GPS + barometer

[bulls23]

Since the iPhone 6 now has a barometer (some Android devices do too btw) I was wondering what I might be needing that for.
Barometers are pretty exact for altitude measuring and GPS isn't (centimeters vs. meters). While altitude may not be crucial on a racetrack I thought it still might be one more sensor delivering an axis of movement and therefore maybe adding to the overall positioning accuracy. I googled it and apparently some Android devices in fact use the additional barometer together with aGPS to further improve the GPS lock. Is this something that's already implemented in the iOS location services and therefore also helping Laptimer accuracy or something that needs to be done by each App developer and would it really make a difference? I guess this is once again something with fancy mathematics and interpolation I know nothing about

[Harry]

I believe iOS has included barometric pressure into their sensor fusion algorithm, but (hopefully) not to tweak GPS data - which is filtered already. I have that item on my list. But I need to add that in the sensor support area, I have tons of possible improvements queued

- Harry

[gplracerx]

Sensor fusion, properly done, should be more accurate and precise than GPS data alone. In sensor fusion, position, velocity and orientation are calculated by integration of the time series of three axis accelerometer and the three axis rotation rate data. If that data were noise free, that's all you would need for inertial navigation. But it isn't and integration of noise leads to drift in the integrated data. GPS, magnetometer and barometer readings are used as absolute references to correct that drift. Unfortunately, the accelerometer and rotation rate sensors in a smart mobile device are very noisy. I've only seen sensor fusion implemented in high end data loggers like the Racelogic VB3i with the IMU04 inertial motion unit attached ( application note here ).

Sensor fusion doesn't take all that much processing power to implement. DIY drones, for example, use an Arduino board with a GPS and a 6, 9 or 10 DOF (9 DOF adds a three axis magnetometer to the three axis accelerometer and rotation rate sensors and 10 DOF adds a barometer) breakout board for real time flight control. They can even correct for cross winds and fly pre-programmed courses. But I've never seen a data logger for vehicles using this technology.