There may be times where a device is unable to acquire a GPS fix (for example it is indoors) but it can connect to the cellular network and upload it's data. When a valid fix cannot be acquired, Digital Matter devices will report the last known valid fix (and the timestamp of this fix will be reported with the GPS Data - Field 0). On top of this, a 3D Fix OK, and Valid Fix flag are contained with the GPS data (see integration documents for more details if using a 3rd party platform).
A challenge for an end software platform is identifying when a GPS fix is out of date - so end users do not automatically assume a recent device update/upload means the location is current.
Given what is sent in the device data software platforms can work out which fixes are 'current'.
GPS data is sent in Field ID 0, and the lat/long (position) has an associated time - GPS Time - this was when the fix was obtained.
Additionally, there is a Record Time, the time the record was taken.
If a fix fails when taking a record - the last known good fix (and the time of that fix) is sent to the server. So the Record Time will be more recent than the GPS Time. and the difference gives us the GPS Age.
"Unknown GPS Age"
In Telematics Guru, a GPS Age of 'Unknown' in the telemetry, means the GPS fix was achieved at the same time as the log record. (GPSTime = RecordTime)
The GPS Age and GPS/3D Fix OK columns are available in the Telemetry view (Assets >> Telemetry)
GPS Age is in general a more useful indicator.
The GPS age is displayed on the Live View pop up for an asset.
How to use GPS Age, and comments
GPS Age on Externally Powered Devices
Powered devices such as the Bolt, G62 and Dart2 do not send a new GPS fix to the server on heartbeats (i.e. when sitting stationary) The device turns on it's GPS each heartbeat (usually each hour by default) to download new aiding data and ephimeredes to speed up subsequent fixes, but the position from the end of the last trip is reported. Because of this behaviour, while parked the GPS age of a powered device will increase each heartbeat. As soon as a trip starts it should drop back to 0/unknown.
How to use the GPS Age indicator
The GPS Age indicator is most useful for battery powered devices reporting infrequently, where a missed GPS fix results in there being a long period of time passing without a position update. For example consider a device getting a position and updating this position every 4 hours, beginning 8am.
- 8am, successful fix and update - GPS Age is 0
- 1200, failed fix, update - GPS age is 4 hrs.
If a user was going to visit an asset (e.g. to service it), they can check the live view and GPS age before going out.
If you are regularly missing fixes - follow the steps in our GPS Troubleshooting article here
GPS Age in Telematics Guru
The GPS Age value is also available as a field in reports. By customising reports you can get GPS Age to show alongside other values for the logs.
The GPS Age column is available in Device Data Export and Device Telemetry export
You can also set up alerts to tell you when a device hasn't got a new fix in a set amount of time in minutes. Be careful when using this alert value condition due to how a device might not update its GPS fix when it calculates that it has not moved from a previous location (particularly powered devices as discussed above).
This is best used for early detection of issues with battery powered devices. E.g. send an Alert if my Oyster2s have very old GPS Age.