Tim, What's the scan file size? Will happily help look at calibration as I'm doing it all the time for the 1:25k so set up to do it easily. If I know the file size I can try a similar size on my box here.
How many calibration points are you needing per sheet to do a reasonable job? Cheers Andy >-----Original Message----- >From: talk-gb-boun...@openstreetmap.org [mailto:talk-gb- >boun...@openstreetmap.org] On Behalf Of TimSC >Sent: 18 October 2009 4:11 PM >To: talk-gb@openstreetmap.org >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 > >The best way of determining the error in rectification is to get the lat >lon of a grid square corner. stick that into the OSTN02 transformation >(http://gps.ordnancesurvey.co.uk/convert.asp). The true corner position >can be found by rounding the resultant grid coordinates to the nearest >thousand. (Assuming the error is less than 500m!) Rectification errors >seem to be in the order of 0 to 20m depending on the area. If any areas >have errors that exceed this, let me know and I will investigate it. > >The next steps are to rectify the other sheets we have scanned. >http://wiki.openstreetmap.org/wiki/7th_Series > >Is there anyone who can help us with sheet calibration? Having a linux >box with a decent amount of RAM is a requirement. If yes, get in touch >with me and Steve Chilton. > >Tim > > >_______________________________________________ >Talk-GB mailing list >Talk-GB@openstreetmap.org >http://lists.openstreetmap.org/listinfo/talk-gb _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
