Measuring velocity via iPhone SDK

Question

I need to implement a native iPhone app to measure the velocity of the phone (basically a speedometer). I know that you can do so via the CoreLocation API fairly easily, bu

Answer 1

The error in the acceleration will accumulate over time. Your best bet is to get an accurate velocity from the GPS, maybe once a minute or less:

distanceTravelled = sqrt( (position2.x-position1.x)^2 + (position2.y-position1.y)^2 )
velocity = distanceTravelled/timeBetweenGPSReadings

(where ^2 means squared)

Then take frequent measurements of the accelerometer:

newVelocity = oldVelocity + accelerometer*timeBetweenAccelerometerReadings