Real Distance Vs Horizontal Component

Q. Maybe you can answer a walking GPS question that has always bugged me. If you walk 1 km up a 45 degree slope, will the GPS register that you have walked 1 km, or will it only register the horizontal component of the distance, i.e. 1/√2 km, which is 0.71 km. Presumably it would register your vertical ascent correctly at 0.71 km, but I want to know if these devices are smart enough to take into account at every stage in a walk, up or down, how steep the slope is. Of course the ultimate example would be if you were to climb 1 km up a vertical rock face (unlikely I know), would it register that you had travelled 1 km or 0 km? Any ideas?

Simon Capelin, Girton

A. GPS signals are received as Latitude, Longitude and Altitude. Most GPS units just measure distance from changes in Latitude and Longitude. If the slope is shallow then the difference is probably to small to matter : if the slope is very steep the route will almost certainly be a shallow zig-zag. But the discussion is more theoretical than practical - roughly, to make a 10% difference the slope needs to be about 1 in 2.1 - which is too steep to walk easily.

John Thorn, Cardiff

A. It depends on the gps. By default they will give you the horizontal distance. I have a Garmin Epix and there is an opiton to turn on 3d speed and distance, which gives you the distance you are asking for. This probably isn't an option offered by all gps units however.

Lloyd Atkins, Norwich

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