Question about GPS distance calculation

[Wlzzz]

I'm not sure if this is the right place to ask, but this question is more directed to the developers.

So I'm interested that how the distance is currently calculated from the GPS data. I ask this because I'm seeing wrong distance calculated from data that seems to be just fine.

Here is my scenario:

I went to ski and started hike activity with connected GPS from my Charge 2.

I know that the route which I traveled is about 7km long.

At the end of the route I stopped the activity and it shows that I have traveled 4km distance. So 3km are missing.

I went home and checked the GPS data from map and it seemed just fine. No huge gaps or anything in the data.

Next I downloaded the TCX file from that exercise which contains the GPS data in xml format.

The TCX file seems to contain each GPS coordinate it takes during the exercise. Also there seems to be the distance in each trackpoint element. In the end of the file the distance is this incorrect 4km.

So next I wanted to do little test that what kind of distance I get if I use that GPS latitude and longitude data and calculate the distance myself.

So I wrote little python script which parsed each latitude and longitude element from that file. Then I used haversine formula  to calculate distance between two GPS coordinates. So my script iterates all GPS longitude and latitude points and calculates the distance between them and adds them together in one variable.

And what result did I get from this experiment? 7km.

So now I'm really curious that where this distance variable in that TCX file comes from? Is it calculated by the Fitbit App or does this come from phones GPS service?

[LanuzaFitbit]

Hello @Wlzzz! 

Thanks for bringing that up. There is currently an issue with the app in which the incorrect distance is showing for GPS tracked activities like Hike or Walk. As a workaround, some users have had a better experience using the 'Run' option as it seems that, for some reason, it is being more accurate. I'd recommend giving it a shot. Please keep in mind that it might show incorrect distance too as not everyone has reported it to work.

The distance comes from the mobile device's GPS data, to answer your question.

Please let me know if there is anything else I can help you with.

[Wlzzz]

Thanks for your response. I still have some followup questions.

Well it seems weird that 'Run' option is more accurate. What does it do differently in your app related to GPS?

And the reason why I use hike while skiing is because hiking is the only type of GPS supported exercise I don't normally do. Using 'Run' would mix the results with my actual runs. This would not be a problem if I could change the exercise type later from the App, but it wont allow me to do it because you can only edit GPS tracked activity to another activity which supports GPS. I can't understand why it is limited this way in the first place.

Just to be clear, does the distance come directly from the geolocation API which Fitbit App uses, or is there distance calculation inside Fitbit App with the GPS coordinates provided by the API? Either way, I was able to use that same GPS data and calculate the correct distance. So there has to be a bug in some end.

I still haven't tested how other Apps manage the GPS on my phone. Maybe next time I use another application alongside with the Fitbit one just to be clear if it is just Fitbit App which gets the distance wrong on my phone.

[LanuzaFitbit]

Hey @Wlzzz.

I understand where you are coming from. I wouldn't be able to tell you what is the exact process in which the distance is calculated, or taken, from the phone itself. I'd rather not make anything up. 

What I can tell you is that the situation is being looked into and that as soon as there are any updates I'll be sure to let you know.

Feel free to ask me any other questions and I'll be happy to reply so the best of my ability.

[CLIM]

I also experience the same using Versa connected GPS.  It total distance is less than actual.  I checked a few Trackpoints and calculated the distance using https://gps-coordinates.org/distance-between-coordinates.php.  It seems off.  Will this issue be addressed?  

[LanuzaFitbit]

Welcome to the Forums @CLIM.

Thanks for sharing that! 

Unfortunately we do not have any news on the situation. I'll keep trying to get any updates and a post about them as soon as I get anything.

Thanks for your patience and understanding.

Let me know if there is anything else that I can help you with.

[GaiusCoffey]

Hi,

I have the exact same issue - after accidentally selecting "Hike" rather than "Bike" (I wasn't wearing glasses) a tracked bike ride of approximately 50km was measured instead as a hike of 18.69km!

Again, all of the GPS points appear accurately, but the mapping of distance travelled is laughably incorrect - if I select in the app to show the KM markers, there is a variance where two adjacent markers at one stage of my route appear to be four or five times further apart than those elsewhere...

Running GPS appears accurate, cycling GPS appears accurate... so why is "Hike" (which I have now deleted as a shortcut from my Surge) so laughably, uselessly, ridiculously inaccurate?

And, more to the point, how can I go about getting my route recalculated using the accurate GPS points that were uploaded?

And, yes, I have contacted support about this, but apparently they do not have either the access or the technical know how to do anything useful - the only solution they have offered so far (deleting and relogging as a bike ride) would mean I lost the route and any valid stats.

G

[CLIM]

I believe nothing wrong about the GPS points.  I noticed that my watch periodically shows "connecting" when recording.  It is when the watch loses the GPS points and not able to get correct distance.  I have been emailing the Fitbit support since Sept.  If you just go straight, the distant would be correct as missing a few points in between does not matter.  It makes a huge difference if you are running or cycling on a trail.  At one point, Fitbit Support acknowledged the problem and told me the Dev team had been working very hard to fix it.  Few months until now, even with the latest version of Fitbit OS and latest version of App, the problem still persists.  I hard reset the watch and reinstalled the app a few times as the support team suggested, nothing helps.   Connected GPS simply does not work.

[GaiusCoffey]

No, the points are there. 

I could show you a spreadsheet I made from the TCX file collected by Fitbit - everything is correct apart from the distance and speed calculations. 

When I recalculated based on latitude & longitude, the distance more or less equalled Google maps - 54.5 rather than 18.69. 

I don’t know why this issue affects Hike but not Bike or Run, but that is a different discussion. 

So although any GPS can occasionally skip points, the issue here is specifically limited to calculating distance and speed in Hike. 

G

[ftomazi]

For me, this happens with bike, when i export to strava.

i take a look the tcx file and many point tha distance is the same, but coordenates gps is ok.

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@GaiusCoffey wrote:

No, the points are there. 

I could show you a spreadsheet I made from the TCX file collected by Fitbit - everything is correct apart from the distance and speed calculations. 

When I recalculated based on latitude & longitude, the distance more or less equalled Google maps - 54.5 rather than 18.69. 

I don’t know why this issue affects Hike but not Bike or Run, but that is a different discussion. 

So although any GPS can occasionally skip points, the issue here is specifically limited to calculating distance and speed in Hike. 

G

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[GaiusCoffey]

Because TCX file contains calculated distances, simply importing into a new app doesn’t correct Fitbit’s wrong calculations. 

You need to extract the latitude/longitude coords and recalculate. 

[LanuzaFitbit]

Hello @GaiusCoffey, @CLIM and @ftomazi.

Thanks for reaching back with all of those details. I apologize for the delay in my reply.

In this case I'd like to ask what Fitbit is it that you are using. That should definitely help in determining what is going on.

Look forward to your reply.

[GaiusCoffey]

Not sure I agree that it is helpful; the issue appears to be back-end processing of the GPS rather than the device collection of GPS.

However, mine is a Surge.

[ftomazi]

my is a Blaze..

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@LanuzaFitbit wrote:

Hello @GaiusCoffey, @CLIM and @ftomazi.

Thanks for reaching back with all of those details. I apologize for the delay in my reply.

In this case I'd like to ask what Fitbit is it that you are using. That should definitely help in determining what is going on.

Look forward to your reply.

---

[LanuzaFitbit]

Hello @ftomazi and @GaiusCoffey.

Thanks for letting me know.

We will be sharing this with the rest of the team so that it can be looked into. As soon as we have any details on the matter we will be sure to let everyone know.

Feel free to reach out with any further questions.

[WayneLocklear]

I am having EXACTLY the same issue with my iconic.  I went for a 7.5 mile hike this weekend.....fitbit calculated it to 4.8 miles.  I then downloaded the tcx file and uploaded it to gaiagps.com to compare how that app would calculated milage with the same data.....gaiagps showed exactly what maps as well as two other devices on the hike said....7.5 miles

I have screenshots as well as files......I contacted support but they all they want do talk about is manually calculating stride.  That doesn't answer the question on how the iconic with built-in gps...captured the points that an independant app confirms to be accurate, but the fitbit app and pace are all way different.

Please help me, I go on a very long hike in two weeks and I purchased the iconic, replacing my blaze, just for this feature.  An accurate avg pace is essential when hiking...and without it was a total waste of money.

[LanuzaFitbit]

Welcome to the Forums @WayneLocklear.

Thanks for bringing this up and sharing those details on the matter. 

In this case I'd like to ask you if you are using the Fitbit app or the web Dashboard to check on it.

Whichever of the two, please try to use the other and check on the other for that same activity and verify if the information shown for that activity is the correct one.

I look forward to your reply. Please keep me posted on how it goes.

[GaiusCoffey]

@LanuzaFitbitseriously;

READ THE POST BEFORE ISSUING SOME MEANINGLESS AUTOREPLY.

What @WayneLocklear describes, and in fact what all of us have described, has absolutely _nothing_ to do with whether or not it is the dashboard.

It is now a _verified_ fault that has been _accepted_ as such by Fitbit that certain settings on the Fitbit watches cause the GPS _interpretation_ to be bogus despite the GPS _data_ being valid and correct.

Therefore, before you reply next time, please ask yourself these questions;

1. Does what I am answering offer any new information?

2. Is what I am answering relevant?

3. Is what I am answering in any way useful?

In this case, the answer to all three questions is "no".

I am aware that you are operating to guidelines for moderators in the community, but fobbing people off with flannel like the above is a very, very potent reason for me getting fed-up with Fitbit community and Fitbit support.

[LanuzaFitbit]

Hello @GaiusCoffey.

Thanks for your feedback.

I'm afraid my intention was not that. My intention with my previous post was to gather more information in order to better understand what is happening.

1. If the information shows accurately on either of the ends it can help narrow down what is going on.
2. If the situation is narrowed down, then it leads us closer to what is happening and thus a possible solution.
3. While it is not immediately useful as it is not a solution, and it is helpful in understanding the situation.

I hope this clarifies my intentions with my previous post.

Let me know if there are any questions I can help you with.

[WayneLocklear]

I have used both the app and fitbit.com dashboard and both are reporting the same.  

Additional information.  I went for a hike yesterday....had both gaiagps app on my phone tracking as well as fitbit iconic.  In this case both registered the same.  I'm starting to wonder if vertical accent calculations are at all part or all of the issue.  The hike yesterday only had about 250 vertical change where the hike on Saturday had about 1000.

Still seems like a lot of difference for that to be the cause.  Please remember, the points that were captured by iconic saturday do calculate out to the correct milage when uploaded to a different app (gaiagps)....so I don't believe it's a situation where the app wasn't capturing points during the hike.

Thanks, please ask any questions you want if we can get to the bottom of this inconsistancy issue.

Wayne