A Question About GPS

Did you know that GPS units can sometimes take several minutes to get fixated on your position?


Hi Ben, thanks for quick reply, one more thing my GPS thinks I’m in Sydney, how do you get it to Auckland?


It?s true. Just like we humans have those wrong side/right side of the bed mornings, GPS units have what they call ?cold starts?. If the unit has been turned off for a long time, or was last turned on in another part of the world (like Sydney, although as a New Zealander I do wonder if Sydney is on another planet), it will be forced to do a cold start.

GPSsatelliteIf you?ll allow me to divulge in some geekery for a moment? A GPS works by using precise timing to measure the time it takes to receive signals from several satellites. The longer the signal takes, the further it has travelled, allowing the GPS to triangulate its position. Just like a tiny electronic pirate map ? perhaps you could singe the edges of your GPS receiver for extra authenticity? The GPS also has what is called an ?Almanac? to initially guess which satellites to look for, and ?Ephemeris? for more precise information. This information can get out of date quite rapidly, so under normal conditions the GPS receiver will download this information occasionally in between receiving the location signals.

When you?ve moved across the world, or have been awakened by the kiss of a prince, the satellites above your head will not be the ones you expect to see. In this case, Sleeping Beauty will need to wait patiently until three or more satellites have completed sending their Ephemeris data, or in a really bad case, the Almanac as well. If you are under trees, inside, or driving along at speed, you?ll find this process takes longer than if you wait patiently under open skies. In some cases it can take more than a couple of minutes.

Perhaps use the time to meditate on your place in the cosmos. Update your internal almanac, grasshopper.

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