Thread: Accuracy figure of horizontal position fix on GPSMAP 66 satellite screen?

The OP's question relates to accuracy and if the indication is CEP.

In the GPSMAP66sr other than the real time weather forecasts which are a different beast entirely, the inclusion of L5 is not real time atmospheric correction. It’s a good incremental step forward as the different wavelengths help in the same way that L1 & L2 have traditional done for pro grade dual frequency equipment.

And multi GNSS is great but the main benefits are quicker time to fix and more often able to get a reasonable position, the improved accuracy is incremental as it’s still code-based resolution and timing errors.

To get real step up in accuracy requires correction and processing against a known reference point, close by, and either from a true real time incoming data stream processed within the device or post processing later with sophisticated software. And it also requires breaking beyond the inherent limitations of code-based positioning which means working in carrier phase.

Garmin acknowledge this by providing an optional specialized RINEX/Carrier capability in the GPSMAP66 for sub-metre positioning.

I have a number of Garmin multi GNSS devices including GPS66i that I use for general navigation and display of JNX historic background maps when I am mapping with pro gear, and have been analyzing back-to-back comparisons of the results for many years as the Garmin equipment improves looking for opportunities however I have not seen suitable results yet.

I obtained the GPS66i in part because of it's RINEX / carrier phase capability and the promise of lightweight low grade accuracy mapping however my experience has been that it has not proven sufficiently accurate or practical as I had hoped.

And whilst it is technically multi GNSS (GPS & Galileo only, no Glonass the frequency interferes with the Iridium) it is still noticeably more susceptible to multipath and error than my older Rino 650's evidenced not only by the spiky jumping tracks but also in direct comparison of the static points to the Trimbles post processed data and known survey references at the cm level.

Don't get me wrong, I love all the devices and take them everywhere and particularly the GPSMAP66i with it's large clear bright screen, JNX & remote emergency capability.

But these devices are definitely not in the same accuracy and mapping league as pro grade equipment, you get what you pay for.

And if you really think the device only needs 4 or 5 satellites for a fix there is a serious disconnect with the accuracy discussion, you may want to play with the charts here to understand the relationship between the number of satellites and DOP: [Only registered and activated users can see links. ]

So to get back to the point of the OP question, unless you are utilizing the Garmin Rinex/Carrier functionality (not for the feint hearted) you won’t be anywhere near approaching sub-metre and the number of metres the device is indicating will most likely be 50% CEP.