Satnav (In) accuracy.

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tighterse
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Satnav (In) accuracy.

Postby tighterse » Sun Mar 12, 2017 7:21 pm

I was out today collecting my season ticket for the local loch. While I was there about 20 members of a local cycling club dropped in for a break and began to compare results from their various satnavs. Some had proper devices but most were using mobile phone apps.

What surprised me was that no two of them agreed. In fact some of the differences were shocking. What they thought was a 20 mile trip was anything from 17.5 to 20.8. One of them showed me a spreadsheet on his phone that he has been keeping for two years now. One of his regular runs of about 25 miles never records the same distance twice and the in trip is usually shorter that the out trip. He puts the error down mainly to hills but also to several 90 degree bends.

The general feeling is that satnavs should not be trusted to record accurate distances and are no more than useful guides. Some of them have also checked using satnavs in their cars and once again the recorded distances vary.

Has anyone on this forum carried out checks on satnavs?
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OldToot
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Re: Satnav (In) accuracy.

Postby OldToot » Tue Apr 25, 2017 7:56 am

In theory GPS can be very accurate indeed, which is how Western leaders can fight wars with "the bravery of being out of range" as Roger Waters has it. Or is that using lasers?

Any how, in consumer products it isn't very accurate really. If you have a Garmin sat nav in the car you can get an accuracy measure by pressing and holding in the top left corner - after a few seconds it will bring up a list of satellites it can see and give an accuracy measure. The best I've seen on mine is accurate to about 30 metres, I think.

Phones, of course, are so multi purpose they're not very good at anything, and are even less accurate - but like dedicated sat nav units, they are as good as they need to be.

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frv
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Re: Satnav (In) accuracy.

Postby frv » Fri Apr 28, 2017 10:15 am

The sat nav in my car is pretty consistent- no more than 0.1 miles difference on the same commutes. Accuracy however, now that's a different kettle of fish :lol:

I'm under the impression that Google Maps is pretty accurate and my sat nav compared to Google is also within 0.1 miles - maybe this is due to the fact my sat nav is built into the car and has decent maps and it's relying on this distances and not the inaccurate one's it's experiencing.

I have noticed that the odometer in the Audi reads about 0.3 miles less for the same in-bound commute compared to my old Honda over 22+ miles so there are inaccuracies there too!

If I'm cycling, walking or running using my mobile phone and the Strava App, for me it's also pretty accurate compared to a Google Maps but I know other people who may use a Garmin device or a different phone and they definitely get different results.

I also saw a program on tv where lots of people had wearable devices, did the same climb up and down some stairs multiple times and the differences were astounding so they can only really be used as a guide.
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tighterse
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Re: Satnav (In) accuracy.

Postby tighterse » Fri Apr 28, 2017 2:03 pm

The one thing I have heard is that changes in elevation and sudden changes in direction can be a problem. This was explained to me by example and I must say it sounds convincing. Take a piece of rope and accurately measure it. Lay it out between two points in your garden. Then introduce some "hills or mountains" using boxes or what not. The "road" distance between the two known points is now longer. Then introduce some sharp and short bends. Once again the "road" distance between the two known points is longer.

I've never used a satnav or a phone app, I've never had any need to so don't take anything I say as gospel.

Maybe we should get Frv on his bike among some of our mountains. Even in our local hills there are a few 1 in 5s and 1 in 6s. Then again Fettercairn to Banchory could be a good test; it's only 50/60 miles and he can knock that off in a couple of hours.
Kia Ceed 1.6 crdi isg Retired undefeated on 25,720 miles and 62.91 mpg overall

Now driving my second Sportage.

Warning. May contain a nut.

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