<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Sooooo... I take that to mean that I should really be using the correct *.prj file, rather than gdal's inbuilt datum?<br><br>Tim<br><br>--- On <b>Sun, 30/5/10, Jerry Clough - OSM <i><sk53_osm@yahoo.co.uk></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: Jerry Clough - OSM <sk53_osm@yahoo.co.uk><br>Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg)<br>To: talk-gb@openstreetmap.org<br>Date: Sunday, 30 May, 2010, 12:30<br><br><div id="yiv975976894"><style type="text/css"><!--#yiv975976894 DIV {margin:0px;}--></style><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">Hi Tim,<br><br>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.<br><br>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 <a rel="nofollow" target="_blank" href="http://www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/guide6.html">OS Coordinate Systems Guide</a>.<br><br>Jerry<br><br>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.<br><div><br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font size="2" face="Tahoma"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Tim François <sk1ppy14@yahoo.co.uk><br><b><span style="font-weight: bold;">To:</span></b> Talk-GB@openstreetmap.org; Chris Hill <osm@raggedred.net><br><b><span style="font-weight: bold;">Sent:</span></b> Sun, 30 May, 2010 12:16:33<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg)<br></font><br><table border="0" cellpadding="0" cellspacing="0"><tbody><tr><td style="font: inherit;" valign="top">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?<br><br>Tim<br><br>--- On <b>Sun, 30/5/10, Chris Hill <i><osm@raggedred.net></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: Chris Hill <osm@raggedred.net><br>Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg)<br>To: Talk-GB@openstreetmap.org<br>Date: Sunday, 30 May, 2010, 11:53<br><br><div class="plainMail">I believe the StreetView tiles are offset south(ish) by a few metres in <br>East Yorkshire too. Reprojected shape files line up well with surveyed <br>data. I have traced a few buildings from StreetView but I've stopped <br>until I had worked out what was
wrong. Now given other people's comments <br>I do think there may be some discrepancy.<br><br>Would a few carefully surveyed road junctions with many GPS traces to <br>work from help to identify any discrepancy? Or is there a better way?<br><br>Cheers, Chris<br><br>Kevin Peat wrote:<br>> I'm in Devon and I see the same thing although whether it is just the <br>> SW I don't know. <br>><br>> The Streetview tiles (as I see them in JOSM) are all offset to the SE <br>> by 5-10 metres. I've converted some woods in my area from the <br>> VectorDistrict data using this process,<br>><br>> <a rel="nofollow" target="_blank" href="http://wiki.openstreetmap.org/wiki/Using_OS_Shapefiles">http://wiki.openstreetmap.org/wiki/Using_OS_Shapefiles</a><br>><br>> and the converted data looks good to me compared to my previous <br>> surveys but comes out different to the tiles, so I'm thinking that the <br>> tiles are
wrong.<br>><br>> Kevin<br>><br>><br>><br>><br>> On 30 May 2010 09:08, Tim François <<a rel="nofollow">sk1ppy14@yahoo.co.uk</a> <br>> <mailto:<a rel="nofollow">sk1ppy14@yahoo.co.uk</a>>> wrote:<br>><br>> > On a side note, has anybody noticed a consistent tendency<br>> > for existing<br>> > independently surveyed roads to be offset northwards (by<br>> > around 5-10<br>> > metres) from the OS data (vectormap and streetview)? I've<br>> > seen various<br>> > cases of existing roads being edited to be consistent with<br>> > OS data,<br>>
> but I'm not convinced this is a good idea since the problem<br>> > seems to<br>> > be consistent in one direction.<br>><br>> Glad I'm not the only one. Here in the SW I see the same offsets,<br>> although I find the VectorDistrict data to be more like the GPS<br>> surveyed data. This means that the StreetView tiles do not match<br>> up with the VectorDistrict either: I've been importing some rivers<br>> and reservoirs from the VectorDistrict data (namely the River Chew<br>> and Chew Valley Lake) and I've found that the polygons seem to be<br>> shifted compared to the equivalent positions in StreetView by<br>> about 10 metres.<br>><br>>
I guess this is an expected artifact of the reprojection methods?<br>><br>> Tim<br>><br>><br>><br>><br>> _______________________________________________<br>> Talk-GB mailing list<br>> <a rel="nofollow">Talk-GB@openstreetmap.org</a> <mailto:<a rel="nofollow">Talk-GB@openstreetmap.org</a>><br>> <a rel="nofollow" target="_blank" href="http://lists.openstreetmap.org/listinfo/talk-gb">http://lists.openstreetmap.org/listinfo/talk-gb</a><br>><br>><br>> ------------------------------------------------------------------------<br>><br>> _______________________________________________<br>> Talk-GB mailing list<br>> <a rel="nofollow">Talk-GB@openstreetmap.org</a><br>> <a rel="nofollow" target="_blank"
href="http://lists.openstreetmap.org/listinfo/talk-gb">http://lists.openstreetmap.org/listinfo/talk-gb</a><br>> <br><br><br>_______________________________________________<br>Talk-GB mailing list<br><a rel="nofollow">Talk-GB@openstreetmap.org</a><br><a rel="nofollow" target="_blank" href="http://lists.openstreetmap.org/listinfo/talk-gb">http://lists.openstreetmap.org/listinfo/talk-gb</a><br></div></blockquote></td></tr></tbody></table><br>
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