[Talk-GB] OS 7th series, accuracy update, request for calibration help
Jerry Clough - OSM
sk53_osm at yahoo.co.uk
Mon Oct 19 10:10:58 BST 2009
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.
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
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).
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