[Tagging] How to tag for dualband GPS ?

Lindsay Barnes newsspeak11 at gmail.com
Mon Nov 30 14:41:36 UTC 2020


I recently wrote a series of diary entries about my experience with the
accuracy of one-device GPS precision. I concluded with a comparison of
three devices I had personal experience with including a new Garmin GPSMAP
66sr which I posted here:
https://www.openstreetmap.org/user/bobwz/diary/394711

In short, multi-band and multi-GNSS devices do offer in an increase in
precision and accuracy and we're seeing this become more common in a
standard smartphone. However, that level of precision is not necessary in
most cases. It is most helpful in areas without good satellite imagery
coverage or where imagery lacks reference points (like in wooded trail
areas, as mentioned). This is compounded by the fact that one GPS device
has a floor to how accurate it can be due to the nature of the system and
interference from the natural landscape, as was mentioned. Furthermore,
mult-band and mult-GNSS chips are becoming more common in smartphones and I
would expect this level of precision available to most mappers without the
need for specialty equipment over the next 5-ish years.

To answer your question about tags, a comment can be added in the source
field of a changeset, but in my opinion most mappers will not dig too deep
into a change to determine how precise the mapper may have been . Satellite
imagery is generally used as the source of truth and if a mapped feature
varies substantially from the imagery, mappers are inclined to move the
feature to match imagery without researching how the feature was initially
created. The good news is that if satellite imagery in unclear or lacks
reference marks, mappers will usually leave features alone unless they have
personal knowledge of an area or are working off a tasking manager.

On Mon, Nov 30, 2020 at 8:36 AM Andrea Mazzoleni <amadvance at gmail.com>
wrote:

> On Mon, Nov 30, 2020 at 12:27 PM Warin <61sundowner at gmail.com> wrote:
>
>> If the intention is to indicate the error/accuracy/uncertainty then
>> tag/state that. The better GPS devices give indications of this
>> error/accuracy/uncertainty.
>>
> The big advantage of the dualband is not (only) the increase in accuracy
> but the ability to work in not optimal conditions, like under a clif or
> other obstacles where you have reflected GPS signals.
>
> To give you an example, my eTrex device reports 3m of precision, the new
> GPSMAP 65s reports 1.8m.
> But reality is that I saw errors up to 50m with the eTrex. It's also
> difficult to know the precision because it changes while moving, and it's
> not recorded in the track.
>
>> If possible take tracks of home to/from work and compare them to see how
>> much they vary day to day ... they should give an idea of problem.
>>
> I bought that new device exactly due the frustration of always seeing a
> different recording...
>
> My initial tests are really encouraging. Yesterday I repeated 10 times a
> trail under the woods of a hill, comparing the results of the eTrex and
> GPSMAP 65s, and the dualband one has the recorded tracks a lot more
> consistent. Something like 10m vs 2m thickness.
>
>> imagery may well be better than survey by consumer GPS
>>
> I agree. Where an image is available I always use it as reference. But
> most of the trails of my local area are under the woods (low mountain) and
> the GPS is the only source of information.
>
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>
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