Track Distance Discrepancy between Summary and Graph

I'm puzzled by the discrepancy between the Total Distance shown in Basecamp when I have downloaded a track from my Garmin Montana 600. The summary section under the Properties tab indicates the walk distance was 23.0 km but when I go to the Graph tab to see elevation, the total walk comes up as 18.5 km. Incidentally, both the track and trip distances on the GPS indicated 23.0 km also. But which is correct?

Here are the screen shots from Basecamp:

Here is the Track from the GPS:

I really would like to know my exact distance walked and amount of ascent. Thanks.

0 BTLAAKE over 10 years ago

I’m puzzled by several things.

First off, I’m still using BaseCamp version 4.2.5 and when I load the gpx file I get different values for Ascent (1332 m vs. your 1396m) and Descent (1350m vs. your 1414m).

I don’t know if you noticed it or not, but we both get an Elapsed Time of 1 DAY and 5+ hours versus the 11+ hours indicated in the table and the gpx file.

The numbers (except for area and grade) that you are seeing in the BaseCamp Track Properties window come from a header for the track in the gpx file (the gpxtrkx extension for the Garmin folks). I assume the gpx file was created on Montana 600, but I do not know the source of the values. The values could be from the trip computer (was it reset?).

In any event, the actual track data gives a distance of 18.544 km. The total ascent in the gpx file is 1953.56m (total descent is 1970.86m) by my calculation (sums of all positive changes in elevation and all negative changes in elevation).

You can force a recalculation of the Summary data by deleting a single point (one with a small leg distance and slow speed – say point 7 in your data) by clicking on one in the table, pressing delete and clicking in the Summary area above the table. After seeing the changes, use ctrl-z or edit>undo to restore the data.

I’m still puzzled by the Ascent/Descent data that I see in v4.2.5 as it is still off after deleting a single point to force a recalculation. I wonder if you see the same thing when deleting a point from the table.

I also don’t know where the extra 17 some hours are coming from for the elapsed time and if it is related to the total distance error.

0 jm47048 over 10 years ago

To the OP, I will try and recreate your issue. Thank you for posting the file.

To BTLAAKE, can you post some data for me to look at as the OP did?

0 AnnieMacD over 10 years ago

Thanks both for your replies.

@BTLAAKE. I did not know about deleting a point and then recalculating. When I did as you suggested, I then got the distance to be 18.5km and the ascent/descent as you did. Also the total time (which I did notice but forgot to mention in my original post) calculated correctly AND it totally changed the ratio of time moving to amount stopped. (Original was moving - 9:23:42, stopped - 1:56:38 for total 1 day 5:19:49. New is moving - 6:30:06, stopped - 4:49:37 for total 11:19:43) I do think the moving/stopped on the recalculation to be more accurate as I was watching a mountain marathon for much of the time and taking lots of photos and I found it unbelievable that I was only stopped for under two hours.

@JM47048. Thanks for trying to help me. I have just had a bit of an "Ah, ha" moment as all this started to go awry when I changed the way I start off on my walks. On the Montana 600, I used to reset the trip data and then go to the track, delete the Current Track and then Start Tracking. Then my track data and trip data were always different. I now suspect the track data was correct and the trip data wrong. Recently, I just went in to the Trip and rest both Trip and Track Data and start Tracking. Now they are always the same but, I suspect, wrong. (Hope all this makes sense.) Wonder if this is the crux of the issue and if all I have to do is go back to my original process, that's fine. But wonder why the trip data is inaccurate (although I realize it's not your problem).

0 jm47048 over 10 years ago

Glad we got a little further on your issue. Like I said, I will try to get to recreating your issue shortly, hopefully tomorrow morning.

0 AnnieMacD over 10 years ago

Well, I went on another hike yesterday and used my 'old' routine of clearing the trip data on it's own and clear track separately and then Start Tracking. Unfortunately I had similar results as before. Both track and trip showed the same results:
Ascent - 929m
Moving Time - 5:08
Stopped Time - 1:20
Distance - 13.65 km

I saved the track and opened it in Basecamp. Same figures as above. I then deleted one point and re-calculated to get the following:
Ascent - 903m
Moving - 4:19
Stopped - 2:09
Distance - 11.7 km.

I'm now wondering if this started happening when I got the firmware update from Garmin?? I can't remember when this was and it may have nothing to do with it.

The thing that's really worrying me (for such an expensive unit) is that I have no faith in the results showing on my GPS.

Thanks for any insight you can provide.

0 BTLAAKE over 10 years ago

I suspect it was due to a recent firmware update. I just checked my 62 device and see similar things happening. If it really bothers you, do a search for a wiki page for your Garmin Montana model. The wiki pages will sometimes keep most of the firmware versions with instructions on how to revert back to an earlier version. Use at your own risk.

As far as insight goes, I’ll do my best, but remember that some of what follows is speculation. The short version is that it appears that Garmin has decided to append data from the trip computer to the beginning of the track log. When you look at the summary data for a track on your device you are seeing this appended data and not results calculated from the actual logged data. When the track is downloaded to the BaseCamp and the Track Properties window is opened, it is grabbing the appended data in the track log (i.e. the values displayed by the trip computer) for the summary statistics. However, track logs only store position (Lat/Lon/Elevation) and UTC time for each point. So, BaseCamp must calculate most of the data in the table below based on the saved data points. When the graph is pulled up, it is based on the calculated results (thus the initial difference between the graph distance and the summary table distance). When a point is deleted from the table, BaseCamp will recalculate the data table AND the summary statistics.

The Trip Computer on the device and real time data fields likely update with every returned position solution (every 1 second). So, the trip computer summary data for your recent 6:28 track is based on ~23,280 points. Even if the distance field is updated only when the device thinks it is moving, it would still be based on ~18,480 points. The track log will contain far fewer points. Devices do not give our true position. Imagine walking an absolute straight line. The recorded track will not be straight, but have small deviations to the left and right. The more points collected, the larger the accumulated error. That is why the trip computer is giving a longer distance than the actual track.

Moving/stopped time and ascent/descent are a bit more complicated.

0 jm47048 over 10 years ago

I suspect it was due to a recent firmware update. I just checked my 62 device and see similar things happening. If it really bothers you, do a search for a wiki page for your Garmin Montana model. The wiki pages will sometimes keep most of the firmware versions with instructions on how to revert back to an earlier version. Use at your own risk.

As far as insight goes, I’ll do my best, but remember that some of what follows is speculation. The short version is that it appears that Garmin has decided to append data from the trip computer to the beginning of the track log. When you look at the summary data for a track on your device you are seeing this appended data and not results calculated from the actual logged data. When the track is downloaded to the BaseCamp and the Track Properties window is opened, it is grabbing the appended data in the track log (i.e. the values displayed by the trip computer) for the summary statistics. However, track logs only store position (Lat/Lon/Elevation) and UTC time for each point. So, BaseCamp must calculate most of the data in the table below based on the saved data points. When the graph is pulled up, it is based on the calculated results (thus the initial difference between the graph distance and the summary table distance). When a point is deleted from the table, BaseCamp will recalculate the data table AND the summary statistics.

The Trip Computer on the device and real time data fields likely update with every returned position solution (every 1 second). So, the trip computer summary data for your recent 6:28 track is based on ~23,280 points. Even if the distance field is updated only when the device thinks it is moving, it would still be based on ~18,480 points. The track log will contain far fewer points. Devices do not give our true position. Imagine walking an absolute straight line. The recorded track will not be straight, but have small deviations to the left and right. The more points collected, the larger the accumulated error. That is why the trip computer is giving a longer distance than the actual track.

Moving/stopped time and ascent/descent are a bit more complicated.

Have you tried to recreate this in 4.3.4?

0 jm47048 over 10 years ago

to the OP, I have opened a case for your issue.

0 BTLAAKE over 10 years ago

Have you tried to recreate this in 4.3.4?

No, still running Windows XP. Will gladly accept a laptop with newer operating system and a Montana for testing. The OP provided a gpx file you can use - its the same file I looked at in 4.2.5. I assume you got the data I sent you.

The addition of adding gpxtrx extension data (GpxExtensions V3) at the beginning of a track on the 62 is fairly recent. The error in total distance indicates the data comes from Trip Computer. As far as I know, the Trip Computer on the device updates every second. More data points will result in longer total distance.

In my version of BaseCamp (4.2.5) the Track is read in without any recalculation. The changes to stopped/moving time after recalculation (deleting a point) indicates that BaseCamp is trying to redetermine these values based on some simple logic (say threshold of speed between points). Changes are likely to occur due to the many options for data logging and will be most problematic for activities at slower speeds (slow walking) with less frequent data logging (a 20 sec log interval might consist of 12 sec stopped and 8 sec moving but will be all stopped or all moving in the recalculation).

0 AnnieMacD over 10 years ago

Thanks, both, for trying to explain and solve my problem. Two additional pieces of information. This started happening in April 2014, specifically between 4/12 and 4/18. At the same time the sum of moving time plus stopped went awry. Additionally, I notice that the status line at the bottom of the screen in Basecamp always shows the correct information, ie. matching the graph distance and the time is correct.

And, I'm a slow walker and stop frequently as I take lots of photographs. But you can see my stop/start from the track I sent!

Thanks to you both for trying to get to the bottom of this.