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When creating a track from map data in Basecamp, the elevations do not match the elevations shown on screen

9888201
over 2 years ago

I have a garmin GPSMAP 66SR with a local map installed connected to my computer via USB cable. The map on the GPS shows up on the screen in BaseCamp. But when I set selected track to Map elevations, or I create a new track, the elevations in the file come up very different from that shown on the map.  The map would for instance show 180m but the track file show 513m. The difference does not fit with a mater to feet conversion, so I don't think that is the issue.
Any advice would be greatly appreciated.

Also - is there an easy way to adjust the elevation of an entire track when the datum for instance is shifted?

  • 0 over 2 years ago

    The short answer to the second question is no.

    Regarding the first question, someone would have to know and have installed the map you are using in order to even begin trying to figure out what is happening.

  • 0 over 2 years ago in reply to BTLAAKE

    Thanks for feedback.

    I will go back to the Garmin shop where the GPS was bought as they installed the map. 
    Sad that BaseCamp can't perform such a simple operation - I assumed that I just couldn't work it out.

  • 0 over 2 years ago in reply to 9888201

    BaseCamp is capable of correctly assigning map elevation data to a track file as well as creating tracks with the map elevation data added.

    In your case, it could be a map issue or a workflow issue.  Garmin would expect a third party map to be referenced to WGS84 and the digital elevation model to use the units meters.

    As hypothetical example of a workflow issue, BaseCamp might not allow changes to the current track log.  It may or may not allow changes to a track saved from the current log on device.  If it doesn't, the export file might export the unchanged file on the device versus what you see on the screen.  Proper workflow would be to download the track, do the assign map elevation step on the track saved in BaseCamp, then export the BaseCamp track and or upload it to the device.

    However, I can't see why there should be a problem creating a track using the map elevations.

    Regarding changing elevations from one datum to another; it would require a geoid height model for each datum.  I'm not sure such models even exist. Your device requires a model for WGS84, but I wouldn't think that BaseCamp would require one for the functions it provides.

    Regardless of your choice of datums or units, gpx files will always have elevation in meters and WGS84 Lat/Lon.

    As to why the track log elevations are off by large amounts it is likely failing to calibrate the barometric sensor.  Your device will log elevation based on the barometric pressure sensor.  You can set barometric pressure mode to fixed elevation in the altimeter set up; the device will then log an msl elevation using the ellipsoid height and geoid height model.