# Accuracy - iPhone 4S vs Garmin 500



## duffin (Jul 25, 2011)

I did a search in this forum to try to find real data that shows the *iPhone 4S *GPS is not as accurate as *Garmin 500 *or visa versa.

I use mostly Strava and my ride group has a lively debate on this topic, but no one has data to back their argument.

Anyone?


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## Harold (Dec 23, 2003)

For the phone it will vary from app to app because any half decent app heavily massages the raw gps data from the chip and they all have their own algorithms for it. 

You don't see data because it is not easy to make direct comparisons.

I have some ideas how I would do a test that would explore different aspects of the phone's gps but I don't own one so it's a pointless question. 

Suffice to say that the raw data from the cheap gps chip and tiny antenna is junk otherwise there would not need to be any software massaging.

Geocachers have a better handle on the fine details and it is clear that phone gps receivers in general are less accurate. Still functional but the phone users often have a more difficult time.

I could run a pretty good test for you if you could send me your iphone


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## duffin (Jul 25, 2011)

NateHawk said:


> I could run a pretty good test for you if you could send me your iphone


I would if I wouldn't go broke not selling from my phone. 

iPhone 4S is supposed to have updated GPS chip.

What are we talking about - approximately 20% difference or 1% difference in accuracy?


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## edubfromktown (Sep 7, 2010)

I use Cyclemeter on an iPhone 4 and find it is generally off ~10% as compared to others with Garmin's. It is consistently off which works for me  Tried Stava long ago and didn't like having to pay a subscription fee to post more than 5 rides a month and it also was taxing on the battery by comparison.


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## cdouble (Jul 24, 2007)

I think there may be something to this. Some receivers have features like DGPS (differential GPS) or WAAS (wide area augmentation service) that improve accuracy, sometimes at the expense of taking longer to acquire the satellites. I don't know about the Garmin 500, but I do know my 8 year old garmin has WAAS, does take longer to startup than the GPS on my Android phone, and is more accurate...

cdouble
http://mo7s.blogspot.com


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## Harold (Dec 23, 2003)

yeah, WAAS is a type of DGPS system. and it does help a lot when available. I toyed around with disabling it on my Oregon to see if it improved battery life, but the degradation in GPS reception wasn't worth any small runtime improvements.

it's not the only DGPS system out there, but no consumer level GPS receivers use them. I SO wish I could get my hands on a sub $500 handheld that connected to real-time corrections from ground stations.

I have seen some tests using a 3GS compared to a few handhelds and for a SINGLE point, the iphone on occasion said the person was as far as 50ft away when right on top of the location, whereas various dedicated handhelds were anywhere from 9-20ft. The handhelds alternated between which was closest, but the iphone was always the farthest away. When you are doing a track, that error will occur at every track point and there are hundreds to thousands of points per track. This is where the data "massaging" comes into play on phone apps to reduce the amount of error displayed on the track.

The problem with phone GPS chips is that they do not use the same ones you find in your handhelds (Mediatek, SirfStar III or IV). I have never seen the brand/model of a phone GPS chip mentioned in product literature except for ONE read about available in Europe that was ruggedized and contained a Sirf III chip. Think about it, a complex touch screen GPS with a camera and a high sensitivity receiver costs $400-$500 and it doesn't have a flashy OS, gobs of memory, Gorilla Glass, wifi, cellular, Bluetooth, the ability to play music and movies, games, or any of that. Put a high sensitivity GPS chip in a phone and it'll jack up the cost significantly. Plus, with all the other hardware crammed into a tiny case, you couldn't fit a respectable-sized GPS antenna in a phone without bulking it up significantly.


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## icycle (Apr 20, 2004)

NateHawk, I've been looking at more accurate GPS add-ons for my iPhone 3GS, this one is very well rated and has all you're looking for:
https://www.emprum.com/ultimategps.php

MTK chipset, claimed better than sirfstar
DGPS via WAAS, etc
51 sat channels
5Hz update rate
etc

I'm going to start a new thread looking for feedback on this and some other similar devices.

Update: sorry, I reread the above and see that you don't have an iPhone/iPod. But, for those that do, or would be willing to buy, this seems like a great add-on.


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## Harold (Dec 23, 2003)

Oh there are plenty of add-ons to improve gps accuracy for phones (or give gps capability to things like laptops).

I do have an ipod but have no desire to turn it into a gps


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## duffin (Jul 25, 2011)

icycle said:


> NateHawk, I've been looking at more accurate GPS add-ons for my iPhone 3GS, this one is very well rated and has all you're looking for:
> https://www.emprum.com/ultimategps.php
> 
> MTK chipset, claimed better than sirfstar
> ...


Well, I started the thread and question and do have an iPhone and find this a cool alternative to use instead of toting Garmin and iPhone.

Now we just need a guinea pig who knows how to test it against the Garmin.


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## icycle (Apr 20, 2004)

duffin said:


> Well, I started the thread and question and do have an iPhone and find this a cool alternative to use instead of toting Garmin and iPhone.
> 
> Now we just need a guinea pig who knows how to test it against the Garmin.


duffin, good to hear. I started a thread you'll probably be interested in:
http://forums.mtbr.com/gps-hrm-bike...ht-iphone-gps-add-vs-new-handheld-771627.html

Several of my riding buddies have Garmin 500's. I will definitely be getting one of the solutions listed in my thread, first post. When I do, I'll be sure to compare tracks against the 500. I have lots of GPX tracks from their 500s already, downloaded from the Garmin Connect site.

As for a more scientific test, I'd be happy to try, but not sure what you had in mind.

But first, I need to settle on a solution to buy.


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## duffin (Jul 25, 2011)

Cool icycle! Can't wait to hear the results!


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## pastajet (May 26, 2006)

Accuracy aside, constant GPS usage sucks the iPhone dry, while the Garmin Edge series will keep crunching along.


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## NoahColorado (Aug 3, 2004)

I tested the Edge 200 vs. Motorola Droid X this past weekend. The phone was consistently faster on segments (usually 1-2 seconds, but one segment was 12 seconds). The phone also gave me an additional 1/10 mi. on a ~4 mi track. The trails I tested were pretty flowy without any tree coverage or massive elevation changes - I suspect those two things further amplify the discrepancies.

Strava racing has gotten pretty heated amongst my friends lately and I had suspected their times were not legit on some sections - they use phones and I use the Edge 200.


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## RaveOn (Dec 21, 2003)

I've found the GPS in the iPhone to be accurate in open and straight runs. The tight technical twisty trails I ride it way off. It doesn't refresh fast enough so when you do a quick 180 around a tree, it generally misses that.

I only use my 4s for basic mapping. For accuracy. I'd stick with a dedicated unit.


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## Harold (Dec 23, 2003)

read this thread, particularly icycle's posts about his discussions with app developers about phone GPS.

http://forums.mtbr.com/gps-hrm-bike...ht-iphone-gps-add-vs-new-handheld-771627.html

the quality of track that comes from a phone is very app- and settings- dependent. there are SO MANY variables that it's going to be really hard to show real numbers.

what would be useful in such a comparison would be an app that takes raw data from the phone GPS and records it without its own processing algorithms. that could give us a baseline from which we can compare apps, make comparisons between phone models, and finally compare dedicated gps receivers to different phones and different apps.


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## ghettocruiser (Jun 21, 2008)

The op's post is almost a month old now, but since I've been monkeying with Strava a lot this spring I'll say that a garmin edge, set to log every second, with the ANT+ wheel sensor has got to be the best way to do it. If you're going to bust yer ass trying to place on a 5-minute a climb that is timed to the second, being ripped off 2 seconds by your phone is a harsh result.

My phone GPS acquires my location much faster than the edge, but it's ongoing speed accuracy is always worse than with the garmin, even when not using a wheel magnet.


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## NoahColorado (Aug 3, 2004)

I've concluded my little experiment and deleted the second Strava account I had for checking phone (Droid X) vs. GPS. In all but one segment (today actually), the phone was consistently faster by anywhere from 1-18 secs on several segments lasting 5-12 mins. Today I checked both against a laptimer on both downhill and uphill segments where I knew the start and finish pretty well.

Climb
Phone 10:27
GPS 10:28
Laptimer 10:35

Downhill
Phone 5:42
GPS 5:41
Laptimer 5:46


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## Slozomby (Mar 22, 2012)

pastajet said:


> Accuracy aside, constant GPS usage sucks the iPhone dry, while the Garmin Edge series will keep crunching along.


if cell reception is spotty in the area your phone will run dry quick .and lets face it when in woody hilly area cell reception is spotty at best. and there doesnt tend to be great views of the sky. i've logged 6 hours straight on the phone in airplane mode. motionX + mp3's + bluetooth headphones with the screen fairly dim. i'm more than content to not be able to surf the web or get phone calls while riding.

i wouldn't want to call in a precision bombing run from an iphone fix. but for general navigation , ie. there's a fork coming up and i need to turn left, its just fine. its not like your riding by instrument.


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## asphalt_jesus (Aug 13, 2010)

pastajet said:


> Accuracy aside, constant GPS usage sucks the iPhone dry, while the Garmin Edge series will keep crunching along.


#1 Put your iphone in 'airplane mode' quite a bit of what's sucking the battery dry is hunting/staying in touch with a cell tower.

#2 How much the GPS app uses depends on how much time the developer spent optimizing their code for battery time.

I don't understand the need for such precision while riding a bike. Someone please explain it to me.


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## Harold (Dec 23, 2003)

asphalt_jesus said:


> #1 Put your iphone in 'airplane mode' quite a bit of what's sucking the battery dry is hunting/staying in touch with a cell tower.
> 
> #2 How much the GPS app uses depends on how much time the developer spent optimizing their code for battery time.
> 
> I don't understand the need for such precision while riding a bike. Someone please explain it to me.


I think you've got your terminology mixed up.

precision - the number of decimal places reported in a measurement, did you ride 10.0mi or 10.000mi?

accuracy - repeatability of a series of measurements, or, the spread of variation between measurements. are we talking +/- 2.0mi or +/- 0.2mi over the course of a 10mi ride?

I am concerned, as a user, with the accuracy of my measurements. if I go out and ride the same section of trail 10 times, I want all 10 measurements to be very close to each other. it doesn't matter much to me how close those measurements are to someone else's chosen recording device. as a guy who volunteers for trails, I am concerned not just with reported metrics like distance, but I am actually concerned with the positional accuracy - how close to the actual on-the-ground trail does my GPS report my position?

precision has come up as increasingly important as folks use their recorded rides to compete with each other. First, folks just compared numbers on their cyclocomputer. with the expanding use of GPS and the creation of sites like Motionbased years ago, folks could compare on the internet by sharing their GPS tracks. then Garmin released fitness GPS receivers and introduced the courses feature where you could virtually compete against those other people via their GPS tracks while you were on the trail. now there's Strava that's taken it a step further and we can compete on various trail segments like climbs and such. with the expansion of the variety of hardware used for these purposes, from fitness watches to handhelds to cycling GPS to phones, it's now becoming important to people's competitions that the devices have comparable levels of precision because these competitions come down to fractions of a second.


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## asphalt_jesus (Aug 13, 2010)

NateHawk said:


> ...., it's now becoming important to people's competitions that the devices have comparable levels of precision because these competitions come down to fractions of a second.


And that's where you lost me. People are obsessing about fractions of a second on their $4000+ bikes and need something more precise than an iPhone for temporary bragging rights. Wow.

No wonder beginners have such a hard time penetrating this sport.


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## Harold (Dec 23, 2003)

asphalt_jesus said:


> And that's where you lost me. People are obsessing about fractions of a second on their $4000+ bikes and need something more precise than an iPhone for temporary bragging rights. Wow.
> 
> No wonder beginners have such a hard time penetrating this sport.


what does that have anything to do with beginners?

some people really are that competitive.

I am not, I really don't care about fractions of a second. most people I know don't. but some do. who cares if they do or not?


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