Applications can call on any of several types of positioning methods.
Using the mobile phone network: The current cell ID can be used to identify the Base Transceiver Station (BTS) that the device is communicating with and the location of that BTS. Clearly, the accuracy of this method depends on the size of the cell, and can be quite inaccurate. A GSM cell may be anywhere from 2 to 20 kilometers in diameter. Other techniques used along with cell ID can achieve accuracy within 150 meters.
Using satellites: The Global Positioning System (GPS), controlled by the US Department of Defense, uses a constellation of 24 satellites orbiting the earth. GPS determines the device's position by calculating differences in the times signals from different satellites take to reach the receiver. GPS signals are encoded, so the mobile device must be equipped with a GPS receiver. GPS is potentially the most accurate method (between 4 and 40 meters if the GPS receiver has a clear view of the sky), but it has some drawbacks: The extra hardware can be costly, consumes battery while in use, and requires some warm-up after a cold start to get an initial fix on visible satellites. It also suffers from "canyon effects" in cities, where satellite visibility is intermittent.
Originally posted by Greg Schwartz:
Was your work with MS Map Point at a J2ME level? Did this require GPS phones?
Originally posted by a sanjuan:
all j2me location service companies use gps phones right now, i believe...there are several of them as far as i know, espcially crowded around Nextel's IDEN.
Originally posted by Michael Yuan:
I can start a "j2me location service company" and use MapPoint (carrier based location) as my backend today. Seriously, Russell Beattie's waveblog has J2ME/Symbian bas