[Talk-GB] Offsets between OS and OSM data (was Building with mapseg)

[Tim François]

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_osm at yahoo.co.uk> wrote:

From: Jerry Clough - OSM <sk53_osm at yahoo.co.uk>
Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg)
To: talk-gb at 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 <sk1ppy14 at yahoo.co.uk>
To: Talk-GB at openstreetmap.org; Chris Hill <osm at 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 <osm at raggedred.net> wrote:

From: Chris Hill <osm at raggedred.net>
Subject: Re: [Talk-GB] Offsets between OS and OSM data (was Building with mapseg)
To: Talk-GB at 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 <sk1ppy14 at yahoo.co.uk 
> <mailto:sk1ppy14 at 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-GB at openstreetmap.org <mailto:Talk-GB at openstreetmap.org>
>     http://lists.openstreetmap.org/listinfo/talk-gb
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Talk-GB mailing list
> Talk-GB at openstreetmap.org
> http://lists.openstreetmap.org/listinfo/talk-gb
>   


_______________________________________________
Talk-GB mailing list
Talk-GB at openstreetmap.org
http://lists.openstreetmap.org/listinfo/talk-gb





       





      
-----Inline Attachment Follows-----

_______________________________________________
Talk-GB mailing list
Talk-GB at openstreetmap.org
http://lists.openstreetmap.org/listinfo/talk-gb



      
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk-gb/attachments/20100530/7f9156c8/attachment-0001.html>