Re: Some thoughts on http://www.w3.org/TR/sdw-bp/

Hi Peter. Thanks for both positive comments and useful critique. These will
be easy to incorporate in the next working draft in about 6-weeks time -
we've just frozen the draft so we can vote on Monday whether to release the
current version (we like regular releases!)

Jeremy
On Thu, 16 Mar 2017 at 21:14, Ed Parsons <eparsons@google.com> wrote:

> Hi Peter,
>
> You make a very good point about precision, but the examples are actually
> what you are returned... I'm not sure we want to get into questions of
> precision for the intended audience who are generally looking to express a
> location globally within a few metres...
>
> Of course this leads us nicely into the discussion of samePlace as....
>
> Ed
>
>
> On Thu, 16 Mar 2017 at 12:54 Peter Parslow <Peter.Parslow@os.uk> wrote:
>
> Hi all,
> This is becoming a really useful resource - as an introduction to the
> subject area, as well as a set of best practices. Sorry to have not been
> more involved.
>
> I've been reading it again (along with other related articles), prior to
> attending next week's meeting, and a few things come to mind which could
> become improvements.
>
> 1. URI for Eddystone Lighthouse. It is of course fine to use a URI from
> Deutsche Nationalbibliothek, and a URL from Wikidata, if only to
> demonstrate that many URIs can identify the same spatial thing. But I think
> it would be good to honour the actual owners/operators of the lighthouse by
> using their reference:
> https://www.trinityhouse.co.uk/lighthouses-and-lightvessels/eddystone-lighthouse
>
> 2. in section 8 about CRS, it says that lat & long "can express a location
> to within a few metres". In fact there's nothing to stop a lat/long being
> as precise as you like, and I often find ones which are more precise than
> their accuracy should support. By which I mean that quite a lot of software
> defaults to serialising real numbers as decimals with six digits after the
> decimal place - which is something like 1cm on the ground. That accuracy
> can only be achieved with professional equipment, but a discussion of
> accuracy & precision may be out of place in this document (at least, at
> this section). But perhaps dropping the 'within a few metres' bit would be
> appropriate..
>
> And in fact, example 3 gives lat/long with seven and 12 decimal places:
> seven is millimetre accuracy; I'd have to Google the name for a unit small
> enough for 12 decimal places of a degree - probably smaller than an atom!
>
> See
> http://gis.stackexchange.com/questions/8650/measuring-accuracy-of-latitude-and-longitude/8674#8674
>
> Can I recommend reducing the number of digits in the examples.
>
> 3. Further on in section 8, I'm not sure that EPSG:4277 is "the UK
> National Grid"; my reading of the EPSG register is that this is the code
> for OSGB36, which is the geodetic reference system on which the project
> British National Grid is based. The code for the British National Grid is
> 27700.
>
> We don't call it "UK" national grid, because Ireland generally uses a
> different one.
>
> That's all for today; I may get time to read a bit more tomorrow.
>
> Peter
>
>
> Peter Parslow
> Principal Geographic Information Architect
> Products & Innovation, Ordnance Survey
>
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>
> *Ed Parsons *FRGS
> Geospatial Technologist, Google
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