|
|
General information on GPS
GPS receiversGPS receivers calculate their position from the time difference between signals of several satellites. Important is that your receiver has a clear view to the sky. Between trees or high buildings your GPS will not receive signals from some of the satellites from time to time. GPS cannot calculate your position at those moments.Positions of all satellites are preprogrammed in your receiver. When signals of at least four satellites are availlable receiver calculates your actual postion from time differences between signals received. This will give you a three dimensional position, location and hight. The hight indication will not be very accurate though.
24 satellites are in operation constantly to have GPS system available all over the world. This system is maintained by U.S. Air Force and is payed for by the American Ministery of Defense. Accuracy is very high, actually between one and twenty meters is possible
for militairy use. Civil use is free of charge, since signals are send
anyway. In the last years S/A (Selective Availability) is used to make
worse the accuracy intentionally for civil use. With S/A on the accuracy
used to be between 30 en 100 meter. On May 2, 2000 S/A was switched off
(see article IDG from CNN-Today).
From that moment on we all could have the advantage of a very high accuracy,
with deviations less than 10 meters.Whenever military circumstances require
S/A will be switched on again, when needed for a part of the globe or
all over. DGPSIn navigation, road-building and hydraulic engineering and aviation accuracy can be lifted by using DGPS. This technique uses an extra signal from a fixed source at ground level.This gives you a known calibration point, allowing accuracies better than 1 meter. More specific information on GPS and Differential GPS you can find on the Internet, for instance at: http://www.joe.mehaffey.comhttp://www.trimble.com
Interface with other applicationsFrequently GPS receivers are used providing mobile computers, APRS transmitters or automatic steering equipment on yachts with navigational data required. Or just to communicate with your routing program at home. For this connection you will need a cable or interface. Your GPS will communicate using one of the provided communication protocols. Which one you should use is indicated in program you use. NMEA is very common for routing programs and GARMIN for sending simple data. With some workmanship you could make your own cable using a Pfranc connector. Icarus Solutions is importing these plugs into the Netherlands. For other countries please check your local dealer at http://www.pfranc.com. Furthermore we can supply high quality ready-made cables. How to learn the navigation priciples?Some basic knowledge on how to use a compass is a very important first step to get to know GPS. In critical situations you should never have a hundred percent confidence in what your GPS is telling you. Sure GPS is accurate and it allways has wored great. But batteries could fail unexpectedly. Or your trip takes longer that thought. Your GPS is dropped overboard! You surely will find a good book in your own language. Updated: 09.04.2005 |
