Getting the Velocity of a Moving Object via GPS

It compares the signal from at least two, preferably three or more satellites overhead and computes your location/speed from that information. Under ideal conditions it can locate you within about 6 feet.

Global Positioning System - Wikipedia, the free encyclopedia

If you know when a signal from a satelite is sent and where it was sent from and you know how fast the signal takes to get from the satelite to you and you add or subtract the information from say a satelite behind you and one in front of you the difference is your speed.

now if you take the time and position of say four signals approaching you from say the four points of the compass you could work out where on the planet you are.

so if you was to stand in a field say 100 square metres cubed if the distance in four directions from you is say 50 metres in forward bacjwards left and right, by my recokning you would be in the middle.

so the more the points of information the more accurate the information.

Got it ?

http://www.pocketgpsworld.com/howgpsworks.php

Take a position fix, take another position fix, time how long between the two.

Do this over and over.

GPS chips actually update about once a second, so what you see is being *guestimeted* in between, and smoothed.

Speed , as explained above, is nothing but your time over a distance.

So for instance; 60mph *actually* means 60 miles traveled in 60 minutes.

Or one mile a minute.

i see... thanks for all the information.. but just give me a bit more time to digest all the information...

Lynnbob,

Welcome to CR4. I have given you your first Good Answer (GA)!

Most people think that GPS simply calculates 2 positions, and divides by time. However, you are correct that the doppler effect is used, increasing accuracy.

You have some good answers already, but I would like to correct your question!!!

"A GPS will usually knows approximately what speed is your car moving at..."

A GPS that shows speed is AMAZINGLY accurate provided you are driving on a fairly straight road. On one with a lot of twists and turns the accuracy will drop, but still be probably no worse than most speedos!!! Trust it implicitly.....

I use my Tom Tom as a speedo and have never been charged with driving too fast.....