GPS Position Jitter

GPS Position Jitter
GPS Position Jitter

Everybody seems to forget that those wonderfully precise GPS coordinates have an underlying error on the order of 20 meters, more or less, kinda sorta.

A friend took a bicycling vacation, riding about 50 miles a day, and camped overnight. Evidently his GPS tracker developed a nasty case of insomnia and wandered all over the campsite: the first two points might be actual motion, but the rest were in the wee hours of the morn when he says he was sound asleep.

It became painfully obvious over the course of his journey that you cannot depend on continuous satellite uplink coverage. Even though he was riding on rail trails and open roads, the every-ten-minute position uplink to low earth orbit would vanish for hours at a time. The GPS tracker has a 911 button, but it might be a long time before they could figure out where he was.

Memo to Self: get those GPS-to-APRS gadgets built for our bike trips…

2 thoughts on “GPS Position Jitter

  1. I rode 4300 miles in 2010 with a SPOT tracker. My experience was that many of the gaps in coverage are caused by antenna orientation. I found that placing the device on the top of my dear for best visibility to the southern sky minimised dropped tracking locations dramatically. The corollary is if you place it upside down it wont work at all. (and then you get phone calls because your family thinks you are dead ;) ).

    1. place it upside down it wont work at all.

      Aye, that’ll wake ’em up!

      The APRS network depends on line-of-sight VHF reception at many scattered nodes. Our bikes have mobile radio whip antennas mounted on the seat backs (barely visible there); they’re awkward, but we get great coverage anywhere around here. Coming out of the Lehigh River Valley in PA, though, showed that line-of-sight doesn’t work deep in a valley where Spot would probably see its satellite receivers.

      A friend of mine from college uses a Spot tracker on his cycling adventures, as well as on hikes. I enjoy seeing what he’s up to… but I’m glad he’s not depending on me to bail him out of a jam!

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