[Talk-GB] OS open map local polygon accuracy

[Philip Barnes]

On Mon, 2016-06-06 at 18:04 +0100, roger at beardandsandals.co.uk wrote:
> I was thinking more of the woodland polygons, and the linear
> features. They are a lot harder to run a complex feature
> simplification algorithm on than the building outlines.  My test area
> is Warton Crag in north Lancashire. There is a lot of stuff there
> that looks like it has been hand traced from OS open street view
> rasters, which I suspect have been translated to WGS84 without using
> the OSTN02 data.

Past experience of OS Opendata Woodland imports has left me feeling
that they need to be checked very thoroughly before we consider using
them. Large areas that have never been woodland had been imported as
woodland and I have had to spend a lot of time cleaning up these
imports, there are also the strange gaps which had been imported and do
not exist in real life.

Personally I would just stick to tracing woodland from bing/mapbox
imagery.

Phil (trigpoint)

> Roger
> On 6 Jun 2016 5:35 pm, Ed Loach <edloach at gmail.com> wrote:
> The shapes themselves aren’t particularly accurate, if you look at
> say building outlines and compare to Bing. It shouldn’t take long to
> find a non-rectangular building on Bing which has been approximated
> to rectangular in OS Open Map Local
>  
> Ed
>  
> From: roger at beardandsandals.co.uk [mailto:roger at beardandsandals.co.uk
> ] 
> Sent: 06 June 2016 14:45
> To: talk-gb at openstreetmap.org
> Subject: [Talk-GB] OS open map local polygon accuracy
>  
> Hi,
> I have been looking at the OS openmap local vector dataset. I noticed
> that the coordinates in there are centimetre level accuracy. I am
> speculating how the OS made this dataset a "nominal viewing scale"
> of  1:10000. Scales are somewhat irrelevant to vector data. Have they
> degraded the geometry points by thinning or averaging, or is the data
> still at survey level accuracy? I have some old (paid for) OS master
> map data. It would be interesting to compare the polygons in there
> with the the openmap local ones. But before I search my loft for the
> disc, has anyone already done this?
> Roger
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