reckonMe

reckonMe features live inertial navigation and collaborative localisation on an iPhone.

Here's how you use it:

• Un-mute your iPhone so you can hear what's going on.
• Put the red pin onto your starting position on the map. It is automatically moved to the current GPS position until you drag it.
• Tap "Start Dead-Reckoning".
• Put the unlocked iPhone into your pocket.
• Walk around. reckonMe tries to detect your steps and their direction.
• Should you notice a drift in the path you walked, you can manually adjust its heading as well as the position estimate itself.
• Meet other reckonMe users and automagically exchange your estimates.

For the more technically inclined:

The approach is rather simple: Given a starting position (fix), one's current position can be calculated by advancing that position based on one's course and speed, i.e. the number of steps walked. This process is called dead-reckoning (from correct "ded" for deduced reckoning, DR) and has been used in marine navigation for centuries.

Once started, reckonMe evaluates your iPhone's gyroscope and accelerometer data in order to detect your steps and their direction. It does not rely on external data, such as GPS or any other infrastructure. Therefore, it is ideally suited for indoor positioning, where GPS is typically unavailable.

However, DR is far from perfect. Over time, the errors in the heading and speed estimates accumulate to ever-greater values. This is where collaboration comes into play: The error in an individual location estimate can be significantly reduced if these estimates are shared with others and combined.

While reckonMe is running, its current position estimate is constantly broadcasted using Bluetooth Low-Energy (BLE) to be picked up by other peers. Once a peer is close enough, its position estimate is incorporated into one's own estimate. Even though some individuals may be worse of after an exchange, the average systemic error shrinks as a location "awareness" emerges.