GPX & FIT Files - Original vs Edited

Discussion related to the Garmin GPSMAP 67 series GPSr
User avatar
Matt16598
Posts: 14
Joined: Mon May 29, 2023 5:07 pm
Location: Oregon, USA

GPX & FIT Files - Original vs Edited

Unread post by Matt16598 »

*** Moved Here From Another Post That Had Gone Off Topic ***

Just now, I was able to export a track as GPX on my 66sr. However, the resulting data has much lower apparent accuracy. For example, Lat/Lon in the GPX from BaseCamp have 15 digits to the right of the decimal point; 66sr export has 10. Elevation from BaseCamp has 15 digits, and 66sr export has 2. At least the additional elevation precision from BaseCamp is probably meaningless, though; all of the values are essentially zero after the hundredths place, +/- some noise, so I think this is some kind of conversion error. I would be happy to post one or more of these GPXes from the unit, or the original FIT files, in case anyone is curious, but I really doubt it makes any meaningful difference for the comparison I was trying to do. :)
MarkHL
Posts: 33
Joined: Tue Feb 18, 2020 11:53 pm

Re: GPX & FIT Files - Original vs Edited

Unread post by MarkHL »

The GPX data file that is exported from a Garmin Fit data file in Garmin Connect is identical to the GPX data file saved on the 67 in addition to the FIT file.
User avatar
GPSrChive
Site Admin
Posts: 3883
Joined: Fri Jan 20, 2017 11:29 pm

Re: GPX & FIT Files - Original vs Edited

Unread post by GPSrChive »

Matt16598 wrote: Wed May 31, 2023 12:02 am Just now, I was able to export a track as GPX on my 66sr. However, the resulting data has much lower apparent accuracy. For example, Lat/Lon in the GPX from BaseCamp have 15 digits to the right of the decimal point; 66sr export has 10. Elevation from BaseCamp has 15 digits, and 66sr export has 2.
Since BaseCamp did not record the actual track data, and the GPSMAP 66sr did, how can BaseCamp be more precise? It can not. This is why I always like to have the raw GPX files copied directly from the device, untouched by any software, when performing any meaningful testing.

I am not suggesting that it always makes a difference, or even frequently makes a difference, but allowing any software to touch/manipulate the raw data always dilutes any test results provided.

I always keep an 'untouched' archive of all important device data that is copied manually from each device to my PC. These files can be loaded over and over into any number of third party software for future inspection and testing without ever changing a single byte of information in the source material.
User avatar
GPSrChive
Site Admin
Posts: 3883
Joined: Fri Jan 20, 2017 11:29 pm

Re: GPX & FIT Files - Original vs Edited

Unread post by GPSrChive »

MarkHL wrote: Wed May 31, 2023 12:42 am The GPX data file that is exported from a Garmin Fit data file in Garmin Connect is identical to the GPX data file saved on the 67 in addition to the FIT file.
They most certainly are not.
jlg2
Posts: 11
Joined: Tue May 30, 2023 2:50 pm

GPX & FIT Files - Original vs Edited

Unread post by jlg2 »

Before diving into the weeds, does the claim that the tracks were edited mean that translating from .fit to .gpx is "editing"? If so, I think that's nonsense.

Check my arithmetic. I believe latitude of nine digits of precision and longitude of nine digits of precision will specify an Earth-surface position with error of less than 2mm. In other words, the distance between H###.######,H###.#####0° and H###.######,H###.#####1° is always less than 2mm. At the poles, that distance would be zero. Please check my math. I'm not an expert. If I'm right, that's way beyond the accuracy of the devices in question. And I think both the .fit and .gpx formats are each capable of storing more than nine decimal digits. So in terms of error, the format doesn't matter.

As for the difference, the .gpx format is a text format. You can open a .gpx file and read it with a text editor like Notepad or Word. A .fit file is compressed into binary format. A text editor would display it as gibberish. So the same information needs more storage to be stored in .gpx format. I would hope that any translation algorithm would be invertible after the first pass. If it weren't then translating back and forth between .fit and .gpx several times might lose precision, but I don't see how even that hypothetical loss would be relevant here.

Some Garmin documentation says positions stored in .fit are slightly more precise than the same position stored in .gpx. I've asked around some but never gotten a coherent answer to exactly what that means or how that's even possible.
Last edited by jlg2 on Wed May 31, 2023 2:49 am, edited 3 times in total.
mimichris
Posts: 435
Joined: Sun Jan 13, 2019 7:59 am

Re: GPX & FIT Files - Original vs Edited

Unread post by mimichris »

What is unfortunate is that the Garmin GPX does not display the type of GPS in the data, it would be nice to do so.
My GPS Cross Twonav displays it, as well as its serial number.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
Przekątny
Posts: 125
Joined: Fri Apr 07, 2023 9:30 pm

Re: GPX & FIT Files - Original vs Edited

Unread post by Przekątny »

mimichris wrote: Wed May 31, 2023 7:05 am What is unfortunate is that the Garmin GPX does not display the type of GPS in the data, it would be nice to do so.
I cannot agree with this sentence, the gpx file contains information about the software in which the file was created.
Check in your gpx files.
mimichris
Posts: 435
Joined: Sun Jan 13, 2019 7:59 am

Re: GPX & FIT Files - Original vs Edited

Unread post by mimichris »

Przekątny wrote: Wed May 31, 2023 10:23 am
mimichris wrote: Wed May 31, 2023 7:05 am What is unfortunate is that the Garmin GPX does not display the type of GPS in the data, it would be nice to do so.
I cannot agree with this sentence, the gpx file contains information about the software in which the file was created.
Check in your gpx files.
I expressed myself badly, I am not talking about the software but about the type of GPS, for example the GPSMAP67 and its serial number. I did not find in the original Garmin files in GPX.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
Przekątny
Posts: 125
Joined: Fri Apr 07, 2023 9:30 pm

Re: GPX & FIT Files - Original vs Edited

Unread post by Przekątny »

mimichris wrote: Wed May 31, 2023 10:54 am I expressed myself badly, I am not talking about the software but about the type of GPS, for example the GPSMAP67 and its serial number. I did not find in the original Garmin files in GPX.
Maybe I expressed myself wrong, the device has software that saves the device name in the file, Garmine device number is not saved in the gpx file, only the device name is saved.
JungleJim
Posts: 253
Joined: Sat Mar 05, 2022 3:45 pm
Location: Netherlands

Re: GPX & FIT Files - Original vs Edited

Unread post by JungleJim »

The FIT file format is much better in that regard, it includes info on the device that captured the data, see screenshot.
A GPX file recorded on the GPSMAP 67 only includes the name of the device (GPSMAP 67), and that in a field that is not really meant identifying detailed info on the device being used.
FIT file device info
Schermafbeelding 2023-05-31 125835.png
You do not have the required permissions to view the files attached to this post.
Current: GPSMAP 67, Edge 1040, inReach Messenger - Previous: GPSMAP 66sr, Oregon 700, Dakota 20, Edge 1030 Plus, Edge 1030, Edge 520 Plus, Edge 520
Post Reply

Return to “GPSMAP 67”