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Elevation recording

Posted: Fri Jan 05, 2018 9:10 am
by Mick F
I took my Montana on a flight last month and recorded the flightpath. Trouble was, the recorded elevation was dictated by the cabin air pressure and the "altitude" levelled out at 20,000ft ................... instead of the GPS readout at 38,000ft.

Is it possible to record the raw GPS elevation rather than BP?

Thanks,
Mick.

Re: Elevation recording

Posted: Fri Jan 05, 2018 2:30 pm
by GPSrChive
Try:

Setup > Altimeter > Auto Calibration > On
Setup > Altimeter > Barometer Mode > Fixed Elevation

Re: Elevation recording

Posted: Sat Jan 06, 2018 6:52 am
by Mick F
Thanks for the reply.

I'll have a play with Monty later, but one thing puzzles me. On the Trip Computer page, I have one section displaying elevation. This elevation readout is BP elevation which is also influenced with GPS elevation. I calibrate the elevation at home at 222ft to force it correct. If I didn't calibrate it and left Monty outside for a some time, it would eventually drift to 222ft automatically.

By setting the Altimeter in Setup like you suggest, would the Elevation readout in Trip computer be exactly the same as GPS elevation? I can set one of the Trip Computer data fields to display GPS elevation of course. Would this GPS elevation now be the one that is recorded?

As I say, I'll have a play later today or tomorrow.

Thanks,
Mick.

Re: Elevation recording

Posted: Sat Jan 06, 2018 7:33 am
by sussamb
GPS elevation will always vary from any barometric reading

https://support.garmin.com/faqSearch/en ... yoxITW2vZ6

Re: Elevation recording

Posted: Sat Jan 06, 2018 12:06 pm
by Mick F
sussamb wrote: Sat Jan 06, 2018 7:33 am GPS elevation will always vary from any barometric reading

https://support.garmin.com/faqSearch/en ... yoxITW2vZ6
That's the point.

BP altimeter will always be at variance with GPS, especially if you are in a pressurised cabin on an aircraft at 38,000ft. ;)

My question was about how to record the GPS elevation instead of the BP elevation.

However, leave your Montana in the open, and eventually the BP will be very close to GPS elevation.

Mick.

Re: Elevation recording

Posted: Sat Jan 06, 2018 12:31 pm
by GPSrChive
Mick F wrote: Sat Jan 06, 2018 6:52 am By setting the Altimeter in Setup like you suggest, would the Elevation readout in Trip computer be exactly the same as GPS elevation? I can set one of the Trip Computer data fields to display GPS elevation of course. Would this GPS elevation now be the one that is recorded?

As I say, I'll have a play later today or tomorrow.

Thanks,
Mick.
I have successfully (in the past) recorded many flights using a Montana GPSr and I believe those are the settings I used. You will need to be seated near a window and keep the GPSr as close as possible to that window for best satellite reception.

Re: Elevation recording

Posted: Sun Jan 07, 2018 6:12 am
by Mick F
Tried it out and it works!

Set the Altimeter to "Fixed Elevation" in Setup/Altimeter/Barometer Mode.

BP Elevation will now be equal to GPS Elevation, so when you produce your GPX track in Track Manager, the elevation profile is the GPS elevation profile. This means then when I go on a flight again, I can record the correct height of the flight and not one that is corrupted by the internal cabin pressure.

Thanks very much indeed.

Mick.

Re: Elevation recording

Posted: Sun Jan 07, 2018 2:37 pm
by GPSrChive
You're welcome!

Happy GPSring!

Re: Elevation recording

Posted: Thu Nov 29, 2018 11:46 am
by Mick F
Mick F wrote: Sun Jan 07, 2018 6:12 am Tried it out and it works!

Set the Altimeter to "Fixed Elevation" in Setup/Altimeter/Barometer Mode.

BP Elevation will now be equal to GPS Elevation, so when you produce your GPX track in Track Manager, the elevation profile is the GPS elevation profile. This means then when I go on a flight again, I can record the correct height of the flight and not one that is corrupted by the internal cabin pressure.

Thanks very much indeed.

Mick.
Well ..................

On a flight last week to Bristol to Alicante and back - both journeys with my Montana set up as per the above instructions. The BP altimeter was the same as GPS altimeter as read on Track Manager.

However, when I uploaded the tracks onto my Mac and viewing the flight profiles, they both level out at 20,000ft despite the flight there being at 36,000odd feet and the flight back being at 39,000odd feet.

Thanks,
Mick.

Re: Elevation recording

Posted: Thu Nov 29, 2018 1:43 pm
by GPSrChive
Mick, can you send me those GPX files?