Is a dedicated GPS more accurate than a phone

mrs rocket uses her iPhone 6 + Strava as a running/biking/hiking diary. No so much for segments/leaderboards/training it’s just a record of where’s she’s been how far/fast etc

Depending on the terrain an error of 10% in distance/elevation is not unusual. Sometimes the phone loses the GPS, sometimes Strava straightlines zig zags and smooths out mellow inclines. Straight-ish routes out in the open seem fine but otherwise it lacks accuracy

Would a dedicated cycle GPS be better?

Yes IMO.

Yes dedicated GPS are surperior IMO. I find they capture the signal/location quicker, not sure if that’s the gps chip or the ariel but it’s easy to believe the phone gps chip is a compromise. As for elevation if you ever look at the data in a GPX file you can see that jumping up and down even on the flat, to be fare the custom GPS are susceptible to this also.

Yeah usually much better, especially under dense vegetation.

IME depends.

My Nokia e71 was very accurate, more so than my current Garmin 200 – and so is my iPhone 4. The Belkin’s I had seem very good.

But, my pals Garmin 800 series (with a Barometric Altimeter) seems very accurate.

Someone in our club did her masters thesis on this. The answer, if I recall correctly, is yes a dedicated unit is much more accurate. Something to do with how often the GPS signal is sent and received or something.

A dedicated unit is much easier to use, less faff too. Aldi were doing edge 200 for £65 or something like that.

Not necessarily TBH.

iphones are pretty accurate as it happens, they have access of both DoD GPS and GLONASS (from 4S and above), and routinely come top of accuracy charts, some of the newer Garmin devices aren’t that good surprisingly space being compromised for battery life and doing other stuff.

Yes dedicated GPS are surperior IMO. I find they capture the signal/location quicker,

I absolutely agree a dedicated GPS is better, but the one area a phone should always be better is in speed of initial lock-on due to their use of A-GPS.

One reason I prefer a dedicated GPS is I can set it to per-second recording for better accuracy.

The one time I used a phone and GPS for Strava at the same time the phone came out with quicker times so some people might consider the phone “better” for that reason!

Comparing my Garmin 510 and 2nd gen Moto G I’d side with the former being more accurate. The Garmin has a high-sensitivity receiver and can access GLONASS (Russian satellite GPS) whereas the Motorola has just A-GPS.

There’s a 200 ft elevation discrepancy between my HTC recording with strava and my garmin 510 on my 10 mile ride to work with 1100ft of climbing.

Phone under reads.. Or garmin over.. Not sure which.
Distance is the same recorded on both.

I use both and what they said about height gain is true for me as well.
GPS is better, losses coverage less often and gives a more accurate reading

Also lasts a hell of a lot longer as well when in use and its waterproof

Motorola has just A-GPS.

A-GPS helps on getting a signal quicker and provides the phone with a “star map” of satellites, most decent phones these days have access to GPS and GLONASS.

EDit, that means that a device with access to the local cellular network will “see” satellites faster than a device without access, and will get information about where the local satellites are. It depends on the phone/device whether it sees both or just one system of satellites. GPS signals are down to about 10m error on both accuracy and locality, I’ve no idea about GLONASS.

Garmins and phones usually poll at the rate of 1hz, which is ok for riding/mountain biking. A dedicated standalone GPS unit can refresh at 10-20Hz, depending on the type, giving a more accurate reading.

Satellite devices need to Accurate, but they also need “trueness” and “precision”

Imagine a archery target, a measure of precision is a nice little group of hits all in the same place, might not be bang centre, but they’re not scattered all over the place. Trueness is a measure of how close to the bullseye they are, might be all around the circumference of the target, but they all “hit centre”

accuracy is cover, weather, number of satellite, dependant.

Most devices win in some ares lose in others. (obviously) you need to work out what’s most convenient for you, nearly all of them are OK for running or mountain biking

Standalone GPS units handle elevation much better than phones because they tend to an altimeter of some description built in (barometric or some other method).

Phones can sort of get height info if they have enough of a GPS lock, or by using an altitude map, but it is a lot less accurate.

Phones do have some advantages though. Quick lock through A-GPS, the ability to flick through a variety of maps (Google,Bing,OSM,OCM,OS) and the ability to transmit – allowing your missus can track your position (if you want) and automatically upload tracks to Strava/Endomondo/etc

strava app samples GPS every 4s, I use the wahoo fitness app that samples every second. I think it does a pretty good job, it captured this moment of indecision pretty well:

Where you carry your phone makes a massive difference, side pocket and you are reducing the sky view massively, top pocket of bag or back pocket of jersey and the tracking is pretty good.

I suspect you’d see little or no difference between phones and dedicated (eg Garmin) GPS units. Ultimately they’re probably the same or very similar mass-produced GPS receivers.

Compare that to a WAAS-EGNOS assisted standalone unit and you’ll see sub-cm accuracy.

Where you carry your phone makes a massive difference, side pocket and you are reducing the sky view massively, top pocket of bag or back pocket of jersey and the tracking is pretty good.

Yep, bar mount works the best (but a bit exposed if you are off-road and prone to tumbles).

Barometric altitude measure is close to useless TBH, they rely on being calibrated often, and you do take account of the air pressure each time you use it, right? 😀

NASA and USAF maps are stored by the GPS, so unless your local hills have had the top knocked off or has been developed or built on in the last say..20years? It mostly depends on what formulas it’s using for smoothing, and how often it drops the signal. One test I saw (running around a race track) had altitude variants of +/- 100ft on the same device.

Edit: What Flaperon said

they rely on being calibrated often, and you do take account of the air pressure each time you use it, right?

I thought (and could well be wrong) that they have “known” height points so they self-calibrate when near one of those? And air pressure is sort of taken into account by it all being relative to the starting pressure?

I’ll quite often leave home at an indicated 90m above sea level and arrive at work at an indicated 50-100m BELOW sea level! Oddly enough, that’s not actually correct, but my Garmin (800) does it on a regular basis. I can even stand still and watch myself ‘descending’ at 1m every few seconds.

Unless your GPS (dedicated or phone) has a barometric altimeter built in, elevation data will be wrong, and as pointed out above baro-alti needs calibrating to retain its accuracy (though relative ascent and descent will be broadly OK).

Unless your phone is a disaster zone for GPS (and some are / were) the reality is that most devices are more than accurate enough for the purposes of giving measurement data about long and time consuming exercises.

There is always a better GPS, just as there is always a better bike. But most are good enough.

I ride with one of these just to be sure of that KoM…

Accuracy is similar, sample rate is higher for dedicated devices. That means it more accurately represents a ride. Also means battery might not last as quickly though. My Polar GPS watch wouldn’t last as long as my phone would using Strava; partly because of smaller battery, partly because of the demands of tracking position.

Regarding earlier comment on phones locking on faster because of AGPS, many GPS devices (mine included) use AGPS too and update satellite predictions when you sync.

Barometric altitude measure is close to useless TBH, they rely on being calibrated often, and you do take account of the air pressure each time you use it, right?

+1 I’ve no idea if there’s a way to improve it, but if I go out for a long ride in the morning/evening the elevation profile can be an almost constant climb/decent. i.e. the exact opposite of this:

Unless your GPS (dedicated or phone) has a barometric altimeter built in, elevation data will be wrong, and as pointed out above baro-alti needs calibrating to retain its accuracy (though relative ascent and descent will be broadly OK).

At least the GPS elevation will be +/- 20m (and averaging out over time unless it’s a very steep hill) rather than 300m out because it’s 8:30 in the morning.

IME the accuracy is as much to do with the devices location as anything else. STRAVA on my phone on an armband or jersey pocket seems to be the most accurate, followed by my Garmin 800 on the bars (which is obscured by my torso), followed by STRAVA in a camelback obscured by pumps, tools, sandwiches in tinfoil etc. Strava/phone in a back pocket is accurate enough to pick up weaving in and out of traffic IME.

Unless your GPS (dedicated or phone) has a barometric altimeter built in, elevation data will be wrong,

Not necessarily, GPS altitude data depends on what topography it uses, most (if not all) use the NASA SRTM (Space shuttle Radar Topography Mission) which covers the entire globe with altitude data and is accurate to about 90m to latitudes of about 60deg.

I wouldn’t rely on Barometric altimeters unless they’re calibrated That Day, and even then as you go up, pressure changes, and if the weather changes…

Biggest thing for me is battery life.

Nexus 4 with GPS on = not very long

Etrex with a couple of AAs = several days of use.

Biggest thing for me is battery life.

On long (road) trips I use a little tri-bag and stick an external battery pack in one of the side pockets with a short USB lead running to the phone mounted on my bars. That way I can record an all day ride and still have full phone charge.

Would a dedicated cycle GPS be better?

The definitive answer is “maybe, it depends”.

Try keeping the phone somewhere else for starters, jersey back pockets give a good view of the sky with no bag on, or near the top of a bag. A dedicated bar mount might have a better view, so it might be better in that respect.

As others have mentioned, frequency of recording may vary, but different apps will let you control that. And it depends how wiggly the trails are.

In general, GPS is a lot worse than people think – speaking as someone who uses it (and develops other localisation sensors) professionally.

An iPhone 6 (and anything else relatively recent/high end) will have a barometer in it, maybe not absolutely accurate but they’re decent relatively, so height “change” can be captured ok.

Biggest thing for me is battery life

latest iOS allows GPS use in airplane mode. I would expect android to be the same. i tracked ~10hrs of GPS + Bluetooth speed/cadence/HR/RFLKT display with about 30% battery left at the end of the day.

Ok thanks fellas it seems as though the iPhone may not be fundamentally inaccurate but results may vary. We live in a fairly poor area for cellular coverage and the mrs spends a lot of time running though woods 🙂 so maybe a proper GPS wouldn’t be that much more accurate

Hmm…

Also bear in mind that the original users of GPS the USNavy and USAF didn’t really need super accurate altitude data from it the USN especially for obvious reasons!

The USAF smoothing algrothims that some units use are also the reason your track sometimes goes through buildings…It’s expecting you to be airborne 🙂

Rocketman the times I’ve used strava on my iphone vs a Garmin 210 at the same time, the variables aren’t really that big a deal, it just comes down to convenience. My Garmin is easy to wear, shows heart rate, and syncs pretty well. The iphone loads automatically.

six of one, half dozen of the other.