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sci.geo.satellite-nav (Global Satellite Navigation) (sci.geo.satellite-nav) Discussion of global navigation satellite systems (GNSS). Topics include the technical aspects of GNSS operation, user experiences in the use of GNSS, information regarding GNSS products and discussion of GNSS policy (such as GPS selective availability).

Puzzling change in trackpoint rate



 
 
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  #11  
Old September 29th 16, 11:30 AM posted to sci.geo.satellite-nav
Hans-Georg Michna
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Posts: 764
Default Puzzling change in trackpoint rate

On Thu, 29 Sep 2016 13:25:11 +0200, Hans-Georg Michna wrote:

Locus Map does all this, albeit only on Android. It can even
fill in the altitudes after the fact, using the SRTM (Shuttle
Radar Topography Mission, http://jpl.nasa.gov/srtm/ ) data, if
you put that on the phone. I have done exactly this to try it.
It works.


Correction: It does this even if you do not put the SRTM data
onto the phone first. It auto-loads the relevant data segment
automagically.

If you like your track to be enhanced with altitude values, send
it to me, I will do it on my phone and send the result back.

You will have to do a small and obvious correction to my email
address, by removing the NoEmailPlease.

Hans-Georg
  #12  
Old September 29th 16, 09:41 PM posted to sci.geo.satellite-nav
Terry Pinnell[_3_]
external usenet poster
 
Posts: 9
Default Puzzling change in trackpoint rate

Hans-Georg Michna wrote:

On Thu, 29 Sep 2016 13:25:11 +0200, Hans-Georg Michna wrote:

Locus Map does all this, albeit only on Android. It can even
fill in the altitudes after the fact, using the SRTM (Shuttle
Radar Topography Mission, http://jpl.nasa.gov/srtm/ ) data, if
you put that on the phone. I have done exactly this to try it.
It works.


Correction: It does this even if you do not put the SRTM data
onto the phone first. It auto-loads the relevant data segment
automagically.

If you like your track to be enhanced with altitude values, send
it to me, I will do it on my phone and send the result back.

You will have to do a small and obvious correction to my email
address, by removing the NoEmailPlease.

Hans-Georg



Thanks Hans, that's very kind of you. But I have so many such tracks
that it would be impractical.

Pity there's no equivalent iOS app, as Locus Map sounds excellent. My
desktop app, GPS Utility, supports LIDAR data as I mentioned
up-thread. But it requires manual download of the files, and many of
the 'tiles' are incomplete (void of altitude data). So it's rather hit
and miss.

What do you think of GE's elevation profile data? How does it compare
in accuracy to Lotus map?

And any thoughts on the cause of the subject under discussion?

--
Terry, East Grinstead, UK
  #13  
Old September 30th 16, 06:01 AM posted to sci.geo.satellite-nav
Terje Mathisen[_3_]
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Posts: 25
Default Puzzling change in trackpoint rate

Terry Pinnell wrote:
Thanks Hans, that's very kind of you. But I have so many such tracks
that it would be impractical.


Have you considered Gogle Earth (Pro is free now)?

I know that it by default will import GPX tracks and lock them to local
ground, so if you can import a bunch of tracks you should get altitude
data for all of them at once.

What I don't know is if the resulting KML/KMZ files will store that
altitude data or not, if they do then gpsbabel would be able to convert
them back to GPX.


And any thoughts on the cause of the subject under discussion?

Track point rates are typically controlled by an algorithm which tries
to minimize the number of points needed to generate a given
approximation to the raw (once per second or more) GPS measurements.

I.e. you store a track point each time the direction and/or speed changes.

I know that this is the way Garmin have handled it for many years, but
when I collect tracks of my orienteering races or when surveying new
paths, I always configure the GPS to a fixed 1 Hz logging rate.

A change on the same device without any reconfiguration on your part is
probably due to an update from the vendor which have tweaked the
filtering algorithm.

Terje

--
- Terje.Mathisen at tmsw.no
"almost all programming can be viewed as an exercise in caching"
  #14  
Old September 30th 16, 08:29 AM posted to sci.geo.satellite-nav
Terry Pinnell[_3_]
external usenet poster
 
Posts: 9
Default Puzzling change in trackpoint rate

Terje Mathisen wrote:

Terry Pinnell wrote:
Thanks Hans, that's very kind of you. But I have so many such tracks
that it would be impractical.


Have you considered Gogle Earth (Pro is free now)?

I know that it by default will import GPX tracks and lock them to local
ground, so if you can import a bunch of tracks you should get altitude
data for all of them at once.

What I don't know is if the resulting KML/KMZ files will store that
altitude data or not, if they do then gpsbabel would be able to convert
them back to GPX.


Thanks, yes! I guess you didn't see earlier posts and latest
screenshot?


And any thoughts on the cause of the subject under discussion?

Track point rates are typically controlled by an algorithm which tries
to minimize the number of points needed to generate a given
approximation to the raw (once per second or more) GPS measurements.

I.e. you store a track point each time the direction and/or speed changes.

I know that this is the way Garmin have handled it for many years, but
when I collect tracks of my orienteering races or when surveying new
paths, I always configure the GPS to a fixed 1 Hz logging rate.

A change on the same device without any reconfiguration on your part is
probably due to an update from the vendor which have tweaked the
filtering algorithm.


I still think that's the most likely (only?) explanation, despite the
fact that my local iStore claims there's been no change.

--
Terry, East Grinstead, UK
  #15  
Old October 15th 16, 09:03 PM posted to sci.geo.satellite-nav
external usenet poster
 
Posts: 7
Default Puzzling change in trackpoint rate

Terry Pinnell wrote:
I can't understand why my iPhone 6S+ recently started recording many
more trackpoints than previously:


Google Maps used to record more points when in the foreground than in the
background.

--
Clarence A Dold - Santa Rosa, CA, USA GPS: 38.47,-122.65
 




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