubtedly made the biggest single difference to overland expeditions since the compass. The ability to record exactly where you are on any part of the Globe 24 hours a day gives map reading and trip planning a far greater, and easier, accuracy than ever before. The only limitation is that you do need a pretty good view of the sky. Signal strength can be zero in woodland, or indoors.

Take me home

When you first buy a G.P.S. set aside at least half a day to get to know it. Basic operation is soon learned, but more advanced features take practise, like any piece of high tech gear. Start by recording and renaming your ‘home’ position, or where you have parked you Land Rover. If you then go for a long walk your GPS will remember it’s own waypoints so you can ‘trackback’ and it will take you back the way you came. The next stage is to program in new waypoints, either from calculations made from a map, or from a guide book. In Chris Scott’s Sahara Overland all the relevant waypoints for various desert routes are printed in the back and from this list, waypoints can be manually added to any GPS unit and made into a ‘route’.

 

 


Little things to watch out for are waypoints that are quoted in units other than degrees, minutes and seconds. (hdddºmm’ss.s”) They could be quoted in degrees, minutes and decimal seconds, (hdddºmm.mmm”). If you measure depth in fathoms and still work in fahrenheit, then you will probably favour  hdddºmm’ss.s”, but if you have woken up to the metric revolution you may prefer hdddºmm.mmm”. There is also an option to use the British OS grid references, but I have found this mode to be inaccurate in use. Whichever you choose, if you are travelling in a group it is best to standardise all the G.P.S. units to the same system and preferably the one used in your guide book. This is done in the ‘set up’ menu.

It’s good fun working out how to get the most out of a G.P.S. unit.  I bought the Garmin GPS 12 featured here the day before going on holiday to Corfu. I spent many a happy hour plotting routes round the swimming pool and to and from the bar! Good luck.


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