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Một tính năng phổ biến trên các thiết bị di động hiện hành có khả năng GPS, do đó, các thiết bị có thể cho bạn biết nơi bạn đang ở bất kỳ điểm nào trong thời gian. Trong khi sử dụng phổ biến nhất của các dịch vụ GPS là dành cho lập bản đồ và nhận được hướng dẫn, có những thứ khác bạn có thể làm gì nếu bạn biết vị trí của bạn. | . 32 Chapter Accessing Location-Based Services A popular feature on current mobile devices is GPS capability so the device can tell you where you are at any point in time. While the most common uses of GPS services are for mapping and getting directions there are other things you can do if you know your location. For example you might set up a dynamic chat application based on physical location so you re chatting with those people who are nearest to you. Or you could automatically geo-tag posts to Twitter or similar services. GPS is not the only way a mobile device can identify your location. Alternatives include the following The European equivalent to GPS called Galileo which is still under development at the time of this writing Cell tower triangulation where your position is determined based on signal strength to nearby cell towers Proximity to public Wi-Fi hotspots that have known geographic locations Android devices may have one or more of these services available to them. You as a developer can ask the device for your location plus details on which providers are available. There are even ways for you to simulate your location in the emulator for use in testing your location-enabled applications. Location Providers They Know Where You re Hiding Android devices can have access to several different means of determining your location. Some will have better accuracy than others. Some may be free while others may have a cost associated with them. Some may be able to tell you more than just your current position such as your elevation over sea level or your current speed. 295 CHAPTER 32 Accessing Location-Based Services Android has abstracted all this out into a set of LocationProvider objects. Your Android environment will have zero or more LocationProvider instances one for each distinct locating service that is available on the device. Providers know not only your location but also are aware of their own characteristics in terms of accuracy cost and so on. You .
