iPhone trackpoint interval?

terrypingps · Aug 30, 2016

GPS trackpoints with iPhone 6S
Roughly what is the average interval between trackpoints recorded on the iPhone 6S+ please?

What interval do others get between trackpoints with their iPhones?

My question is prompted by noticing an enormous increase in the number of trackpoints that my iPhone 6S+ is recording for recent walks/trips. I haven't pinned down the cause yet. Could be some mistake of mine, a setting or whatever, although I'm darned if I can see any on the iPhone.

(From March 2016 onwards the iPhone was in use; prior to that it was an HTC Touch Pro 2)

In particular, this huge number of trackpoints coupled with the inaccuracy of GPS altitude data makes a nonsense of any ascent / descent estimates derived from the resulting GPX file.

--
Terry, East Grinstead, UK

Nuvi-Nebie · Sep 1, 2016

I would say the number of trackpoints generated is controlled by the specific GPS App. that is running on the iPhone, rather than the iPhone itself, what App. are you using?

terrypingps · Sep 1, 2016

Nuvi-Nebie said:

I would say the number of trackpoints generated is controlled by the specific GPS App. that is running on the iPhone, rather than an the iPhone itself, what App. are you using?
Click to expand...

Thanks. I guess a little more background would have been helpful!

I use the Memory Map app on the iPhone to record the GPS data. So far I've found no way of altering the rate of this data capture, unlike many dedicated GPS devices and perhaps smartphones. As you see from the red examples in my table every GPS change is recorded, with a typical interval as brief as 2-3 seconds. Leading to very close points and therefore a large total number of them.

So a flat walk of one minute could result in a good estimate of distance, say 250 ft. But, because altitude estimates by GPS are very inaccurate, even for most dedicated devices, it would give a highly misleading estimate of gross ascent and descent, maybe over 100 ft a minute on my iPhone 6S+!

After transfer of the GPS file to my PC I open it in the desktop Memory Map application to display and work on it. From there I can save in the universal GPX format for work in other programs, such as Google earth, GPS Utility, etc.

Naturally, I emailed Memory Map too, but no response yet.

Also posted to the Apple forum, and had one reply advising that there was no provision for user setting.

--
Terry, East Grinstead, UK

Nuvi-Nebie · Sep 1, 2016

As you say most GPS programs that auto log track points have settings like 'every X feet', 'every X seconds' or a smart mode where the desision is made by changes in direction. Here is a help screen from Memory Map 2004 (desktop version), showing options for Minimum update distance (in Metres) and Track position interval (in seconds), I would expect to find something similar in the iPhone version.

If you can't get the iPhone version to do this, I would suggest using another logger App. that does have these options that creates a GPX output file

terrypingps · Sep 1, 2016

Thanks, appreciate your follow-up. I agree with your line of thinking. But I can find no setting in the iPhone/iPad Memory Map app that seems to make a difference. I'm hoping to get a reply from Memory Map soon.

As for the desktop settings, I have to assume they are intended for using a Windows laptop or notebook as the GPS device. I have occasionally added my iPad Air in its leather case to my rucksack, but cannot recommend it on a long walk! Those settings certainly make no difference after the event, IOW to my imported GPX files.

Getting more specific, I'd be very interested to know what you and other GPS users make of this walk from my iPhone 6S+ please.

https://dl.dropboxusercontent.com/u/4019461/20160826Clapton-B.gpx

It's the last track in the table I showed in my earlier post and has 4703 trackpoints, over 700 per mile. How many would others expect to record in a mile's flattish walking? What gross ascent/descent would you estimate from this file?

P.S. Surprised to find in a GPS Forum that GPX is not one of the many file types allowed for upload!

--
Terry, East Grinstead, UK

terrypingps · Sep 2, 2016

I've simplified my illustration:

--
Terry, East Grinstead, UK

Nuvi-Nebie · Sep 3, 2016

I would still suggest to you try out a different App. such as 'My Tracks' to see if it will allow a step size, it is possible to filter out the unwanted trackpoints afterwards, I have generated a new copy of your file with only 304 trackpoints by filtering on a mininmum of 100 feet between points, using Garmin Basecamp. The original has points that are as little as one foot or 1 second apart

Code:

Index . . . .Time . . . . . . . . .Altittude . .Leg . . L Time . . L speed . . Lcourse . . Position
1    26/08/2016 09:32:57     129 m            7 ft    0:00:02    2 mph    283° true    N51.88443 W1.75885
2    26/08/2016 09:32:59     129 m            6 ft    0:00:01    4 mph    159° true    N51.88444 W1.75888
3    26/08/2016 09:33:00     129 m            3 ft    0:00:02    1.0 mph    111° true    N51.88442 W1.75887
4    26/08/2016 09:33:02     131 m            11 ft    0:00:28    0.3 mph    122° true    N51.88442 W1.75886
5    26/08/2016 09:33:30     131 m            9 ft    0:00:23    0.3 mph    133° true    N51.88440 W1.75882
6    26/08/2016 09:33:53     132 m            2 ft    0:00:01    1.4 mph    103° true    N51.88439 W1.75879
7    26/08/2016 09:33:54     132 m            1 ft    0:00:01    0.7 mph    326° true    N51.88438 W1.75878
8    26/08/2016 09:33:55     130 m            0 ft    0:00:01    0.2 mph    305° true    N51.88439 W1.75878
9    26/08/2016 09:33:56     130 m            1 ft    0:00:01    0.6 mph    192° true    N51.88439 W1.75878
10    26/08/2016 09:33:57     130 m            10 ft    0:00:07    1.0 mph    306° true    N51.88439 W1.75878
11    26/08/2016 09:34:04     129 m            2 ft    0:00:01    1.2 mph    82° true    N51.88440 W1.75882
12    26/08/2016 09:34:05     129 m            1 ft    0:00:01    1.0 mph    107° true    N51.88440 W1.75881
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4687    26/08/2016 12:27:55     132 m            0 ft    0:00:15    0.0 mph    228° true    N51.88355 W1.75956
4688    26/08/2016 12:28:10     132 m            2 ft    0:00:01    1.3 mph    25° true    N51.88354 W1.75957
4689    26/08/2016 12:28:11     132 m            3 ft    0:00:01    2 mph    36° true    N51.88355 W1.75956
4690    26/08/2016 12:28:12     132 m            3 ft    0:00:01    2 mph    25° true    N51.88356 W1.75956
4691    26/08/2016 12:28:13     132 m            4 ft    0:00:01    3 mph    28° true    N51.88356 W1.75955
4692    26/08/2016 12:28:14     132 m            3 ft    0:00:01    2 mph    34° true    N51.88357 W1.75954
4693    26/08/2016 12:28:15     132 m            2 ft    0:00:02    0.7 mph    343° true    N51.88358 W1.75953
4694    26/08/2016 12:28:17     132 m            5 ft    0:00:02    2 mph    86° true    N51.88358 W1.75954
4695    26/08/2016 12:28:19     132 m            5 ft    0:00:01    3 mph    76° true    N51.88359 W1.75951
4696    26/08/2016 12:28:20     132 m            4 ft    0:00:01    3 mph    70° true    N51.88359 W1.75949
4697    26/08/2016 12:28:21     132 m            3 ft    0:00:01    2 mph    81° true    N51.88359 W1.75947
4698    26/08/2016 12:28:22     132 m            3 ft    0:00:20    0.1 mph    59° true    N51.88359 W1.75946
4699    26/08/2016 12:28:42     131 m            3 ft    0:00:01    2 mph    45° true    N51.88360 W1.75945
4700    26/08/2016 12:28:43     131 m            2 ft    0:00:01    1.0 mph    53° true    N51.88360 W1.75944
4701    26/08/2016 12:28:44     131 m            1 ft    0:00:01    1.0 mph    279° true    N51.88361 W1.75943
4702    26/08/2016 12:28:45     131 m            3 ft    0:00:01    2 mph    315° true    N51.88361 W1.75944
4703    26/08/2016 12:28:46     131 m                            N51.88361 W1.75945

The new version the GPX file is attached below

terrypingps · Sep 4, 2016

Thanks, appreciate your continuing help. But my focus is on discovering why the iPhone/Memory-Map combination has started behaving in this way. I can filter/reduce the number in various tools I have after the initial import, such as with GPS Utility or Memory Map itself, on the desktop PC.

I also now have Memory-Map's reply, which is essentially that they see no evidence that the cause is due to their app.

But I will try a test with a different app, probably Pocket Earth.

However, I am therefore coming to the view that it's a hardware or iOS problem with the iPhone 6S+. This thread seems to show that others are having recent problems too.

https://discussions.apple.com/thread/7504191?start=210&tstart=0

I was unable to download your GPX. Both links here failed.
[Moderator Edit]
The GPX file format is now uploadable to this forum and post # 7 has had the file attached

--
Terry, East Grinstead, UK

terrypingps · Sep 4, 2016

I gave it a try in IE instead of my usual browser, Firefox, and it downloaded OK.

At more than 15 times fewer than the original, your edit is probably getting a bit too light on trackpoints, but it's an interestingly arguable issue!

Here's the finished walk I used for my records and also a summary of the various estimates derived from various versions of that same walk:

Using original 4703 trackpoints:
20160826Clapton-B.gpx (circular)
Start 09:32, end 12:28, dur'n 2:55, 6.36 miles, avg. 2.2 mph, gross asc/desc 700 ft

Reduced in Mem-Map (PC) by a factor of 8:
20160826Clapton-B-589points.gpx
Start 09:32, end 12:28, dur'n 2:55, 6.03 miles, avg. 2.1 mph, gross asc/desc 430 ft
Google Earth elevation profile (no GPS data): gross asc/desc 383 ft

Converting original to a 299 waypoint route in Mem-Map gave gross asc/desc 403 ft

My best guess, for finished walk print out:
Start 09:32, end 12:28, dur'n 2:55, 6.2 miles, avg. 2.1 mph, gross asc/desc 400 ft

Your edit, 304 trackpoints:
20160826Clapton-B-100ft.gpx
Start 09:32, end 12:28, dur'n 2:55, 5.82 miles, avg. 2.0 mph, gross asc/desc 340 ft

My conclusion so far is that the original recording for some inexplicable reason captures a greatly excessive number of trackpoints compared to earlier recordings. That results in a significantly exaggerated gross ascent/descent, based on other evidence, personal 'feel', etc. And also a smaller exaggeration in distance. But it's then unclear what reduction is necessary to get the 'most realistic' estimates of distance and ascent/descent.

--
Terry, East Grinstead, UK

Nuvi-Nebie · Sep 4, 2016

terrypingps said:

I will try a test with a different app, probably Pocket Earth.
However, I am therefore coming to the view that it's a hardware or iOS problem with the iPhone 6S+.
Click to expand...

My money would still be on the App. rather than the iPhone. smart phones, PDAs, tablets etc. that have GPS use a stand alone GPS module, once turned on the module outputs a string of data containing, time/date, altitude, number of satelites in use and location every second, no decisions are made about the content of the data. So it would be up to the App. to decide how often this one second data is used, I can't see how the iPhone can play a part in the sample rate.

If you can get another App. to do what you want, it will prove the iPhone is not the problem, did Memory Map say if it was possible to change the time / distance of each sample?

I have edited # 7and # 8 with details of GPX files

terrypingps · Sep 8, 2016

As you suggested I tried a different app. In fact I ran both simultaneously and have summarised the result in a new thread 'Why this result?' as it might raise other issues.

The trackpoint recording rate reported by both apps is still very much higher than I''d expect, which IMO seems to make the iPhone the cause. But I'm far from sure and would welcome your views please.

Here are the two files:
https://dl.dropboxusercontent.com/u/4019461/20160908ForestRow-MM-B.gpx
https://dl.dropboxusercontent.com/u/4019461/20160908ForestRow-PE-B.gpx

Here's a summary:
https://dl.dropboxusercontent.com/u/4019461/GPS-SameDevice-DifferentApps-Summary.jpg

And an extract of detail from both:
https://dl.dropboxusercontent.com/u/4019461/GPS-SameDevice-DifferentApps-DetailExtract.jpg

--
Terry, East Grinstead, UK

Nuvi-Nebie · Sep 9, 2016

Very strange, the Pocket Earth track points are even closer together and the total number of points would be greater than the Memory Map version if it wasn't for the gaps. I can't try this App. as I only have Android devices and Pocket Earth seems to be iOS only, is it possible to set the sample rate in Pocket Earth? i.e. sample every X Seconds or every X feet / Metres?. I can't really explain the gaps in the 'PE' track, but it is possible that running both Apps. at the same time causes a 'race' for data with the MM App. winning the race. One possible test (although it won't be easy), would be to walk in a dead straight line, if possible due North, South, East or West to see if you still get a waypoint every few feet, the theory being that every change of direction is being recorded

terrypingps · Sep 9, 2016

"Very strange, the Pocket Earth track points are even closer together and the total number of points would be greater than the Memory Map version if it wasn't for the gaps."
No, MM still had significantly higher frequency of logging on that walk! (Hence the roughly 50% difference in total number of trackpoints. The distances differ by under 3%.)

But the PE rate is still far above the 'old' MM rate I was getting.

"Is it possible to set the sample rate in Pocket Earth? i.e. sample every X Seconds or every X feet / Metres?"
No settings of that sort in PE.

I raised the isssue in the iPhone/iPad forum a while ago but no useful discussion emerged.

The focus areas for me are:

1. I'd like to find iPhone users with a GPS app installed to learn if they too have seen a major change in logging rate.

2. 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 availabilty of vast numbers of trackpoints, instead of fretting about it!

--
Terry, East Grinstead, UK

iPhone trackpoint interval?

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