[Talk-GB] OSM UK's first tile layer

[James Derrick]

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
     lists at 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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