Total Ascent Values Exaggerated by 50% [Bug 29]

[dhg]

Hi, I have a gpsmap 67 (v6.60) and recently noticed that each time I use it the ascent / descent feet counter is over recording by about 50%. I typically walk ~12 mile walks and total expected gain on a recent one was around 1300 feet but by the end of the walk the ascent / descent count was over 2000 feet. In google Earth the recorded track shows Elev Gain/Loss at 1351 feet for the walk and the route is officially 1361 feet, so the amount recorded in the track is as expected, but the screen is counting over 2000. At first I thought this was just a random GPS drift issue but the track shows the route recorded accurately and this same issue is happening everytime I use the device.

Many thanks

Don.

[RickN55]

+1 with this issue, I've also noticed how well out the altimeter is on the 67, I regularly do the same 3 miles walk daily which is mostly flat, my 67 says I've done just over 600 feet ascent and descent each time, but there are barely any hills, my Epix gen 2 pro sapphire and my gpsmap 65s has the same route at around 90-100feet ascent and descent each time.

I am on the latest firmware also.

[dhg]

Hi pls find a zip attached. It includes the route I created in Basecamp and the track I created on the walk with the 67.

Cheers.

Don.

*** please review forum posting guidelines ***

GPX Files

MyWorthWay.zip

[Przekątny]

Hi, I have a gpsmap 67 and recently noticed that each time I use it the ascent / descent feet counter is over recording by about 50%. I typically walk ~12 mile walks and total expected gain on a recent one was around 1300 feet but by the end of the walk the ascent / descent count was over 2000 feet. In google Earth the recorded track shows Elev Gain/Loss at 1351 feet for the walk and the route is officially 1361 feet, so the amount recorded in the track is as expected, but the screen is counting over 2000. At first I thought this was just a random GPS drift issue but the track shows the route recorded accurately and this same issue is happening everytime I use the device.

Check the Auto calibration setting, there are two options, automatic calibration when turned on - the altimeter is calibrated once based on the GPS signal, in further operation only pressure changes affect the readings.

Second option: Continuous mode - the altimeter is calibrated throughout the duration of the activity; when using the Continuous mode option, the altitude indications are influenced by changes (signal fluctuations) in the GPS signal reception, which may increase the value of ascents and declines.

It is possible to set the data fields in the device, GPS altitude and altitude, when the calibration option is turned on, the data values in both fields may differ, if there is difficulty in receiving the GPS signal, the value in the GPS altitude field may change,but it will not affect the data value in the Height field.

The altimeter's readings are influenced by the air temperature; when traveling through a tree-covered area, there may be even several-degree differences in temperature, which affect the pressure,
which translates into the altimeter's readings causing an overestimation.values of ascents and descents.

Another thing is that the indications of the values of rises and falls are questioned by users of various devices.

[dhg]

thanks, mine is set to 'Once'. I've recalibrated so I guess I'll see if that makes any difference.

[Przekątny]

The data recorded in your track differs from the ascent and descent values provided by the DEM data contained in the map, but also differs from the data displayed in the track properties in Base Camp.

The ascents calculated based on the recorded data are 432 m and not 603 m as displayed in the track properties in Base Camp, the descents are 415 m and not 587 m as displayed.

The difference in values is caused by the entry in the TrackStatsExtension sequence, the sequence is created by the device software, I cannot explain why an inflated value was entered in the TrackStatsExtension sequence.

[dhg]

Thanks for your reply. So are you saying that's something I can change, or something that's been coded into the firmware that Garmin would need to change? If the former what do I need to do, if the latter, are Garmin aware of the problem?

Many thanks.

Don.

[GPSrChive]

Garmin software engineers have been notified, but you should also open a ticket with Garmin Support.

"The squeaky wheel always gets the oil..."

[Przekątny]

Thanks for your reply. So are you saying that's something I can change,.......

You can improve it yourself:
If you are satisfied with the value of ascents and descents calculated on the basis of the map's DEM data, you can add the DEM data to your track - Base Camp allows this option.

In case you prefer the values of ups and downs calculated
based on the data stored in the trace, you should load the trace
to a program that ignores the TrackStatsExtension sequence (MapSource),
save to a gpx file, then load into Base Camp.

You can also remove the TrackStatsExtension sequence from the track record by editing the gpx file.

[dhg]

Many thanks, but you're assuming a level a knowledge way beyond what I have or intend to develop. I just want the device to work, not for me to have to mess around with a load of arcane parameters hidden around the device and files. I'm told the issue has been raised with Garmin support.