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

[Tim François]

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
>
>
>
>
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