GPSrChive Discussion Forum

pxl wrote: Sat Apr 22, 2023 9:04 pm

[...]
3) elevation is all over the place. after a calibration (to a precise altitude) it wanders by 50-100m (!) in the next ten minutes, so there were always a high jump in the middle of the elevation graph. I've tried all options (auto calibration), but it is all the same (maybe I don't understand how it works)
[...]

As far as I know auto calibration should be off otherwise it will calibrate on a regular base and as far I am aware it will use the altitude provided by the GNSS system, which is less precise than the barometer. I made the experience, that the altitude reading by the GNSS system is accurate as long you are standing on a really good point like on top on a mountain, but it will provide less accurate data in other situations.

So it is better to use the barometric altimeter on the device, but you have to calibrate it before you start to your currently known altitude. If you have a really good gnss signal, then you can calibrate to your altitude given by the gnss system. Of course the data by the barometric altimeter will be unstable if the weather is not stable, what is good indication that a storm might be coming.

pxl wrote: Sat Apr 22, 2023 9:04 pm 3) elevation is all over the place. after a calibration (to a precise altitude) it wanders by 50-100m (!) in the next ten minutes, so there were always a high jump in the middle of the elevation graph. I've tried all options (auto calibration), but it is all the same (maybe I don't understand how it works)

Recommended calibration settings - Once allows the altimeter to automatically calibrate one time when you start an activity, make sure that there is no Curent Track in the receiver, so I suggest disabling the autostart option. When the GPS signal is weak, manual calibration can be used if the altitude above sea level is known. You can set the Elevation GPS and Elevation data fields, the first will display the altitude data
based on GPS data, the second value will be based on the altimeter. Until the track recording is switched on, both indication values will be the same - data from the GPS signal, after switching on the recording, the data displayed in both fields may differ.

pxl wrote: Sat Apr 22, 2023 9:04 pm I've just finished a daily hike testing exactly this question. (23 km, 5 hours moving time, trip time 9 hours).....

I've created a gpx file and uploaded to the GPSMAP 67, to Fenix 6X pro and Forerunner 265 to check the usability, gps accuracy and the overall usefulness.

First, the data:
Trip lengths:
265: 24.28 km
Fenix: 29.99 km
GPSMAP: 23.30 km

The difference in the distance indication may be due to different settings of the track recording interval. It is not known the program in which the trace was read, whether it was the same program. It happens that the same track read in Base Camp and MapSource can differ significantly.

The reason may be an additional entry in the .gpx file "<gpxtrkx:TrackStatsExtension xmlns:gpxtrkx="
in which the distance "<gpxtrkx:Distance>29055 is written </gpxtrkx:Distance>" The value provided in this sequence does not match the actual distance.

Why the notation is added, under what circumstances, and where the distance value in this sequence comes from,
is probably not fully explained.

Thanks for the tips regarding the elevation accuracy! However, I miss the option to calibrate the elevation to DEM data (the Fenix has this option).

Probably the reason why the elevation went sideways was the weather. When I started it was full sunny, later it was full cloudy, then sunny again at the end. There were no rain or storm, though.

The trip length data came from the Garmin Connect in all cases (there is no Distance xml element in the gpx files) - and I think this picture could reveal the reason behind the difference. I was just sitting in one spot (well in 2 spots, there and back)

*** Hotlinked Image Removed ***

It seems to me that the GPSMAP did very well (it was a under a somewhat dense canopy, in a shallow valley, 1 spent approx 10 minutes in both cases).

pxl wrote: Sun Apr 23, 2023 8:51 pm Thanks for the tips regarding the elevation accuracy! However, I miss the option to calibrate the elevation to DEM data (the Fenix has this option).

Probably the reason why the elevation went sideways was the weather. When I started it was full sunny, later it was full cloudy, then sunny again at the end. There were no rain or storm, though.

The trip length data came from the Garmin Connect in all cases (there is no Distance xml element in the gpx files) - and I think this picture could reveal the reason behind the difference. I was just sitting in one spot (well in 2 spots, there and back)

*** Hotlinked Image Removed ***

It seems to me that the GPSMAP did very well (it was a under a somewhat dense canopy, in a shallow valley, 1 spent approx 10 minutes in both cases).

What do the different colors correspond to, Thank you.
If you take a break while hiking, it is better to put the GPS on pause, it will avoid this kind of scribbles that give distance.

pxl wrote: Sat Apr 22, 2023 9:04 pm
TL;DR: I've found the GPSMAP is much better in every aspect than a watch.

This device is made for trips. The antenna itself is the size of many watches . He will always win with watches.
Handheld devices are not a priority at Garmin, so don't expect a better design .

My Epix and GPSMAP 67 (set to 1-second recording intervals) lay similar tracks. I don't know which one is more accurate. I use to think the Epix was, but I'm not so sure anymore. Here is an example under a tree canopy on a mountain bike. Overcast with recent rain (foliage is wet).

Spoiler

Screenshot_20230424_065144_Explore.jpg

MarkHL wrote: Mon Apr 24, 2023 2:06 pm My Epix and GPSMAP 67 (set to 1-second recording intervals) lay similar tracks. I don't know which one is more accurate. I use to think the Epix was, but I'm not so sure anymore. Here is an example under a tree canopy on a mountain bike. Overcast with recent rain (foliage is wet).

Spoiler

Screenshot_20230424_065144_Explore.jpg

I don't know which one is better either. For the test to be reliable, you must perform it consciously. The recording parameters should be at least close. The route is planned, you are moving along a fixed line. With the assumption 67 should be better than a watch, if it is not .... It remains to wait for improvements, maybe they will come.