Does GPS take topography into account when calculating speed?

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Terence Harrison

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Terence Harrison  asked the Naked Scientists:
Hi Naked Scientists,
Re: GPS speeds.  Do GPS take into account the topography of the Earth, or are the maps used only 2 dimensional, if so, if I were travelling up or down a steep hill would the GPS give only my forward speed or also add the relevant change in hight which I think would add to my ground speed?
Sorry about the spelling I was never a good student, but I love listening to you podcast keep up the fantastic work. 

Terry ( Wombat ) Harrison, Queensland Australia.

What do you think?
« Last Edit: 14/12/2010 09:30:03 by _system »


Offline CliffordK

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Does GPS take topography into account when calculating speed?
« Reply #1 on: 14/12/2010 09:58:04 »
Your GPS should be able to track 3-Dimensional movement, although the vertical accuracy is generally lower than horizontal accuracy. 

However, the relative precision of the vertical measurements should be better...  I.E. if you are off by 20 feet on the vertical, it doesn't make any difference as long as you know when you've descended or ascended by an additional 10 feet.

Thus, your system should be able to use both horizontal and vertical measurements as part of its calculations.

There are also quite accurate surveys available. 

A smart system should be able to overlay your movements onto a 3-D map to improve the performance.  However, it is unclear the exact algorithm being used.