Date: Fri, 24 Feb 2006 14:56:54 +0000From: Steve Kennedy <[EMAIL PROTECTED]> Subject: Re: [Asterisk-Users] GPS-enabled cell phone/PDA On Fri, Feb 24, 2006 at 07:17:52AM -0600, Rich Adamson wrote: Its my understanding the cell phone coordinates are sent to the cell phone provider and their equipment reads (and holds) that data. Its not part of any data available to you in any form unless you talk to the cell provider and convience them you have a valid need. Highly unlikely in the US anyway. Even if you could convience them to provide it, they would likely demaand some sort of out-of-band data transmission facility. GSM networks have the Cell ID available to the phone, however that's not much use without the location of the cellsite. There are now location based services, whereby you can query the network and they'll give out an approximate location (most cells are sectored [6 sectors per cell) which gives a direction, the cell also knows what power the phone is transmitting with, and the power it's received so can make a good approximation of where the phone is (within 60 degrees angle). However it's likely a phone will be picked up by several cells, so the network can triangulate and make a better aproximation. Making the information available to end-users is problematic due to privacy issues, unless the user explicitly agrees to give the info away. With GPS units, the info is stored in the phone and can send it out using SMS or other means.------------- It was my impression that only a handful of cellphones have full GPS units in them. Benefon and some Motorola units made for the former Nextel come to mind. The Benefon units do send SMS reports, and in fact, I have written code to control and track these units via SMS using a Nokia 31 GSM terminal. Unfortunately, aside from their unique GPS/SMS capability, the Benefons are not very attractive products, in my opinion. And they are expensive. The Motorola units contain Java machines and a well defined API for accessing the location data. I have not worked with them. There have undoubtedly been changes in the marketplace since I did this work about 2 years ago. As I understand it (but don't have thorough knowledge and could be mistaken), other units generally only receive GPS satellite signals and relay the data to cellular provider networks where the actual location calculation is done. This can be done with assistance of data obtained based on tower proximity, which jumpstarts the iterative process of approximation. I think it is called assisted GPS or some such... |
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