On Wednesday 25 Jun 2008 18:28, Pradeepto Bhattacharya wrote:
Hmm, not sure about different GPS models, the one I haveused I noticed that it could give me 2 different ( parallel ) tracks for walking on extreme sides of a 2 way road and that too in New Panvel where the roads are far less wide compared to those in New Delhi ;).
The two line are relative to itself. I absolute terms you still dont know if the lines are accurate. If you take another model of gps, there will (proly) be a slight difference. If you take the reading under cloudy skies there may be difference.
What is "DGPS with correction data for your locality." ?
Differential GPS. A method of correcting gps errors. Other newer methods are WAAS (Wide Area Augmentation System) and SBAS (Satellite Based Augmentation Systems).
http://www.kowoma.de/en/gps/waas_egnos.htm
GPS systems have errors due to atmospheric / ionospheric delays, reflected signals, timing inaccuracies and sattelite drift. Theses errors (except atmospheric) are nearly the same for an area of a few 100 sqKm. So if you can fix a location triangulated by standard surveying techniques and then take the difference with the one shown by the gps, you have an error correction factor available. Broadcast this factor by radio or over the net or by satellite. Recieve the error factor, feed it to the gps and correct your gps reading.
Very useful when surveying and mapping - given the astronomical prices of real estate.