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Re: Geo in RDF (was Re: Censorship?)

From: Stuart Williams <skw@epimorphics.com>
Date: Tue, 09 Nov 2010 11:58:15 +0000
Message-ID: <4CD93757.1070508@epimorphics.com>
To: William Waites <ww@styx.org>
CC: Gannon Dick <gannon_dick@yahoo.com>, Leigh Dodds <leigh.dodds@talis.com>, Mike Norton <xsideofparadise@yahoo.com>, W3C e-Gov IG <public-egov-ig@w3.org>
Opps... forgot the references:

[1] http://www.w3.org/2005/Incubator/geo/XGR-geo/#owl
[2] http://www.w3.org/2005/Incubator/geo/XGR-geo/W3C_XGR_Geo_files/geo_2007.owl
[3] http://www.georss.org/gml

On 09/11/2010 11:50, Stuart Williams wrote:
> Hello William,
>
> On 08/11/2010 23:48, William Waites wrote:
>> On Mon, Nov 08, 2010 at 03:28:12PM -0800, Gannon Dick wrote:
>>>
>>> Latitude and Longitude are a complete coordinate system - the
>>> ordering is a continuous function.  Entity Names and
>>> Vocabulary Encoding Schemes form a complete set, something a
>>> bit different.
>>
>> If I understand correctly, you see a problem with RDF where
>> there is no standard way to express things other than points?
>> Such as lines, polygons, polygons with holes, multipolygons,
>> geometry collections, the whole suite of shapes that GIS
>> systems normally deal with?
>>
>> If so I think you are partially right. As far as I know there
>> has been little work done in modelling these sorts of things
>> in RDF, and I think the triplestores that have even very basic
>> support for geodata (e.g. points) only support the simplest
>> of operations with them (e.g. bounding box or radius search).
>>
>> That said there's no reason you couldn't express more complex
>> shapes in RDF. The process would be fairly mechanical (e.g.
>> straightforward translation of WKT, KML or whatever) this
>> is already a very well understood area.
> Though they may fall short of being 'standards' at the moment, you might be 
> interested in the vocabulary at [1,2] if you haven't already come across it. 
> It picks up LineString, LinearRing, Envelope (i.e. bounding box) and Polygon 
> from GeoRSS[3] and AFAICT with care gives an RDF/XML reading of a a piece foe 
> GeoRSS/XML syntax. It also provides linkage to non-WGS84 coordinate reference 
> systems.
>
> I'm also aware of an approach that adds a GML/XML expression as an XMLLiteral 
> to an RDF node representing the geometric extent of some feature  an :asGML 
> property e.g.:
>
> @prefix geometry: <http://data.ordnancesurvey.co.uk/ontology/geometry/> .
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
>
> <http://data.ordnancesurvey.co.uk/id/7000000000025559>
>         skos:prefLabel    "The District of South Gloucestershire";
>         geometry:extent <http://data.ordnancesurvey.co.uk/doc/geometry/71548>;
>         ... ;
>         .
>
> <http://data.ordnancesurvey.co.uk/id/geometry/71548>
>         rdf:type geometry:AbstractGeometry ;
>         geometry:hectares "53664.694"
>         geometry:asGML  "<gml:Polygon xmlns:gml=\"http://www.opengis.net/gml\ 
> "srsName=\"os:BNG\"><gml:exterior><gml:LinearRing><gml:posList 
> srsDimension=\"2\">356578.2 193831.7 356573.4 193822.9 356529.9 193733.7 
> 356510 .3 193690.2 356495.1 193661.9...  356578.2 193831.7 
> </gml:posList></gml:LinearRing></gml:exterior></gml:Polygon>"^^rdf:XMLLiteral .
>
> This is work from John Goodwin at Ordnance Survey. At present I don't think 
> the :asGML triples have been published, but I believe that they are coming 
> (soon).
>
>> By far the easiest way to deal with it is just to put WKT
>> into, e.g. dc:spatial (maybe we need a WKT datatype) and
>> use any GIS system you like to do the actual indexing. Maybe
>> add some built-in functions to a SPARQL engine to help with
>> querying...
>
> A widely adopted, ideally single, common practice would be nice!
>
>> Or have I misunderstood completely?
>>
>> And what does this have to do with censorship?
>>
>> Cheers,
>> -w
>>
> BR
>
> Stuart


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Received on Tuesday, 9 November 2010 12:11:36 GMT

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