What is "Age" - Sure-Path GPS Boat Lane Tracking

Boat Lane Tracking
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What is the "Age" display?
An RTK Base station usually generates a burst of correction data (often called a packet) once a second and each packet is timestamped very accurately with the time it was generated. The packet is transmitted, usually via the internet, and eventually received by one or more RTK rovers.

The rovers are also gathering GPS data and generating position coordinates generally at a frequency of once a second but in the case of Sure-Path, ten times a second. The calculated coordinates are also very accurately timestamped.

If correction data is being received, it is used to increase the accuracy of the raw position coordinates. For any given set of GPS coordinates, the Age value is the difference between the coordinates timestamp and the timestamp of the correction data used to update it. Thus, the Age value gives an accurate indication of how long it is taking for a correction packet to go from the RTK base station, through the transmission chain and be received by the RTK rover.

So why does the Age value appear to be constantly changing? Well in the case of Sure-Path, base correction packets are being generated once a second but the rover coordinates are being generated 10 times a second. Thus, if the correction packet transmission time was say 0.2 seconds, the Age value would start at 0.2 just after a correction packet is received and then count up in 0.1 second intervals to 1.2 after which another correction packet would be received and the Age would drop back to 0.2.

If correction packets stop being received for any reason, the Age value will continue to count upwards until it reaches 60 seconds, at which point, the rover decides that the last correction packet is too old to be useful, and the rover will lose RTK Fix mode and revert to the basic GPS mode.

Why is the Age value useful in troubleshooting Sure-Path? As stated earlier, Age gives a good indication of how efficient the transmission method used for correction packets is and in the case of Sure-Path, this usually means the internet access method which could be WiFi or cell coverage or a combination of both. If the Age value stays below about 3 seconds, then all is good. If however, you notice that Age occasionally climbs to say 20 seconds and then resets, and this repeats every now and again, it means that although the transmission chain is adequate enough for RTK Fix mode to be retained, it may be worth looking at why the short breaks in transmission are occurring and find ways of improving it, especially prior to an important tournament.

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