How to get velocity from variable accelerometer(in simple linar motion)?

I want compute the current iphone motion velocity a开发者_运维问答nytime based on accelerometer, the accelerometer is variable. Anyone can give any idea?

It's basically impossible. The only way is to integrate the acceleration, but that magnifies the inaccuracy of the iPhone's not very accurate accelerometer, and because you don't have an independent orientation sensor (the iPhone uses gravity to figure that out!), you can't distinguish lateral acceleration from tilting the phone.

How people do this in the real world is to measure velocity using something else like GPS, and use the accelerometer to interpolate.