GPSMAP 66 Firmware 6.00

Discussion related to the Garmin GPSMAP 66s/st GPSr
Skinoku
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Re: GPSMAP 66 Firmware 6.00

Unread post by Skinoku »

Thank you very much for all this information.
As soon as the pandemic is over I will go out with my 66s try to figure out how this works and maybe find the way it is behaving especially in Automatic altitude calibration mode. Many Thanks for Now
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GPSrChive
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Re: GPSMAP 66 Firmware 6.00

Unread post by GPSrChive »

I hope that happens very soon and am looking forward to reading about your observations.
Spiney
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Re: GPSMAP 66 Firmware 6.00

Unread post by Spiney »

gpsrchive wrote: Mon Jan 04, 2021 3:11 pm Unfortunately, Garmin does not publish any detailed information about how 'Auto Calibration' functions on their devices, and I suspect it likely does not operate in the exact same fashion from one device to the next. Essentially, when set to 'Continuous', the GPSr is deciding 'if' and ' when' to calibrate the altimeter based on unpublished variables.
Garmin have disclosed some details of the basic method they use for autocalibration in US Patent No. 7,142,152 "DEVICE AND METHOD FOR CALIBRATING AND IMPROVING THE ACCURACY OF BAROMETRIC ALTIMETERS WITH GPS-DERIVED ALTITUDES" https://patentimages.storage.googleapis ... 142152.pdf

This might provide some useful insights for investigating the issue further.
Hiker
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Re: GPSMAP 66 Firmware 6.00

Unread post by Hiker »

My observations with respect to the automatic calibration of the barometric altimeter in continuous mode let me conclude, that this feature simply does not work. This has been the case through all FW releases. Fortunately we are free to go hiking during the pandemic. The barometric altimeter sticks to the barometric pressure. During long hikes under changing weather situation, the deviation between barometric and GPS-altitude steadily increases. I finally put the GPSr in small vacuum chamber and gradually reduced the barometric pressure in the test chamber according to an increase in altitude of 200 metres. There was no sign of both figures converging. The difference of both readings did not vary. So there is no continuous calibration.

By the way continuous means steady over time and not at obscure intervals, not laid open by GARMIN. I've reported the issue several times to GARMIN. They are ever so forthcoming and helpful, nevertheless the issue perpetuates, which is frustrating.
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GPSrChive
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Re: GPSMAP 66 Firmware 6.00

Unread post by GPSrChive »

Hiker wrote: Sun Jan 10, 2021 5:19 pmI finally put the GPSr in small vacuum chamber and gradually reduced the barometric pressure in the test chamber according to an increase in altitude of 200 metres. There was no sign of both figures converging. The difference of both readings did not vary. So there is no continuous calibration.
How long was the device left in the 'vacuum chamber'?

As I understand it, the Garmin devices constantly compare the barometric elevation values against the GPS elevation values, and should the device experience a change in pressure that does not coincide with the GPS based elevation data, the device will not alter the elevation calibration value, instead assuming the change in pressure was an anomalous event.

The barometric sensor in your Garmin GPSr is not of the highly precise test instrument variety, although they are more than capable of tracking changes in elevation based on change sin ambient pressure. All modern Garmin GPSr allow the user to fine tune this by calibrating the current elevation for the pressure the device is recording, and this variable will be slightly different from on device to the next.
Hiker
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Re: GPSMAP 66 Firmware 6.00

Unread post by Hiker »

Many thanks for your immediate response and your keen interest.

The device was left for two hours at the altered ambient pressure.

You stated, the device would not change the barometric calibration value when pressure changes and GPS-altitude not changing accordingly. In my humble opinion I would assume that "Continuous Calibration" would align the barometric altitude to the GPS-altitude. If not so, the question arises why the option of "Continuous Calibration" is offered as an option.

The idea behind the vacuum chamber was to keep one set of variables constant and just to vary the other one, to see the response. Or equally, I had a lengthy hike at the sea side with barometric and GPS altitude diverging, whilst I was close to sea level. On my return there were about -150m difference in a altitude on the spot of departure without me being drowned. During my hike the weather situation changed.

I've seen my GPSMAP performing duly with respect to the above. As to the GPSMAP 66st, I'm reminded of the emperor's new clothes.
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GPSrChive
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Re: GPSMAP 66 Firmware 6.00

Unread post by GPSrChive »

Hiker wrote: Mon Jan 11, 2021 1:34 pm The device was left for two hours at the altered ambient pressure.
Might you have access to additinoal Garmin GPSr with ABC sensors to perform the same test?

All scientific testing requires a 'control.'

Testing one more device is not exactly a 'control', but performing the same test on multiple devices could potentially show a behavior that is deviated from the 'norm.'
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GPSrChive
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Re: GPSMAP 66 Firmware 6.00

Unread post by GPSrChive »

Hiker wrote: Mon Jan 11, 2021 1:34 pm You stated, the device would not change the barometric calibration value when pressure changes and GPS-altitude not changing accordingly. In my humble opinion I would assume that "Continuous Calibration" would align the barometric altitude to the GPS-altitude. If not so, the question arises why the option of "Continuous Calibration" is offered as an option.

The idea behind the vacuum chamber was to keep one set of variables constant and just to vary the other one, to see the response.
As I understand it, the Garmin GPSr uses the GPS Elevation value to confirm when atmospheric pressure changes are a result of actual elevation change and not a result of a change in weather conditions.

Changing the atmospheric pressure value seen by the GPSr by placing it in a vacuum chamber did not fool the GPSr because it was using the GPS Elevation value to verify any actual change in elevation, of which there was none. In your test, the GPSr performed exactly as it should.

Hiker wrote: Mon Jan 11, 2021 1:34 pm Or equally, I had a lengthy hike at the sea side with barometric and GPS altitude diverging, whilst I was close to sea level. On my return there were about -150m difference in a altitude on the spot of departure without me being drowned. During my hike the weather situation changed.
In this scenario, you would have wanted to use the 'Auto Calibration = Once' option under Altimeter Calibration, which would have resulted in the starting and ending hike elevation values being nearly identical. The altimeter would have only calibrated one time shortly after power on, then recorded all elevation values for the duration of the activity based on that calibration.

Using the 'Auto Calibration = Continuous' option allows the GPSr to make constant adjustments to recorded elevation values based on atmospheric pressure changes that are verified against changes in reported GPS elevation values.
Hiker
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Re: GPSMAP 66 Firmware 6.00

Unread post by Hiker »

Heiio again

I tried "Auto Calibration = Once". The device did not get a near correct barometric altitude upon power-up. The figures were: GPS = 103m (correct) and barometric 195m. I would not argue that your observations were not authentic. With the internals of the firmware not laid open, it is no doubt difficult to assess, if a positive response in one case is an a priori verification holding valid in all future cases.

I tried work arounds that seemed to do the trick temporarily. However the only way so far is to manually calibrate the altimeter.
987
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Re: GPSMAP 66 Firmware 6.00

Unread post by 987 »

Hi.
The auto calibration = once is location dependent and seems to require one good manual calibration first.

To see how it works:
set auto calibration = once.
Start at a known location, say at home, where you know the altitude.
Make sure that the unit has a GPS connect and has a position reading.
Manually calibrate the altimeter and set the elevation.

Next time when you are in this location, if you reset the the recording via the Recoding control -> Discard (or perhaps on a unit start), the unit will set the elevation, it will be the same that you once set.

You can do this for multiple places which the unit will remember (i have two locations which i frequently use), but i cant say how well it works for a random location at which i did not know the elevation at least once.
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