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Active 10 and Distance Recording

 
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goon525
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Joined: Aug 25, 2005
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PostPosted: Sat Jul 04, 2009 9:06 am    Post subject: Active 10 and Distance Recording Reply with quote

A couple of months ago I posted the experience I'd had on a short walking holiday on the Isle of Wight where it seemed to me that my Active 10 was over-recording distance on walks by about 7%.

After a recent trip to Leatherhead to have the GPS aerial retuned (successful, now averages only about a minute to get initial fix), this issue has become my only real area of reservation about the Active 10. And I've just had an interesting walking holiday in the Peak District, with a group that included one other Satmap owner, and two people using Memory Map, one on a PDA, and the other on a RoadAngel. There was a consistent, and large - up to 12% difference between my distance reading, and that of Peter, the other Satmap man. It seemed that he usually under-read by around 5%, while I was over-recording by 7% as before. The two Memory Mappers were smugly in agreement with each other, pretty much splitting the difference between us.

The only difference between the two Satmaps is that I'm running the latest firmware, and Peter isn't. But I'm pretty sure that my Active 10 over-recorded before I updated the firware. So do we have two bits of hardware, each at the limit of manufacturing tolerance - but in opposite directions? I'd be fascinated to know.

One final point of interest. At the end of each day's walking, Peter and I would 'Convert Trail to Track' - and my distance would fall, and his would increase, so that we virtually met in the middle, and have each ended up with a record of each walk that we can trust. But what on earth is going on here? I'm going to copy this post to Satmap support, because I really would like to know!
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davidor
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Joined: Nov 14, 2008
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PostPosted: Sun Jul 05, 2009 3:50 pm    Post subject: Reply with quote

My Satmap will also reduce the distance when converting the trail to track. I always put this down to the satmap faithfully recording all my little deviations and staggers, but when converting to a track it uses a longer point separation so removing all the lottle wiggles on the route. Perhaps the Garmin uses a wider point sparation to start with.

Doesn't explain the one that under records the distance though.
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Mike777
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Joined: Feb 12, 2009
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PostPosted: Mon Jul 06, 2009 8:15 am    Post subject: Re: Active 10 and Distance Recording Reply with quote

goon525 wrote:
I'm going to copy this post to Satmap support, because I really would like to know!


I have exactly the same issue so it would be good if you could post the reponse here.

Thanks

Mike
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planetnine
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Joined: Dec 11, 2006
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Location: Lincolnshire, England.

PostPosted: Mon Jul 06, 2009 12:07 pm    Post subject: Re: Active 10 and Distance Recording Reply with quote

goon525 wrote:
...One final point of interest. At the end of each day's walking, Peter and I would 'Convert Trail to Track' - and my distance would fall, and his would increase, so that we virtually met in the middle, and have each ended up with a record of each walk that we can trust. But what on earth is going on here? I'm going to copy this post to Satmap support, because I really would like to know!


Your A10 is doing as I would expect; it will slightly over-record due to meanderings within your walk (I'm not sure about 7% though) and this will convert to something closer to the actual route distance when the data is reduced to its "Track", possibly even under-reporting it slightly if a few corners are cut off.

Have you taken the "Track nn Raw.gpx" file from your map card and viewed it with Google Earth? does it look like a realistic walk or are there "spikes" or major deviations from the path trodden indicating GPS fix problems?

I only seem to get spikey spiderweb meanders when I've gone into a building and my A10 naturally has problems with accuracy, plotting a cats cradle of suppositions around the building in question, but any such spikes on your Tracks while outdoors would point to a possible problem with your unit's fix and go towards explaining your over-measurement.



this is a raw track from a walk in woodland to give an example, the blue trail diagonal bottom-left to top-right is about 650m long and includes stops for photos of insects, etc. The return path is much straighter. This was a Sunday afternoon amble with an expecting fiancee, rather than a serious distance-covering hike or route-march. It is also in woodland rather than open country and may include some data inaccuracy from foliage obstruction, although it seems to faithfully capture my meanders.




This shows fix errors while inside a building. These "spikes" should not appear on outdoor tracks; if they do, your GPS is struggling to maintain satellite signals.

Nathan.
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planet nine
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planetnine
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Joined: Dec 11, 2006
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Location: Lincolnshire, England.

PostPosted: Mon Jul 06, 2009 12:30 pm    Post subject: Reply with quote

I'm not sure about your colleague who is under-reporting the distance, I'd be interested in comparing yours and his raw gpx data files.

This Google Earth screen-capture illustrates the difference between A10 raw data and the "Track" that is produced from it, both are from the same walk, the blue line is the raw data and the red line is the reduced-data Track.



This might help understand the margin of error between the different measurements, although what mileage do you want? -the distance measured on the map or your actual route walked? From this picture you can see that a group walk will put meanders into the route (here queing to cross a stile and regrouping before walking along a road).
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planet nine
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Gibbo10
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Joined: Sep 21, 2008
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Location: Swindon, Wilts

PostPosted: Mon Jul 06, 2009 6:03 pm    Post subject: Reply with quote

When I know that I am going to stop in a location that may mean that I'm going to wander about for a while I use the stop recording option on satmap. If I go into a building especially ones that have the initials "P.U.B" above them I also press stop, then press start again when I'm ready to continue to walk.

Also, in Quo digital mapping software when i get back i run simplify route and that takes out some of the multiple waypoints.

I also wonder, but not tried it if you changed the the gps update from 1 seconds to 3 seconds if this would reduce the problem?
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goon525
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Joined: Aug 25, 2005
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PostPosted: Tue Jul 07, 2009 8:28 am    Post subject: Reply with quote

Happy to report that both Peter and I use 1 second interval between GPS updates. And I hit 'Stop' for major lunch and coffee stops, but not for pauses to cross stiles etc. I accept that a small amount of over-recording is probably normal (but why don't the Memory Map users seem to get it?) but nothing so far explains why I over-read by as much as 7%, Peter under-reads by 5%, and then it comes right for both of us when we convert track to trail.
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philpugh
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Joined: Dec 28, 2005
Posts: 2003
Location: Antrobus, Cheshire

PostPosted: Tue Jul 07, 2009 9:20 am    Post subject: Reply with quote

I've mentioned this before with respect to the STOP / START action on a SATMAP. Whilst its does stop the trip logging as far as the graphical display (i.e. the ascent/descent graph) and the trip info the RAW GPX data logging is not stopped (at least it doesn't appear to on mine running latest firmware). I have taken to switching mine off when stopping for lunch and switching it back on just before re-starting the walk.

I have not done any significant trials of distance errors but on walks where I have been logging the walk with logger as well as the Active 10 the difference in distances between the RAW tracklog data and the logger has been within 2-3% each time - nothing I feel I need to worry about.

My RAW tracklogs, when plotted onto 1:25K mapping on MemoryMap, places the tracks over the paths/roads (when cycling) that I have been on. Mind you this is true of my Colorado 300 as well!
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WalkerDan
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PostPosted: Thu Mar 11, 2010 6:45 pm    Post subject: Reply with quote

Having done a couple of walks with the Satmap i've just bought I'm also a little confused with the loss of mileage when converting a trail to a track. On longer walks with more stops for taking in the scenery and catching breath it appears to lose more than when on a non stop walk, but as the longer hill walks also include more ascent and descent I wonder if the conversion loses the distance made by the ascending and descending an only measures it as if it was a flat walk. I'll do some more checking but it would be useful to be able to bottom this one.
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planetnine
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Joined: Dec 11, 2006
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Location: Lincolnshire, England.

PostPosted: Tue Mar 16, 2010 2:12 pm    Post subject: Reply with quote

WalkerDan wrote:
Having done a couple of walks with the Satmap i've just bought I'm also a little confused with the loss of mileage when converting a trail to a track. On longer walks with more stops for taking in the scenery and catching breath it appears to lose more than when on a non stop walk, but as the longer hill walks also include more ascent and descent I wonder if the conversion loses the distance made by the ascending and descending an only measures it as if it was a flat walk. I'll do some more checking but it would be useful to be able to bottom this one.


Dan, see my last post with the red and blue trails above; this might help understand what is going on.
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