How the Oyster/Oyster2 Determines Location

The GPS module scans for GPS satellites and uses aiding data to determine its position, as per Digital Matter’s other devices. 

The Oyster will check in with a ‘heartbeat’ upload if there has been no activity for some time – typically once or twice a day. 

How the Oysters Detect Movement

Standard Movement Tracking Mode: 

  • The Oyster waits in a low power sleep state for accelerometer activity.
  • Once woken, it checks the GPS for movement. 
  • If the GPS shows movement over the start threshold, a trip is started. The start point is immediately uploaded to the server. 
  • The Oyster then resumes sleeping, with both the GPS and mobile data off. 
  • During the trip, the Oyster wakes frequently according to the logging period value, records its position, and checks for continued movement. The Oyster uploads a batch of recorded positions as determined by the upload period value.
  • Once the asset has been stationary for some time, or the GPS signal has been lost for some time, the trip is ended, and a final upload is performed. 

In addition, the Oyster2 will check in with a ‘heartbeat’ upload if there has been no activity for some time – typically once or twice a day.

Jostle Mode: 

The Oyster uses its accelerometer to detect movement, and trips are started/ended based on accelerometer movement rather than GPS movement. Usually, jostling is a trigger for a GPS check, and this determines a trip. It gives very robust trip tracking but cannot track very short trips. In Jostle Mode:

  • Accelerometer wakes the unit
    • By default, a wake filter is applied. The filter only starts a trip when it has seen 1 second’s worth of above-threshold movement in a 4 second period, or repeated short movements over several 4 second periods. Disabling the filter results in any accelerometer movement above the Wakeup Threshold (in Accelerometer Settings section of System Parameters) waking the unit.
  • Unit immediately determines it is moving – this is equivalent to entering a Trip for other DM devices
  • Once moving, the accelerometer no longer wakes the unit
  • It wakes every two minutes on a timer, and does two things
    • Asks the accelerometer if there was any movement in the last 2 minutes
      • If it is time to log a position, it gets a fix and records it
      • Once the accelerometer claims there has been no movement for a while, the default is 5 mins (Movement End Time parameter), the device decides movement has stopped.
      • The GPS version will also wait until the speed reported by the GPS has dropped to 0, to prevent movement ending when the movement is very steady and constant – e.g. a train where acceleration is minimal

Uploading can happen before, during and after movement, optionally. The default is before, after, and no uploads during movement.

Periodic Tracking mode:

This option disables trip tracking. In this mode, the Oyster no longer wakes up in response to jostling in order to check the GPS for movement. Instead, it will stay in a low power sleep mode until the next scheduled heartbeat. For applications that only require low frequency tracking of the final location of an asset, this mode gives the ultimate battery life.