How to calculate speed of our car using iphone

For my application I want to calculate my car/bike speed using iphone. How can i do that? Ideally, it should开发者_如何学JAVA run continuously in the background.

CLLocation includes a speed property that will give you the current speed of the device. (Note the comment about the accuracy at that link.)

To get the user's current location, follow the steps in the Location Awareness Programming Guide, under "Getting the User's Current Location".

Finally, to enable location updates in the background, see Receiving Location Events in the Background in the iOS Application Programming Guide.

the only way i can think of is thru GPS. the accelerometer is out. but im not sure if enough information is provided thru "GPS API".