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Help please - GPS riddle

Magwood

Veteran Member
Camino(s) past & future
See signature line for links to daily posts to blogs from many caminos
I have been using the app 'mapmywalk' on my iPhone 5 to track my local walks and camino stages. I like the app but it doesn't seem very user friendly when it comes to sharing tracks. I was advised that 'wikiloc' would produce the files that I want to share, and so I also downloaded this app to my phone.

Today I used both apps at the same time, switched them on within seconds of eachother and set off for a walk. I am now rather puzzled that each app shows a different result for the distance walked
- mapmywalk - 9.7 km
- wikiloc - 8.9 km

Quite a significant difference. How can this be?

Many thanks for any help with this brain teaser.
 

dougfitz

Veteran Member
Camino(s) past & future
Spain: Mar 2010, Apr 2014, May/Jun 2016. Norway/Sweden: 2012, 2018. Other: 2011, 2019. CP (tbc)
Welcome to the real world of GPS! There are any number of possible causes of this:
  • you have a device that has known issues as a GPS receiver. A search on 'iphone 5 gps accuracy issues' gets over 3 million results.
  • even if there weren't issues with the device, not every GPS receiver delivers the same accuracy. See this site for a comparison of watches. Even those from the same maker show quite marked differences in accuracy.
  • GPS apps collect a series of points, and calculate the distances between them. There are two issues here:
    • there is inherent inaccuracy in the location of any particular point; and
    • the mathematical calculation may also have inaccuracies, such as rounding errors.
  • you are using two different apps, which may not be using the same points for their individual calculations. They may be sampling at different times or different frequencies. This will lead to differences between the distances they calculate.
So is the difference really that big? I know you think it is, but I rather suspect its not as bad as you think. The best estimate for the distance you travelled based on your post is 9.3 km, in which case the readings would be out by 400m (that's the joy of averages!). That's an error of less than 5%, and perhaps tolerable in the circumstances.

Edit: here is another really good resource that explains your problem: http://cincyhalfmarathon.com/GPS Accuracy.pdf.
Edit2: as a comparison, a search on 'garmin gps accuracy issues' gets about 25o,ooo results, Tomtom a few thousand more.
 
Last edited:

Magwood

Veteran Member
Camino(s) past & future
See signature line for links to daily posts to blogs from many caminos
Thank you so much @dougfitz for taking the time to explain this to me.

I guess I had an expectation that the readings from the two apps would be exactly the same, so the difference did seem major.

So, do you think that if I took the average distance from these two apps, it is likely to be accurate(ish)?
Or is that too much to hope for?

I will be setting off on the camino Mozárabe from Málaga in a few weeks and was hoping to share my stage routes with anyone who is interested. Over 1,200 km 5% would be 60 km - 2-3 days' walking. But as I don't want to carry any more technology I guess inaccurate will have to do.

Do you have a favourite app for measuring distance?

Again, thank you
 

CaptBuddy

Active Member
Camino(s) past & future
Fall 2012, again Fall 2014.
Magwood, I hate to add to the mix, but....

I use Pathaway Lite ($5) on my iphone 4s. It works very well and has an easy Export to GPX or KML file.
I also used it on an Android phone before the iphone.
The Pathaway app does have several feature that I do not use, nor have investigated. But for tracking my walks, it is very good.
There are 2 additional "Pro" versions, but I have read reviews that say don't bother.
 

dougfitz

Veteran Member
Camino(s) past & future
Spain: Mar 2010, Apr 2014, May/Jun 2016. Norway/Sweden: 2012, 2018. Other: 2011, 2019. CP (tbc)
So, do you think that if I took the average distance from these two apps, it is likely to be accurate(ish)?
Or is that too much to hope for?
Its the best you have, but as I pointed out, any single measurement has known inaccuracies. If you want an accurate assessment of which is the more accurate app, find a local sports ground that has a 400m track. Do 4 or 5 km (10 or 12.5 laps) using your GPS sticking to the inside lane, and compare the results. You could shorten the distance if you feel you will be bored or lose count, but the more you can do the more realistic will be the result.

Other members of one of the walking clubs I belong to do this test from time to time, and are surprised by the differences between their known and quite accurate distance and the distance their GPS watch has measured. I then have fun explaining to them that they would get a more accurate distance measurement using an old fashioned measuring wheel or by calibrating their bicycle.

I will be setting off on the camino Mozárabe from Málaga in a few weeks and was hoping to share my stage routes with anyone who is interested. Over 1,200 km 5% would be 60 km - 2-3 days' walking. But as I don't want to carry any more technology I guess inaccurate will have to do.
The distance you have to walk won't change - its just the accuracy of the measurement, and perhaps your perception based on that about how much you have done. If you can share the track, your friends won't know if there are minor inaccuracies along the way, and those who might use the track will appreciate the information anyway.

Do you have a favourite app for measuring distance?
I use a Garmin eTrex 30 and either the older Mapsource or newer Basemap applications. I have tried some smartphone apps such as mapmywalk, but wasn't particularly impressed. On my phone, the GPS is a battery hog. I sometimes carry a tablet that has a GPS that doesn't appear to drain the battery quite so much, but I haven't used that for serious walking.
 

KinkyOne

Veteran Member
Camino(s) past & future
I'am not perfect, but I'm always myself!!!
If you want an accurate assessment of which is the more accurate app, find a local sports ground that has a 400m track. Do 4 or 5 km (10 or 12.5 laps) using your GPS sticking to the inside lane, and compare the results.
Thank you, Doug. I'll take your advice with my Endomondo app (Android) before departure to Levante this June. Last year my GPS tracks were almost everyday longer than distances in guidebooks :)
 

C clearly

Moderator
Staff member
Camino(s) past & future
Frances (2012, 2014, 2015, 2016), VDLP (2017), Mozarabe (2018), Vasco/Bayona (2019)
Good explanations! I haven't used these apps because of the battery issues, although I'm always thinking I'd like to.
 

newfydog

Veteran Member
Camino(s) past & future
Pamplona-Santiago, Le Puy- Santiago, Prague- LePuy, Menton- Toulouse, Menton- Rome, Canterbury- Lausanne, Chemin Stevenson, Voie de Vezelay
I bought the monster iPhone 6 plus just for travel. It is big enough to leave the ipad behind. Another upside is the battery power----the GPS really does not eat up that much on it compared to the iPhone 5.
 

wayfarer

Moderator
Staff member
Camino(s) past & future
SJPP-Santiago-Finistera-Muxia. April/May 2012
Sarria-Santiago Sept. 2013
SJPP - Almost Orrison April 2014
@Magwood, I use the "My Tracks" app for walking on my Samsung S5 and I believe there is a version for IOS. I find it very accurate and is light on the battery. I used it a few months ago on a six hour hike and there was no discernible loss on the battery above the normal. It is a simple app to use, I found a few of the others a bit more complicated and aimed at serious training and biking, but most people have their own preferences.
Thanks to @dougfitz I looked up the GPS accuracy for the Samsung S5 online and found the top four reviews on Google to be positive. Thank you Doug.
 

newfydog

Veteran Member
Camino(s) past & future
Pamplona-Santiago, Le Puy- Santiago, Prague- LePuy, Menton- Toulouse, Menton- Rome, Canterbury- Lausanne, Chemin Stevenson, Voie de Vezelay
Here's a blow up of a part of hike recorded on three different gps units---a Garmin, a Samsung and an iPhone. We were looking at rocks so we weren't on a set trail, but you can see they all have some wander, and all are accurate to the width of a couple of big Ponderosa pines.

gpss.JPG
 

KinkyOne

Veteran Member
Camino(s) past & future
I'am not perfect, but I'm always myself!!!
Absolutely agree. I don't think I could get 6 or 8 hours out of mine. Maybe 4 hours at most.
I'm using GPS app only for tracking my way and I put my phone in airplane mode during walking. The battery lasts for whole day with no problem. It even allows me to make additional photos and possible texting.
 

kmrice

Active Member
Camino(s) past & future
Santiago - Fisterra 2008
St. Jean Pied de Port - Santiago 2013
My father used to say that a man with a watch knows what time it is; a man with two is never sure.

I use MotionGPS on my iPhone; whatever it says I did, that's my story and I'm sticking to it.

Karl
 

grayland

Moderator
Staff member
Camino(s) past & future
Yes
I use MapMyWalk for walking and training at home.
I have found the MotionGPS is much better for use in Spain. You can preload base maps of the area in Spain you are walking and have a very good local map when needed.
Newfydog has posted some very good threads on using GPS in Spain. I use an iPhone with no problems. I do take a "juicer" or portable battery to use if the phone battery gets low. It is often easier and safer to recharge the juicer than the phone itself when you are in a public place and can't stay with the phone all the time. The juicer is much less of a theft target than a phone.
 

Magwood

Veteran Member
Camino(s) past & future
See signature line for links to daily posts to blogs from many caminos
@Magwood, I use the "My Tracks" app for walking.
Thanks @wayfarer i shall take a look.

I do take a "juicer" or portable battery to use if the phone battery gets low. It is often easier and safer to recharge the juicer than the phone itself when you are in a public place and can't stay with the phone all the time. The juicer is much less of a theft target than a phone.
Yes, I took a external charger last year and found it very useful, for the reasons stated. It will come again on this camino.

Thanks to all who have contributed to this thread. I am sure many people will find it interesting (and many more will be gnashing their teeth wondering why we desire our toys).

I will try a variety of apps over the next few weeks and see what combination seems to agree with eachother. But as you so rightly say @dougfitz the distance I walk will not be altered by what the app says.
 

peregrina2000

Moderator
Staff member
Thank you, Doug. I'll take your advice with my Endomondo app (Android) before departure to Levante this June. Last year my GPS tracks were almost everyday longer than distances in guidebooks :)
I absolutely do NOT want you to tell me that your distances were wrong, because I was so encouraged when your device told me I actually walked 43 km on the Invierno when I had thought I was walking 37! So let's just leave those distances the way they are. :)
 

KinkyOne

Veteran Member
Camino(s) past & future
I'am not perfect, but I'm always myself!!!
I absolutely do NOT want you to tell me that your distances were wrong, because I was so encouraged when your device told me I actually walked 43 km on the Invierno when I had thought I was walking 37! So let's just leave those distances the way they are. :)
:D:D:D:D:D
OK, Laurie ;)
 

dougfitz

Veteran Member
Camino(s) past & future
Spain: Mar 2010, Apr 2014, May/Jun 2016. Norway/Sweden: 2012, 2018. Other: 2011, 2019. CP (tbc)
I absolutely do NOT want you to tell me that your distances were wrong, because I was so encouraged when your device told me I actually walked 43 km on the Invierno when I had thought I was walking 37! So let's just leave those distances the way they are. :)
Well, walking with a GPS never changed the distance, only our perceptions!!
 

Magwood

Veteran Member
Camino(s) past & future
See signature line for links to daily posts to blogs from many caminos
I guess an apology might be due to Mr Brierly. I berrated him several times in my blog from the camino portuguese for stating the wrong stage distances. Maybe he was just using a different measuring device!

Sorry Mr B!
 

KinkyOne

Veteran Member
Camino(s) past & future
I'am not perfect, but I'm always myself!!!
I guess an apology might be due to Mr Brierly. I berrated him several times in my blog from the camino portuguese for stating the wrong stage distances. Maybe he was just using a different measuring device!

Sorry Mr B!
I've found Brierley's distances (2011 edition of CF guidebook) the closest to distances recorded with Endomondo. Of course last year I walked only from Sahagun to Ponferrada. Guides for C.de Madrid and C.de Invierno had much bigger discrepancies than Brierley. I could comment on that also but that would already be off-topic :)
 

MichaelSG

Retired member
Camino(s) past & future
Not enough
I guess an apology might be due to Mr Brierly. I berrated him several times in my blog from the camino portuguese for stating the wrong stage distances. Maybe he was just using a different measuring device!

Sorry Mr B!
You can still berate him for giving the "as the crow flies" km's more prominence than the "as the pilgrim walks" distances.

On a related note though, I'm looking for a good GPS app that will allow me to import gpx files easily and view them on a map, preferable the Google or iPhone map that I already have. On the Camino Ignaciano, the website gives great gpx files for the whole route so I don't need to create new files or measure how far I've gone but it would be nice to look at a map occasionally and see if I am still on course. Does anyone have a suggestion?
 

kmrice

Active Member
Camino(s) past & future
Santiago - Fisterra 2008
St. Jean Pied de Port - Santiago 2013
I'm looking for a good GPS app that will allow me to import gpx files easily and view them on a map, preferable the Google or iPhone map that I already have
Motion-X GPS. You can import gps files and you can download the maps you want (as Google Maps or, in my opinion, even better, MotionX Road or MotionX Terrain, or many others) in advance. After that you need no cell data to use the app and see where you are on the maps.
 

newfydog

Veteran Member
Camino(s) past & future
Pamplona-Santiago, Le Puy- Santiago, Prague- LePuy, Menton- Toulouse, Menton- Rome, Canterbury- Lausanne, Chemin Stevenson, Voie de Vezelay
One hint for getting accurate GPS distances----turn it off when you stop for lunch, particularly if you go inside. If you don't the GPS will continue to recalculate the position, perhaps in error if it has a poor signal, and every new position is added to the distance. A long lunch can add a kilometer, without going anywhere!

gpserror.JPG
 

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