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Re: Good practice for RDF publishing of multiple geometries with different CRSs?

From: Andrea Perego <andrea.perego@jrc.ec.europa.eu>
Date: Mon, 11 Apr 2016 17:50:04 +0200
To: Frans Knibbe <frans.knibbe@geodan.nl>
Cc: matthew.perry@oracle.com, Raphaël Troncy <raphael.troncy@eurecom.fr>, SDW WG Public List <public-sdw-wg@w3.org>
Message-id: <570BC7AC.5010008@jrc.ec.europa.eu>
On 11/04/2016 12:21, Frans Knibbe wrote:
> Hello Matt, Raphaël,
>
> Thank you for your answers! It is nice to see that Matt's first solution
> aligns with Raphaël's solution. The GeoSPARQL query will work, but I
> think it is a less general solution, it depends on a particular API
> (SPARQL) and support of a particular function (getSRID) by the SPARQL
> engine.
>
> It's also nice to see Matt signalling the need for standardization and
> Raphaël providing some or all of it next. I do notice a difference in
> approach: In Matt's example a set of coordinates using a particular CRS
> is a serialization of a geometry, while in Raphaël's example it is the
> geometry itself. Is any of these two approaches based on core semantics
> of geometry (e.g. the OGC simple features model)? It seems important
> that we use the same definitions in this group.

I think it's worth mentioning the (long) discussion on this topic we had 
in the LOCADD CG.

I'm copy-pasting below the relevant part of the summary [1]:

[[
The possibility of specifying a CRS separately from the geometry 
representation / serialisation was supported by two main use cases:

1. Ability to explicitly specify a CRS in data aggregated from different 
sources, which are using, implicitly, different default CRSs - see 
Raphaël's mail (22 Dec 2013)

2. Ability to query the CRS (e.g., filter geometries based on their CRS) 
also in SPARQL endpoints not supporting GeoSPARQL or stSPARQL - see 
Frans's mail (30 Dec 2013)

The discussion basically focussed on two main issues:

- The possible drawbacks of specifying the CRS separately from the 
geometry representation.

- Whether it would be possible or not to address the use cases with CRS 
specified as part of the geometry representation / serialisation.

The group moved towards the agreement to allow both approaches as 
alternative and not exclusive options for the specification of a CRS.
]]

Personally, I think the point is still valid.

Andrea

----
[1]https://www.w3.org/community/locadd/wiki/Use_case:_CRS_specification
Received on Monday, 11 April 2016 15:50:46 UTC

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