Total ascent figures

Discussion related to the Garmin GPSMAP 66 series GPSr
Spiney
Posts: 10
Joined: Thu Apr 04, 2019 9:35 am

Re: Total ascent figures

Post by Spiney » Fri Jun 14, 2019 11:59 pm

I have just read BLTAAKE's comments about the difference between the Trip Computer on Garmin devices and the GPX Track Log at https://forums.garmin.com/apps-software ... n-basecamp
In the past, there has been a confusion about why the Trip Computer data differed from the downloaded track log. Garmin has made two changes to their devices to address this. One is they made the Trip Computer a little smarter. It no longer logs every position solution, but only those where it decides the device has changed locations. This improved the total distance travelled, particularly for those just meandering about. The second change was to include the Trip Computer summary data with the downloaded Trip Log data.

This second change means that you no longer see summary data based on the data in the track log, but that of the trip computer. So, the device and BaseCamp agree exactly; but in truth, this is not a good thing to do.

If you are seeing Trip Computer summary data in BaseCamp, you can force recalculation based on the logged track data by deleting a single point in the track or dividing the track and then rejoining the track fragments. The former removes one data point, the latter adds one data point. The added point is a duplicate of one of the original track points.
If you follow the advice given and simply delete a single track point in BaseCamp, the improvement in accuracy of the cumulative ascent is staggering. I tried this for the track from a recent bike/hike in Scotland:

Original GPX loaded into Basecamp - ascent 2622m (WAY TOO HIGH!)
Image

Same file with trackpoint 3 deleted to force a recalculation - ascent 1890m
Image

This new figure is much closer to what I was expecting based on the map and guidebook.

Presumably Garmin's second change noted above also applies to FIT files too? I took a look at the FIT file for the walk:

I could not import the original FIT file for this hike directly into BaseCamp, so I had to convert it to a GPX first using GPSVisualizer. The initial converted GPX file had no elevation data, so I converted the FIT file again but adding elevation data from the GPSV's best digital elevation model. I then imported this new GPX file into BaseCamp. The 1880m total ascent using GPSV elevation data agreed very closely with the recalculated total having deleted a single track point and gives some validation to the number.

Image

I'd be interested to see if you get the same results and if your recalculated data is close to what you expect. If the results are consistent, simply deleting a single track point could be a relatively painless way to get a more accurate estimate of total ascent.
Last edited by Spiney on Sat Jun 15, 2019 12:01 am, edited 1 time in total.

gpsrchive
Site Admin
Posts: 376
Joined: Fri Jan 20, 2017 11:29 pm

Re: Total ascent figures

Post by gpsrchive » Sat Jun 15, 2019 12:00 am

pedigree1 wrote:
Fri Jun 14, 2019 6:04 pm
Many thanks.
oldkingog wrote:
Fri Jun 14, 2019 7:11 pm
Grateful for your work! I look forward to hearing what you learn...
I may need a week or two to get those tests started. You'll understand why soon.

pedigree1
Posts: 19
Joined: Wed Jun 12, 2019 9:48 am

Re: Total ascent figures

Post by pedigree1 » Sat Jun 15, 2019 9:42 am

Spiney wrote:
Fri Jun 14, 2019 11:59 pm
I have just read BLTAAKE's comments about the difference between the Trip Computer on Garmin devices and the GPX Track Log at https://forums.garmin.com/apps-software ... n-basecamp
In the past, there has been a confusion about why the Trip Computer data differed from the downloaded track log. Garmin has made two changes to their devices to address this. One is they made the Trip Computer a little smarter. It no longer logs every position solution, but only those where it decides the device has changed locations. This improved the total distance travelled, particularly for those just meandering about. The second change was to include the Trip Computer summary data with the downloaded Trip Log data.

This second change means that you no longer see summary data based on the data in the track log, but that of the trip computer. So, the device and BaseCamp agree exactly; but in truth, this is not a good thing to do.

If you are seeing Trip Computer summary data in BaseCamp, you can force recalculation based on the logged track data by deleting a single point in the track or dividing the track and then rejoining the track fragments. The former removes one data point, the latter adds one data point. The added point is a duplicate of one of the original track points.
If you follow the advice given and simply delete a single track point in BaseCamp, the improvement in accuracy of the cumulative ascent is staggering. I tried this for the track from a recent bike/hike in Scotland:

Original GPX loaded into Basecamp - ascent 2622m (WAY TOO HIGH!)
Image

Same file with trackpoint 3 deleted to force a recalculation - ascent 1890m
Image

This new figure is much closer to what I was expecting based on the map and guidebook.

Presumably Garmin's second change noted above also applies to FIT files too? I took a look at the FIT file for the walk:

I could not import the original FIT file for this hike directly into BaseCamp, so I had to convert it to a GPX first using GPSVisualizer. The initial converted GPX file had no elevation data, so I converted the FIT file again but adding elevation data from the GPSV's best digital elevation model. I then imported this new GPX file into BaseCamp. The 1880m total ascent using GPSV elevation data agreed very closely with the recalculated total having deleted a single track point and gives some validation to the number.

Image

I'd be interested to see if you get the same results and if your recalculated data is close to what you expect. If the results are consistent, simply deleting a single track point could be a relatively painless way to get a more accurate estimate of total ascent.
Thanks for that, very interesting! I tried your suggestion with a .fit file (recorded with v3.0 firmware) i.e. deleting a single track point in Basecamp. This took out 4m of ascent but reduced the total ascent by 100m and to much closer to the expected.
However, my issue has always been that the ascent data displayed on the unit during a hike is incorrect; it is this live data that I am more concerned about. Correcting the figures post hike is relatively easy, I can do this in other ways, it is the live feedback error that rather negates the reason for carrying the GPS unit in the first place.

oldkingog
Posts: 31
Joined: Tue Jan 08, 2019 6:01 pm

Re: Total ascent figures

Post by oldkingog » Sat Jun 15, 2019 11:34 am

[/quote]

Thanks for that, very interesting! I tried your suggestion with a .fit file (recorded with v3.0 firmware) i.e. deleting a single track point in Basecamp. This took out 4m of ascent but reduced the total ascent by 100m and to much closer to the expected.
However, my issue has always been that the ascent data displayed on the unit during a hike is incorrect; it is this live data that I am more concerned about. Correcting the figures post hike is relatively easy, I can do this in other ways, it is the live feedback error that rather negates the reason for carrying the GPS unit in the first place.
[/quote]

I couldn't have said it any better than pedigree. Definitely appreciate the tip, though!

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