GPSMAP 67 ELEVATION

What device software version are you on?

There have been more reports of people observing much higher total ascent values than logically make sense on the GPSMAP 67 series, myself included.

As you say the elevation readings are quite accurate but the ascent value displayed is not. 

I would suggest to report this issue to Garmin support, the more people report the better. I have done so as well.

Thank you JungleJim,

I had Etrex32x which works very well in altimeter mode.

With my GPSMAP67 it is not very clear.

Do you know where I can find a paper concerning altitude "permanent auto calibration"? How long to refresh? On what GPS élévation? 

For example GPS elevation is 35 meters, elevation on map is 18 meters , I enter 18meters in altitude calibration. One hour after GPS indicate 30 meters and altitude is always 18 meters. I don't understand how it works.

I had no problem with my etrex 32x

The Garmin support article https://support.garmin.com/en-US/?faq=FhOYuggxmV6Atph276U4h8 explains how the various calibration methods (should) work. I haven’t been able to find more detailed on how the calibration works exactly, only Garmin knows this.

Also it’s good to understand the difference between altitude, elevation and ascent: altitude is the height above ground level, elevation is the height above sea level, ascent is the vertical distance you have traveled upwards. The elevation reported by the GPSMAP is quite accurate in my experience. It’s the ascent that seems to have some issues. Altitude is something the GPSMAP does not report.

Another thing that’s good to know is that the GPSMAP 67 will update the total ascent data field (which you can use on the trip computer) even when not recording an activity (ie not started recording yet or pausing a recording). The ascent value in the activity will only include the ascent during the activity, though. So in other words, the value of the data field may differ from the summary value in the recorded activity depending on when you started recording and/or pausing. So it’s best to clear the trip computer just before starting your activity recording.

Make sure you are on firmware 8.50 by the way, as this seems to improve ascent reporting compared to previous firmware versions.

Thanks a lot for your answer. It will be clear now for me and i understand more how it’s works. Whats about of wgs 84 in all these mesurements?

Can't help you with the question on WGS84, maybe others can help with that. But curious why you want to know?

WGS 84 is a datum. it implies an ellipsoid. The ellipsoid is what determines "sea level" for the elevation reading. it is what is. The only thing to keep in mind is that choosing a different datum usually means a different ellipsoid. Which means that you may well get a different elevation reading at the same point under two different datums and identical calibration.

None of that has anything to do with calibration itself. Unless you use known elevation for calibration. Even then, it depends on where you get your known elevation.

Clear as mud, right?

Thanks a lot

It means that WGS84 is reference 0 meters through the world. I suppose Garmin use that ellipsoid on set up. My gps67 is on WGS84 Am I Right??

I believe the default is WGS 84. This is the native datum for GPS. You can change it. Main menu > Settings > Position Format. You can change the datum, which automatically selects the correct spheroid (aka ellipsoid). 

The ellipsoid is an egg-shaped solid which approximates "sea level" everywhere. It is just an approximation, of course.

Generally, there is no reason to change the datum. There are excerptions when using the device with external paper maps. For example, older paper USGS 7.5 minute topos use the datum NAD27 CONUS. But that's a really unusual use case. Certainly, as long as you are using only the maps on the device itself, WGS84 is fine.

As long as we are going into way more detail than necessary, it's worth noting that datum also influences the latitude/longitude coordinates. At a given location, different datums will show slightly different coordinates. In some cases, the difference will be large enough to be noticeable - up to 10s of meters.

This is important if you are manually entering coordinates from an external source. For example, geocache coordinates on the web site are WGS 84. To get things right, the device must be set to the same datum as the coordinates when you manually enter the coordinates. If you then change the datum, the device automatically converts the coordinates to the newly selected datum for display.,

Again, clear as mud. In almost all cases, you can just leave the device set to WGS84 and everything just works.

Afaik the GPSMAP 67 does not use DEM data from maps to calibrate altitude. Garmin smartwatches do indeed have this feature, and it would be nice if Garmin would add it to the GPSMAP.

You can suggest this feature at the form here: https://www.garmin.com/en-US/forms/ideas/

No guarantee that Garmin will listen but the more people suggest this idea, the better the chances.