Hi,
On 27/10/2020 06:18, Adrian via Talk-GB wrote:
I agree with Rob that the misalignment of 5m is obvious if you look at Hugh
Town (Scilly). Both if you compare with the OSM data and if you compare with
the tracklogs that have been uploaded to OSM. So this transformation won't do.
I think we need to go for the look-up table.
Whilst the details of your geodesy is impressive but way beyond my
expertise, over ten years of OSM survey traces suggests another factor
to be wary of when comparing sub-10m position sources.
Using a Garmin Oregon 550 as a baseline, Oregon 650 and 750 consistently
give location between 4-8m North North West in Northumberland - the tool
may influence the measurement beyond your accuracy.
For resilience, I map with at least two GPSr on my bike handlebars and
regularly upload both tracks to OSM and use both to better position
mapping and any layers such as imagery. Over the years I've used five or
six Garmin GPSr. None are even close to a 'proper' differential total
station, however with datum/ spheroid set to WGS 84, the same tools and
JOSM workflow show the offset. Changing GPS/ GLONASS or WAAS/ EGNOS
seems to have less impact than the choice of Garmin unit (same settings
across devices). Firmware updates have changed motion compensation when
changing direction fast, but the offset remains.
The trouble will be is without device data in tracklogs there's no way
to separate random from systematic offsets (even if you had them...) -
you can only average all data.
Thanks for your interesting work - I remember tales from Registers of
Scotland of an OS baseline survey error that 'moved' the East coast by
many meters proving 'You Are Here' is hard to quantify!
James
--
James Derrick
li...@jamesderrick.org, Cramlington, England
I wouldn't be a volunteer if you paid me...
https://www.openstreetmap.org/user/James%20Derrick
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