On 1/12/20 7:46 am, Andrea Mazzoleni wrote:
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
Very interesting!
Here you can find the mapping of my tests with GPSMAP 65s and eTrex 30x:
https://ibb.co/bKvpxYG
It's a circular trail repeated 5 times with one point every second.
I repeated it again with the recording frequency set to Auto, and the
GPSMAP lost a bit in accuracy, so better to stick to one point every
second.
Think your confusing two terms;
resolution
accuracy
With increased points along a way there is increased resolution.
The accuracy does not follow with increased number of points unless they
are all for the same location so averaging those points reduces noise
thus increasing accuracy.
On Mon, Nov 30, 2020 at 3:45 PM Lindsay Barnes <newsspea...@gmail.com
<mailto:newsspea...@gmail.com>> wrote:
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
<amadva...@gmail.com <mailto:amadva...@gmail.com>> wrote:
On Mon, Nov 30, 2020 at 12:27 PM Warin <61sundow...@gmail.com
<mailto:61sundow...@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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