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RE: Sub-properties for locn:geometry?

From: <Simon.Cox@csiro.au>
Date: Tue, 21 Jan 2014 21:56:18 +0000
To: <John.Goodwin@ordnancesurvey.co.uk>, <raphael.troncy@eurecom.fr>, <andrea.perego@jrc.ec.europa.eu>, <frans.knibbe@geodan.nl>
CC: <sven.schade@jrc.ec.europa.eu>, <public-locadd@w3.org>
Message-ID: <2A7346E8D9F62D4CA8D78387173A054A5FF68609@exmbx04-cdc.nexus.csiro.au>
John - 

1. 
+1 on 'representative point' over 'centroid'. 
There are many examples of real geographic features which are disconnected multi-polygons or 'gerrymander' shapes where the geometric centroid falls outside the actual geometry. Cartographers have known this for ever, so are used to choosing a representative point that is 'more characteristic' of the feature. (For cities it was traditionally the central Post Office.)

2. 
The locn:extent should be a box, rather than a generic polygon. 
There is nothing in GeoSPARQL SF that corresponds with this. 

In ISO 19107 it is called 'GM_Envelope' for which I made a basic OWL2 implementation here: http://def.seegrid.csiro.au/isotc211/iso19107/2003/geometry#Envelope  

i.e. 
  locn:extent [ a gm:Envelope ] .

However, in ISO 19107 GM_Envelope is not a specialization of GM_Object. 
There are good theoretical reasons for this, but it may be inconsistent with locn:extent rdfs:subClassOf locn:geometry . 

Simon


-----Original Message-----
From: John Goodwin [mailto:John.Goodwin@ordnancesurvey.co.uk] 
Sent: Wednesday, 22 January 2014 6:34 AM
To: RaphaŽl Troncy; Andrea Perego; Frans Knibbe | Geodan
Cc: Sven Schade; LocAdd W3C CG Public Mailing list
Subject: RE: Sub-properties for locn:geometry?

Hi all,

First - thank for the link Raphael - that did make me smile. The problems mixing work and social circles together ;)

Anyway, here is my concrete example starter:

If you look at the OS linked data for 'Southampton':

http://data.ordnancesurvey.co.uk/id/7000000000037256

you will noticed that it is related to a 'Geometry' via the predicate 'extent' and it also has predicates geo:lat, geo:long and 'easting'/'northing'. geo:lat, geo:long and 'easting'/'northing' provide information about a 'representative point' for Southampton (centroid is a bit overloaded I think). This 'representative point' is just a point guaranteed to lie within Southampton. I think it is useful (in this case) to provide both the 'representative point' and the polygon for area Southampton covers. So something like:

os:7000000000037256
  a locn:Location;
  locn:representativePoint os:1234;
  locn:extent os:2458;
  os:1234 a sf:Point;
  os:2468 a sf:Polygon;
  ...  

or if you prefer:

os:7000000000037256
  a locn:Location;
  locn:representativePoint os:1234;
  locn:extent os:2458;
  os:1234 a neogeo:Point;
  os:2468 a neogeo:Polygon;
  ...

Maybe then (in Manchester OWL syntax(ish)):

 locn:representativePoint rdfs:range (neogeo:Point OR sf:Point or geo:Point)  locn:extent rdfs:range (neogeo:Polygon or sf:Polygon)


(not saying representativePoint or extent are best choices for predicate names at this stage).

John


Dr John Goodwin
Principal Scientist
Research,†Ordnance Survey
Adanac Drive, SOUTHAMPTON, United Kingdom, SO16 0AS
Phone: +44 (0) 23 8005 5761
www.ordnancesurvey.co.uk†|†john.goodwin@ordnancesurvey.co.uk Please consider your environmental responsibility before printing this email.


-----Original Message-----
From: RaphaŽl Troncy [mailto:raphael.troncy@eurecom.fr]
Sent: 21 January 2014 15:40
To: Andrea Perego; Frans Knibbe | Geodan
Cc: Sven Schade; LocAdd W3C CG Public Mailing list
Subject: Re: Sub-properties for locn:geometry?

Hello all,

> In order to verify the current position of the group, could you please 
> five your vote to the following proposal:
>
> 1. Definition of sub-properties of locn:geometry to denote MBRs, 
> centroids, etc.
>
> 2. They can be used to specify the MBR, centroid, etc. of a 
> dcterms:Location
>
> 3. They can be used to specify the MDR, centroid, etc. of a geometry

Before we come to a vote (I'm not sure I understand fully those proposals by the way), can we have a *concrete* example (preferably in
turtle) of how we express those things for each of the 3 variants?
As an example, let's pick Southampton or a smaller district (*) of the city.

   RaphaŽl

(*) For example, the district around
https://www.foursquare.com/v/4bc1cd504cdfc9b60b0e9521 :-)

   RaphaŽl

--
RaphaŽl Troncy
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Multimedia Communications Department
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Received on Tuesday, 21 January 2014 21:56:51 UTC

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