Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

Discussion related to the Garmin GPSMAP 66sr GPSr
mimichris
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Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

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Garmin GPSMAP 66sr: Assessment of Its GNSS Observations and Centimeter-Accurate Positioning
In 2020, Garmin released one of the first consumer devices with a dual-frequency GNSS chip and a quadrifilar helix antenna: GPSMAP 66sr. The device is intended to serve as a positioning and navigation device for outdoor recreation purposes with positioning accuracies on the few meter level. However, due to its highly accurate GNSS dual-frequency carrier-phase observations, the equipment can also be used for centimeter-accurate positioning.
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GPSrChive
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

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Fantastic find!

Thank you for sharing!
Scenicsurfer
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

Unread post by Scenicsurfer »

Indeed a thorough and extensive research! This makes every owner of the 66sr proud.
Gadwin
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

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You can also read in this article, what I earlier described already, that the GPSMAP 66sr prioritize more the GPS satellites than the Galileo satellites. Would they change this setting, the device would be even more powerful.
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

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Gadwin wrote: Sat Feb 11, 2023 6:52 pm You can also read in this article, what I earlier described already, that the GPSMAP 66sr prioritize more the GPS satellites than the Galileo satellites. Would they change this setting, the device would be even more powerful.
This was true for their testing observations using a GPSMAP 66sr with firmware version 3.30 loaded.

The GPS Chipset software version at that time was 2.00.05, and there have been multiple updates to the device firmware and the GPS chipset software since then.

A new test would have to be conducted to definitively determine if any changes have been made to constellation priority.

We do recall many users indicating difficulty receiving Galileo signals during that time, and recent updates have improved this behavior considerably, so it would not be a huge stretch to assume a prioritization improvement has occurred.
mimichris
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

Unread post by mimichris »

I don't notice any difference with the new firmwares, (2.00.11)the number of Galileo satellites is still less than the GPS satellites, while the Galileos with my smartphone are on average 10 E1 and 8 E5a, I guess the 66sr only chooses the satellites Galileo multiband E1 and E5a because we always only see those.
Except for the GPS satellites we see the two of which those which are not multi-band and those L1 which are L5, why this difference in process?
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

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Last time we looked at our GPSMAP 66sr Satellite page, we were seeing more Galileo than GPS.

Likely related to what is available for the users current position and time, which will always be variable.

Will post some screen captures after we can check again.
mimichris
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

Unread post by mimichris »

Here's what I have: GPS always has more satellites than Galileo.


satellites
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

Unread post by GPSrChive »

A quick observation after looking at your screen captures:

More than twenty years ago, many GPS receivers were serial devices. These devices had a limited number of 'satellite signal channels'. They would listen for a signal, capture some data from it, then listen for another, do the same, and repeat. These devices did not have great accuracy or update rates.

The original Garmin Oregon x00/x50 and Colorado x00 series were parallel devices, each equipped with 12 channel receivers. These models could use as many as 12 satellite signals simultaneously. This does not mean they were all used to calculate the device location.

Then in 2011 Garmin introduced the worlds first consumer device that was able to simultaneously receive both GPS and GLONASS satellite signals. This was accomplished in part by increasing the number of available channels in the GPS chipset from 12 to 24. These models could monitor as many as 12 signals from both constellation in real time.

Most new models since have featured similar function, some allowing the user to choose between GLONASS and Galileo for the 'additional' constellation. 24 channels, two constellations, 12 channels each.

More recently, Garmin have again increased the total number of channels available for satellite signal monitoring in some models, allowing them to receive signals from many constellations simultaneously. The GPSMAP 66sr is one of these models.

Concentrating on the GPS and Galileo satellite pages, one can count the total number of monitored satellite signals for each constellation, and the total for each is twelve!

Fortunately, six of the twelve Galileo signals are in the 'E5a' band, compared to only two of the GPS signals in the 'L5' band. This already appears to be slightly biased toward Galileo at the moment these screen captures were taken, but this will always vary based on each constellations configuration at any given time.

While Garmin is not likely to divulge specific satellite signal monitoring strategies to the public, once can assume they are 'picking and choosing' only the 'best signals' from each constellation that can be used to provide the user with the most accurate and precise location information possible.
Gadwin
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Re: Garmin GPSMAP 66sr and Centimeter-Accurate Positioning

Unread post by Gadwin »

So does it mean, if I turn off Multi-band then I should receive more Galileo Satellites? Of course without Multi-band it is worse, but just out of curiosity.

What is the reason, that there aren't 12 GLONASS signals? I mean it is also a GNSS.
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