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A challenge for an end software platform is identifying when a GPS fix is out of date - so end users do not automatically assume a recent device update/upload means the location is current.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 implement a couple of methods to work out which fixes are 'current'
- Comparing the record time found in the record header - with the GPS time found in the GPS data field.
The record time will be when a GPS fix was attempted - if it failed, it will be older than this time. A difference of 5 min or greater may be of interested depending on your settings.
- Looking at the GPS fix flags.
Telematics Guru uses both methods.
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 here: GPS Troubleshooting