Inaccurate GPS?

mk1rob

Hi,
I've been using strava on my iPhone for a while but noticed it seems very inaccurate. I can do exactly the same trail but it will vary on distance etc every time. I looked into it and a dedicated GPS seemed to be the answer. So I've just bought a Garmin Edge 820 GPS but it still seems inaccurate when looking at the map. The pic below shows what I mean, where I rode is nowhere near the trail :? Is this just something I need to put up with or is there a fix? Ive heard turning auto pause off helps but its already off.

Thanks in advance

fenix

Have you checked the satellite view to see if the trails mapped there are correct?

rockmonkeysc

GPS isn't particularly accurate.
Me and a mate rode a 55.1 mile route according to my Garmin, his said we'd done 56,3 miles. I've seen other similar differences. I've also seen some ridiculous top speeds on rides.

cooldad

KOM on one of the sections I ride managed 249kph.

A little bit faster than me, so I believe it may be a mistake.

I also have a friend who managed an instantaneous trip to Algeria on one ride. We didn't even notice he'd gone.

larkim

GPS is bloody accurate. However, GPS receivers like phones, dedicated consumer devices etc etc are prone to losing elements of the signal due to obstructions (bodies, trees, buildings, hills). Some units handle losing signals better than others.

But if any MTBer can think of a better way to have a sub 100 pound battery operated piece of electronics track their route so that they can willy wave later about the precise details of their ride, there's clearly money to be made...

avalanche_expert

It's only acurate within 3 meters when I last looked into it. Also trees etc, can affect performance.

Like you the redline tracking my route often goes off course when you view the map later on. Also my bike computer will give me a different trip mileage and average speed compared to strava. It's not massively different, but it's rarely ever the same.

Also top speed achieved each time is miles out, I will occasionally hit 30 -32 mph, but usually it's the high 20's - strava usually says I've reached 40+ mph!

Something else which bugs me is the auto pause doesn't pause quick enough. I can stop off for a quick call of nature and not be moving for a good 15 or so seconds until it finally pauses.

One of my KOM's is also wrong as there is no way I could of completed this particular section in 29 seconds especially on the day I allegedly achieved it.

I do love strava, it's nice to track where you've been, who with and when. Now I have more than one bike due to also committing, I like tracking which bikes have done what too. But it's not a perfect interface by any means.

kajjal

Check how often your GPS device is logging your position. My garmin edge 500 is set up update every second some on default settings check a lot less so are less accurate. Even then mine has its moments but generally very good.

schmako

My GPS clocked me at 217mph at the weekend, I'm sure that was totally accurate..

But yeah I still find GPS interesting to look back at a rough time, distance, altitude and speed.

larkim

OK, OK, we can all point to times when our receivers haven't done a great job of accurately recording position. But for most of the time, for most of the leisure purposes we use GPS for it is mroe than capable of doing what we want.

In terms of overall accuracy, even if 3-3.5m is the level of precision taken for a single reading, modern devices are canny about smoothing some of those errors out, and averaging also helps - so if 1000 measurements are taken over 1000s of a ride, each with a precision of 3.5m, the distance between those two points at worst should be the actual, tape-measured distance plus 7m. Garmin's etc do a decent job of smoothing that path too when they compile the route together too.

I've used GPS since before Selective Availability was turned off, and greatly since (one of my lately passive hobbies is geocaching which requires using GPS devices to locate small things in the middle of nowhere). When the recorded coordinates are correctly given in the first place, my watch, my phone, my dedicated GPSr all get me to within about 1m of the actual object, assuming a decent view of the sky.

Give your device a clear view of the sky as much as possible, remove any powersaving options that restrict sampling rates etc and you'll find GPSs all work very well indeed. Unfortunately you can't always give it a clear view, especially when on a MTB, so there'll always be some limitations.

fenix

Did the OP wait for his GPS to get a proper lock before starting ? I know my wife is sometimes impatient with her phone and on the occasions she's started without waiting for Satellite lock her runs have been pretty wiggly - but you can still see where shes' been.

My Garmin Fenix follows my route perfectly as far as I've noticed.

fenix

Did the OP wait for his GPS to get a proper lock before starting ? I know my wife is sometimes impatient with her phone and on the occasions she's started without waiting for Satellite lock her runs have been pretty wiggly - but you can still see where shes' been.

My Garmin Fenix follows my route perfectly as far as I've noticed.

Tashman

I've had to revert to my old Samsung S3mini for my Strava recording. The HTC Desire 320 (shocking phone, avoid like the plague) zigzags me all over the roads and doubles my distance instantly

larkim

Interesting you should say that Tashman - my wife's brand new Moto G4 is noticeably poorer at smoothing out some of the erroneous stuff than her Moto G 1st gen was. Not such that it causes any real differences, but miles run on the old phone can now be c. 1.05m if she's unlucky with where the errors lie.

The best watch I had for tracking routes was a TomTom Runner - very smooth traces, with a high degree of accuracy. The Garmin Vivoactive which I use now is great, but now *quite* as great in trace terms as the TomTom was.

lostboysaint

Garmin 800 and Forerunner 610 both appear to be very accurate (based on both map overlays and time and distance calcs).

haydenm

Another thing to remember with mapping in general is that all map layers are data laid over a coordinate system so there is no 100% definitive version, it is possible that your GPS is extremely accurate but that area of the baselayer is distorted due to the way it was overlaid. Looking at that picture it seems reasonably accurate but has been 'shifted' slightly, it could be a GPS problem or a projection problem. Judging by the mapped routes at Glentress or Ae they never follow the bulk of GPS'd rides and often seem to be shifted out. At work I find that even things recorded with extremely accurate GPS devices are often 'out' when compared to different baselayers (like aerial photography or OS data) and conveniently the one which is most accurate is rather expensive from OS...