Sooooo... I take that to mean that I should really be using the correct *.prj file, rather than gdal's inbuilt datum?
Tim --- On Sun, 30/5/10, Jerry Clough - OSM <sk53_...@yahoo.co.uk> wrote: From: Jerry Clough - OSM <sk53_...@yahoo.co.uk> Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg) To: talk-gb@openstreetmap.org Date: Sunday, 30 May, 2010, 12:30 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 <sk1pp...@yahoo.co.uk> To: Talk-GB@openstreetmap.org; Chris Hill <o...@raggedred.net> 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 <o...@raggedred.net> wrote: From: Chris Hill <o...@raggedred.net> Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg) To: Talk-GB@openstreetmap.org 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 <sk1pp...@yahoo.co.uk > <mailto:sk1pp...@yahoo.co.uk>> 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 > talk...@openstreetmap.org <mailto: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 > _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb -----Inline Attachment Follows----- _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
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