[Talk-GB] OS 7th series, accuracy update, request for calibration help

[Jerry Clough - OSM]

I wouldn't be surprised if Kintyre other than NR71 & NR72 (Campbeltown) is derived from much earlier mapping. Those two octads are the only ones published for Kintyre in the 25k provisional/first series. Certainly for other parts of highland Scotland serious errors existed until the 50k 2nd series (one reason why this appeared for the Highlands first). If I'm right there may also be errors on Arran, which also only had 2 10km squares published. On the other hand, Arran may have been much better surveyed in the 19th century because of its geological interest.

Jerry Clough
SK53




________________________________
From: TimSC <mapping at sheerman-chase.org.uk>
To: talk-gb at openstreetmap.org
Sent: Sunday, 18 October, 2009 16:11:08
Subject: [Talk-GB] OS 7th series, accuracy update, request for calibration help

Hi all,

I have updated the 7th series layer with improved accuracy. It seems as 
if the Helmert approximation of the OS grid reference to WGS84 was not 
accurate enough; I was getting transform errors of approximately 20m. 
Also, to my surprise the next biggest error seems to be surveying 
errors. For example, see around the Mull of Kintyre where the survey 
errors are around 40m (near NR730100).

http://www.openstreetmap.org/?lat=55.3339&lon=-5.5737&zoom=14&layers=B000FTF

..snip

Tim


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