GPS on iPhone 3G not updating during a high speed elevation change

I have written an iPhone app that is supposed to detect rate of eleva开发者_运维百科tion change during a high speed fall. I am using kCLLocationAccuracyBest. The accuracy is more than adequate during horizontal location changes, but is not giving accurate results during a free fall. I can however walk the same elevation change (50 feet) and get accurate elevation numbers as I walk. Is there a problem with measuring a free fall with the iPhone GPS? I am testing with a 3G. I am not sure if I would get any better results with 3GS or 4.

It looks like the iPhone GPS calculations can't handle high speed elevation changes. Is this correct? Is there any work around?

Thanks in advance.

Take a look at the Core Motion Framework Reference. It sounds like to need accelerometer/gyroscope data, not just GPS.

It may be that the iPhone is programmed to more or less ignore changes in elevation when sending updates. Have you tried setting an NSTimer and polling the CLLocationManager's location property? Or it may be that it simply doesn't calculate its position frequently enough fotr your purpose.