Hi Tim, Yes there is, at least with the version of GDAL I use. Chillly has written about this on his blog, and the changes needed (adding Helmert transformations - -sound fancy doesn't it) to the standard projection are noted in previous messages here in talk-gb.
I think the divergence is much greater on the E of the country: probably why Chilly and I worried most about it. Even with these the accuracy compared with the OSGB02 will be upto 5 metres out. See OS Coordinate Systems Guide. Jerry PS. StreetView and OSM seem to match up quite well for Nottingham. I've just rendered a set of tiles in OSGB36 of the same scale and boundaries as StreetView which at least removes some of the projection transformation artefacts. ________________________________ From: Tim François <[email protected]> To: [email protected]; Chris Hill <[email protected]> Sent: Sun, 30 May, 2010 12:16:33 Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg) By the way, which method are people using to re-project the VectorDistrict data? I'm using the inbuilt datum in gdal - is anyone using the correct *.prj file, and is there a difference? Tim --- On Sun, 30/5/10, Chris Hill <[email protected]> wrote: >From: Chris Hill <[email protected]> >Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with >mapseg) >To: [email protected] >Date: Sunday, 30 May, 2010, 11:53 > > >I believe the StreetView tiles are offset south(ish) by a few metres in >East Yorkshire too. Reprojected shape files line up well with surveyed >data. I have traced a few buildings from StreetView but I've stopped >until I had worked out what was > wrong. Now given other people's comments >I do think there may be some discrepancy. > >Would a few carefully surveyed road junctions with many GPS traces to >work from help to identify any discrepancy? Or is there a better way? > >Cheers, Chris > >Kevin Peat wrote: >> I'm in Devon and I see the same thing although whether it is just the >> SW I don't know. >> >> The Streetview tiles (as I see them in JOSM) are all offset to the SE >> by 5-10 metres. I've converted some woods in my area from the >> VectorDistrict data using this process, >> >> http://wiki.openstreetmap.org/wiki/Using_OS_Shapefiles >> >> and the converted data looks good to me compared to my previous >> surveys but comes out different to the tiles, so I'm thinking that the >> tiles are > wrong. >> >> Kevin >> >> >> >> >> On 30 May 2010 09:08, Tim François <[email protected] >> <mailto:[email protected]>> wrote: >> >> > On a side note, has anybody noticed a consistent tendency >> > for existing >> > independently surveyed roads to be offset northwards (by >> > around 5-10 >> > metres) from the OS data (vectormap and streetview)? I've >> > seen various >> > cases of existing roads being edited to be consistent with >> > OS data, >> > > but I'm not convinced this is a good idea since the problem >> > seems to >> > be consistent in one direction. >> >> Glad I'm not the only one. Here in the SW I see the same offsets, >> although I find the VectorDistrict data to be more like the GPS >> surveyed data. This means that the StreetView tiles do not match >> up with the VectorDistrict either: I've been importing some rivers >> and reservoirs from the VectorDistrict data (namely the River Chew >> and Chew Valley Lake) and I've found that the polygons seem to be >> shifted compared to the equivalent positions in StreetView by >> about 10 metres. >> >> > I guess this is an expected artifact of the reprojection methods? >> >> Tim >> >> >> >> >> _______________________________________________ >> Talk-GB mailing list >> [email protected] <mailto:[email protected]> >> http://lists.openstreetmap.org/listinfo/talk-gb >> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> 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 >
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