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Message: <blockquote data-quote="mikelsc" data-source="post: 2258291" data-attributes="member: 52377">b00n,The commercial channel of GPS is free for everyone to use. There is no payment levied in anyway for receiving GPS transmission. This is very much like radio. You can receive radios all over the world without having to pay anyone. Just buy a receiver. You can buy a GPS receiver with bluetooth capabilities at Low Yat or even Imbi Plaza. Taiwan makes lots of it. Some of them are very small indeed. If you have a handhone or PDA or PC with bluetooth, you can hook it up and start receiving messages from the GPS device. Next you need something like MAPKING and wham .. you have a navigation system. Some models of Nokia like the N95 comes builtin with a GPS receiver and a Navigation Software which can use all over the world. Again .. no charges for GPS .. you need to pay for the phone though.Another thing, you dont send anything to a GPS receiver. The GPS receiver is the one that sends things to you. The contents of the message it such that the receiver can determine its *own* location if it can receive messages from at least 4 statellites. So the receiver knows where it is. So for a tracking system, it needs some way of sending this location information back to someone who is interested in it. That is where GSM comes in.About activation and sending of messages ... this depends on how a device is programmed to work. In most cases, GPS /GSM devices requires to be interrogated in order to know where it is ... for example when an alarm is received. This means, as you say, send a message to it and it returns the information to you. This is fine but there is a fundamental problem with GPS. What if it is in a basement when it is interrogated? Well, it will just tell you that it does not know where it is.Devices can also be programmed to transmist periodically .. automatically .. However, with SMS, this is going to be very very expensive .. as you said .. a bomb. However, if the messages are very short, then GPRS would be a whole lot cheaper. Periodic transmission would also mean that you will know the last location of the vehicle before transmission stops or when GPS positioning is lost ... as in a basement. Besides digi is offering RM33 for a sub data line unlimited usage.Hope this will finally answer your question ... and did not sound like an ad for digi.As for Satellite imaging, you will need to get incontact with MACRES (Malaysian Center for Remote Sensing). They have a list of about 10 satellites that can take picures for you. Use Google .. you will find them. (not a google ad either :regular_smile: )cheers ...</blockquote>