GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Discussion related to the Garmin GPSMAP 66sr GPSr
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GPSrChive
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by GPSrChive »

I performed a test this morning with my 66sr, which had not been powered on for many days.

First, I connected the 66sr via USB and deleted the CPE.BIN file.

After rebooting the 66sr, 'Setup > About' showed 'CPE: Missing', and the Satellite page was searching for available signals with no position reported.

The GPSMAP 66sr was located deep inside a concrete and steel building.

After less than three minutes, the 66sr was receiving GPS, GLONASS, and Galileo signals and reported a position with 6ft accuracy.

Rechecking 'Setup > About' showed 'CPE: Expired'.

I then enabled Bluetooth and connected to the Explore app on my phone, and after a complete sync was performed, 'Setup > About' showed 'CPE: Current'.

Total elapsed time: Less than 15 minutes.

CPE Test 66sr v520 220427.png
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mimichris
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by mimichris »

There is still a big difference in the number of satellites with the up-to-date CPE.BIN and without the up-to-date CPE.BIN, so theoretically we cannot have the same precision and the same quality of reception with and without the up-to-date CPE.
I had noticed that without current CPE the number of satellites was low.

You certainly have to wait long enough to have the same number of satellites without CPE as with CPE and to have the quality of reception, which is not the case with the 64s or other Garmins which do not use CPE.

I ask myself the question, namely that as soon as we have the satellites with the current CPE, which is almost instantaneous, we have the best precision, I think we have to wait a bit for the acquisition of the almanchs be complete.

On my smartphone, which has AGPS, the same as Garmin's CPE, you still have to wait a bit for the satellites to be completely acquired, seen on the "GPSTest" application.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
ewald.gruen
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by ewald.gruen »

There and back on a hillside path completely covered by vegetation and less than 30 cm wide:

64s_vs_65s_vs_66sr.png
mimichris wrote: Wed Apr 27, 2022 9:32 amupdating the almanacs on my 66sr is very, very long, after two hours, I do not have all the satellites visible that day and therefore the accuracy is feels.
To my understanding not having any almanac data does little to no harm on the 66sr, because a) by the time it takes to download the almanac a regular "sky search" should have already found all available satellites and b) guessing the ionospheric delay based on dual-frequency observations is most likely more accurate than the global ionospheric model which is included in the alamac, but: I had my 64s, 65s and 66sr on the windowsill all night today and got the following (disappointing) result:

gpsmap_position_error.png
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mimichris
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by mimichris »

Strange for the 64s which is not the best in terms of precision, I had it and at the time compared to my two Twonav Cross and Trail2 (GPS, Glonass and Galileo), it was as we say in France, in cabbage.

The 66sr should only be tested in normal mode, not multi-band.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
mimichris
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by mimichris »

Looks like Garmin has restricted the 66sr with maximum satellites, big mistake, on my multi-band smartphone I get at least 25-30 satellites including a dozen in multi-band. Why does Garmin restrict its GPS? It's a shame, is there an algorithm that only uses satellites with an excellent signal? But it's depriving yourself of others who can also improve your positioning.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
mimichris
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by mimichris »

"5. Conclusions and Outlook
The Garmin GPSMAP 66sr (v3.30) offers dual-frequency GNSS observations for cmlevel postprocessing applications.
Due to its quadrifilar helix antenna, the observation
quality exceeds the quality of other consumer devices with dual-frequency capability, e.g.,
smartphones. Centimeter-level positioning results can be achieved in long observation
sessions (several hours), with precise point positioning (PPP), or in short observation
sessions (many minutes) in baseline mode.
The main limitation of the device with respect to precise GNSS positioning is caused by
the incompleteness of the tracked satellite signals. In particular, a higher priority of Galileo
in the satellite selection process would considerably improve precise positioning results.
If this problem is solved and with an increasing number of active Galileo satellites and
more GPS satellites capable of transmitting G5 signals in the near future, the positioning
performance will even exceed the level demonstrated in our trials."
I'm right in saying that a lot of satellites are missing, especially Galileo very accurate, I hope garmin will correct this problem because we certainly lose signal quality in bad conditions.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
ewald.gruen
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by ewald.gruen »

Another (only 1 hour long) test where all three devices were flat next to each other on a desk right next to a window, and this time I permuted the position of the devices after every 20 minutes so that all devices were in the exact same position for the same amount of time:

gpsmap_position_error.png
gpsmap_position_error_pctl.png
mimichris wrote: Mon Jul 04, 2022 12:06 pmStrange for the 64s which is not the best in terms of precision[
I guess an outdoor test would show the difference, but the last time I tried both the 66sr and 65s couldn't pick up Galileo satellites, so I had to abort the test.
mimichris wrote: Mon Jul 04, 2022 12:06 pmThe 66sr should only be tested in normal mode, not multi-band.
I could do a test where only one of the two devices has "multi-band" enabled, but as far as I can tell, disabling it only makes the situation worse.
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mimichris
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by mimichris »

I did not do a fix test but in bike touring, I had the 64s and the Trail2 Twonav at the time, the 64s is sometimes bad next to the Trail2 especially in hairpin turns, the track deviates a lot. But this is normal since the Trail2 is GPS, Galileo and Glonass and therefore has many more satellites compared to the 64s which only has GPS and Glonass.
And yet on a bike the track is much better than on foot. Speed has a lot to do with it.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
ewald.gruen
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by ewald.gruen »

Another test (almost 1 hour long) in which all three devices were laid flat next to each other on a table in the middle of the balcony (20 x 20 m with a clear view of the sky) without permuting the positions of the devices:

gpsmap_position_error.png
gpsmap_position_error_pctl.png
gpsmap_track.png

Satellite pages:

66sr_satellite.png
65s_satellite.png
64s_satellite.png

Not quite what I expected to be honest. Am I stupid? Am I falling into a trap for young players?
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GPSrChive
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Re: GPS vs EXPANDED GNSS vs MULTI-BAND FREQUENCY in semi challenging conditions.

Unread post by GPSrChive »

Thank you, ewald.gruen, for posting these test results.

I am confident further GNSS software updates are in the 66sr future.
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