Max speed 26.6 mph when walking !

Mike777 · Regular Visitor Joined: Feb 12, 2009 Posts: 99

Hi all

I went on a long walk over the weekend and was surprised to see the trip log reported a top walking speed of 26.6 mph !

Don't rememder walking that fast.

Any ideas why this sould be the case

Many thanks

Mike

philpugh · Posted: Mon Jul 06, 2009 10:38 am Post subject:

Could be any number of things.

Not fully locked onto sats before setting off. This could cause a momentary change of position as the fix gets better - giving a false speed reading.

Poor sat reception (trees/concrete canyons etc) causing a similar 'misplacement' on the map - giving rise to an instantaneous rogue speed.

Worst I ever had was a tracklog position on my Garmin Colorado 300 that placed me off the Shetland islands when I was walking in the Derbyshire hills. It was one tracklog point - all the rest were correct. I think this one was caused by the unit being very close (same rucsac outside pocket) as my GPS datalogger. I keep them separated now.
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Phil

themib · Occasional Visitor Joined: Jul 13, 2008 Posts: 17

I can beat that!
I reset my log, went mountainbiking near fort william.
I was suprised to see my total distance correct around 22 miles, but a maximum recorded speed of 735 mph.

Now Thats fast in a Jet fighter!

davidor · Regular Visitor Joined: Nov 14, 2008 Posts: 117

It's one thing that diappoints me about the Satmap (apart from that awful wide orange route line). My speed seems to vary from 0 to 7 or 8 mph when I'm standing still! I've tried to use it to guage the speed of my boat on the canal, which should be about 3 mph. At a steady speed the figure is all over the place, and even the average speed doesn't look right. In contrast, my old Garmin eMap would give a dead accurate speed with no silly wandering. It would also stand still when I did. Really can't understand how Satmap let this go through as I've not experienced it with other GPS or sat nav devices.

philpugh · Posted: Thu Jul 09, 2009 5:47 pm Post subject:

A little 'wandering' is quite usual with most GPSr devices unless they have a facility to 'ignore' small changes - which usually renders them useless for walking. However with a decent number of sats (9+) locked in you should get very little in the way of wandering. I use mine for walking and cycling and don't have any issue with the speed display.

Is it taking more than 30secs in a warm restart? I.e. turn it off, wait 5 mins and turn it back on again. If it is taking a couple of minutes or so you may want to consider sending your Active 10 in for an aerial tune-up, this may help in getting a better spread of sats allowing a more accurate fix to be generated.

I've just set my Active 10 up with a deliberately degraded signal (5 sats in a 100 deg arc) by putting it in a window in the house. The house has roof and wall construction that utilises aluminium backed insulation - it's quite an effective radio blocker!

After 6 mins the position has not changed and the av and max speeds are still 0.0mph It is calculating a positional accuracy of 29ft. Perhaps your unit is in need of a tune-up?
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Phil

philpugh · Posted: Thu Jul 09, 2009 6:51 pm Post subject:

Update on crude experiment above.

I let it run for 1 hour.

After this time it recorded a distance travelled of 65 feet with a max speed of 3.5 mph. This appeared to be two 'one-off movements' caused by a sixth sat coming into view and then loosing one 15 mins later.

All in all a pretty good result. The position showing with 6 sats up (about 120 deg spread) is within 5 metres of the actual position according to the 1:2500 OS mapping we have for the farm. With 5 sats the position was within 20 metres.

I'll settle for that!
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Phil

planetnine · Posted: Mon Jul 13, 2009 10:40 pm Post subject:

TomDavison · Posted: Tue Sep 15, 2009 12:09 am Post subject:

I've yet to complete a walk where the max speed was anything near reasonable. I think the problem is as follows. Lets assume you walk at 3mph. In a straight line you are doing 4.4 ft per second. If the GPS were absolutely accurate, and recorded every second, the instantaneous max speed would be correct.

Now look at an accuracy of say 10 ft CEP. It could give a position 10 ft behind you and to the left. The next second it could be 10ft in front of you and to the right. A bit extreme, but it would then think you did a little over 20 ft in the second, which equates to around 14mph.

In calculating the average speed, over a distance of several miles, the speed error caused by a 20ft error over the total distance is so small as to be effectively zero.

I wait to be shot down on my theory.

philpugh · Posted: Wed Sep 16, 2009 9:24 am Post subject:

You have correctly identified the 'problem'. With the 'circle-of-error' being larger in poor reception conditions the rogue speeds can be 2 to 3 times what you calculated.
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Phil

Bosun · Posted: Wed Sep 16, 2009 10:15 am Post subject:

Another theory as to the incorrect maximum speed being shown on the Active 10 ,also waiting to be shot down.

During a walk there will perhaps be times when you remove the Active 10 from round your neck say,or take it out of a rucsac,or point quicly at something with the GPS in your hand.

Just for that second the Satmap may well be moving much faster than your walking speed and hence will give your maximum speed as very high.

Well it sounds OK to me anyway.

Ian

johno99 · Regular Visitor Joined: Oct 02, 2008 Posts: 80

Does this mean the total distance will be incorrect as well?

JimmyTheHand · Frequent Visitor Joined: Apr 16, 2005 Posts: 386

philpugh · Posted: Fri Sep 18, 2009 10:03 am Post subject:

philpugh · Posted: Fri Sep 18, 2009 5:57 pm Post subject:

Sorry for previous multiple replies (since deleted) - I was having major probs with the network and the page never refreshed.
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Phil

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