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Archive for May 17th, 2015

Bicycle GPS Track: Diggin’ Deep and Flyin’ High!

At first glance, I thought Mary had taken a tour of The Great Swamp south of the Vassar Farm gardens:

APRS Bicycle Tracking - Flying High

APRS Bicycle Tracking – Flying High

Having helped put the fence up, I’m absolutely certain nothing growing in the garden could get her to 4373 feet, much less boost the bike that high.

Before that, it seems she did some high-speed tunneling:

2015-05-10 18:17:31 EDT: KF4NGN-9>T1TP4X,WIDE1-1,WIDE2-1,qAR,KB2ZE-4:`eP}nAIb/"/k}
   type: location
   format: mice
   srccallsign: KF4NGN-9
   dstcallsign: T1TP4X
   latitude: 41.67466666666667 °
   longitude: -73.88283333333334 °
   course: 345 °
   speed: 42.596 km/h
   altitude: -371 m
   symboltable: /
   symbolcode: b
   mbits: 101
   posresolution: 18.52 m
   posambiguity: 0

The bike’s altitude began falling while she was on the way to the garden, from a reasonable 66 meters on the entrance road, bottoming out at -371 m as she hit 42.6 km/h (!), rising to 1341 meters with the bike leaning against a fence post, and returning to 53 meters as she started riding home.

Obviously, you shouldn’t trust consumer-grade GPS tracks without verification: it can get perfectly bogus numbers from fixes with poor satellite geometry. Altitude values tend to be only close, at best, even when you’re not too fussy about accuracy.

We experienced small-scale jitter in New Jersey and a friend carrying a commercial satellite link experienced similar randomization. Trust, but verify.

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