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Old September 25th 16, 08:16 AM posted to sci.geo.satellite-nav
Terry Pinnell[_3_]
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Default Puzzling change in trackpoint rate

Alan Browne wrote:

On 2016-09-14 15:35, Terry Pinnell wrote:
Seems fairly quiet here but I'm hoping that one of the resident
experts can help me get to the bottom of some odd behaviour please.
I've tried several GPS, iPhone and iPad forums but still have no
satisfactory resolution.

I can't understand why my iPhone 6S+ recently started recording many
more trackpoints than previously:
https://dl.dropboxusercontent.com/u/...Comparison.jpg

Most of those have used the Memory-Map iOS app on my iPhone (plus a
few on my iPad) but I get the same averages with another app, Pocket
Earth. So it's app-independent, purely down to the iPhone. Here's a
track I recorded today (with Pocket Earth), which (unlike the examples
in my table, which were all walking) include sections of waiting and
bus riding too.
https://dl.dropboxusercontent.com/u/...-Frequency.jpg

I'm still not sure if it's a good or bad thing! Unlike dedicated
devices, on this 128 GB iPhone I have no shortage of storage space. So
maybe I should be celebrating the unexpected availability of vast
numbers of trackpoints, instead of fretting about it!

But ... why would the rate have *changed* so greatly around early
July?


Perhaps it updates less often when there is poor quality in the position
solution. Where do you have the phone when you're recording such
tracks? (pocket?). When the points were more numerous did you have it
in a better position? Was it hilly or urban canyons? (The later should
have good cell aiding, however).

Even sat geometry could have an impact at the time that you're recording
on the position quality.

Just a guess.


Thanks Alan, and apologies for not acknowledging sooner.

There has been no change of those kinds at my end. Still carrying the
iPhone either in shirt pocket or (thin) trouser pocket. Same types of
terrain (mainly English countryside).

How about the satellite end? Could there have been some change there?

--------------------

More important (as the very high rate seems here to stay) am I right
that this significantly increases estimates of gross ascent and
descent? Elevation profiles chart now look very much noisier. Should I
just increase the smoothing factor until they 'sort of look right'?!

Opinions vary widely on this topic, including the 'fractal' view that
you can regard just about *any* estimate as 'accurate'. (Distance as
well as cumulative ascent/descent.) But I haven't given up on trying
to come up with reasonably realistic estimates, so that helpful
comparisons can be made, both about walks done and planned.

--
Terry, East Grinstead, UK