Richard Fairhurst wrote: >Sent: 07 October 2009 5:34 PM >To: [email protected] >Subject: Re: [Talk-GB] OS 7th Series offset > >> > I get a much better alignment for that area with the re-rectified >> NPE tiles >> > from TimSC's space at http://dev.openstreetmap.org/~timsc/wms2/map.php? >> Yes, indeed, vastly better (and the images are clearer too, and the >> tiles braking up problem isn't there). Even if I pan several tens of >> km it is still in sync, and it seems to be in sync from the download >> - no initial adjustment needed. > > >I rectified the NPE images available in Potlatch (and later >republished via Tim's WMS for those of you using inferior editors ;) ) >with 90 control points per sheet. It took bloody ages! But it does >mean they're very, very close to the originals. > >The original NPE images found at www.npemap.org.uk, and on the older >WMS, had only been rectified with some rough whole-sheet rotation and >shearing operations in Photoshop or similar. These were in fact >rectified for postcode input at npemap.org.uk, where the accuracy was >less critical. > >Personally I'm a bit tired of fixing JOSM users' crappy tracings and >would like the old WMS to be removed! > >But the fact that even the Potlatch 90-point NPE tiles need a little >manual correction to GPS (space-drag in Potlatch) tells you something >about the OS's surveying accuracy back then. As the 7th series >followed straight on from NPE with no major resurvey at first, you >should expect there still to be some displacement. >
No how about I ask the OS under a FOIA request to provide the error correction values (rotation and position) for each of my 1:25k sheets. I just wonder if they would play ball. I'll send one in once the current one is back. Don't wish to taunt them too much :-) Cheers Andy >cheers >Richard > >_______________________________________________ >Talk-GB mailing list >[email protected] >http://lists.openstreetmap.org/listinfo/talk-gb _______________________________________________ Talk-GB mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-gb
