RE: SpatialThing and feature (again)

> I remember @danbri saying not to get too hung up of W3C Basic Geo as there wasn't a lot of thought that went into it ...

Yes, I've seen that too.
I'd also remind folk of OWA.

________________________________
From: Jeremy Tandy <jeremy.tandy@gmail.com>
Sent: Friday, 21 April 2017 4:42:46 PM
To: Joshua Lieberman
Cc: Cox, Simon (L&W, Clayton); Rob Atkinson; harth@kit.edu; public-sdw-wg@w3.org
Subject: Re: SpatialThing and feature (again)

Noted. I think that we should express it like this - but note the ambiguity in definition.

I remember @danbri saying not to get too hung up of W3C Basic Geo as there wasn't a lot of thought that went into it ...
On Fri, 21 Apr 2017 at 17:40, Joshua Lieberman <jlieberman@tumblingwalls.com<mailto:jlieberman@tumblingwalls.com>> wrote:
Jeremy,

A pretty good summary. One might interpret the W3C Basic Geo properties as mapping to a geometry property (as GeoRSS Simple does), but there isn’t conclusive evidence that this was originally intended.

Josh

On Apr 21, 2017, at 11:33 AM, Jeremy Tandy <jeremy.tandy@gmail.com<mailto:jeremy.tandy@gmail.com>> wrote:

Hi all-

I've spent more than a few minutes parsing through the email chain.

1/ Clemens' summary (from mid way though) suggests that (a) ISO 19109 Feature is [also] a geosparql:Feature, (b) these may or may not have attached geometry properties
2/ Andrea suggests that "only [those] ISO 19109 Features [with spatial extent] are Spatial Things according to the BP definition" - but Josh suggests we're using "spatial extent" as a shorthand for "real-world phenomena", and that "making the connection [between abstraction and real-world thing] formal and explicit is not necessary for Web purposes"

So I'm seeing that there's no inconsistency to explain away.

Please confirm that I've read this OK. Apologies if I've missed the point!

And, talking of Points ... I see that there is potential for confusion regarding the "Feature/Geometry amalgam".

We could insert a "green note" into the BP document identifying the potential for inconsistency - as defined in Andreas' example:

> Because a w3cgeo:SpatialThing has lat/lon, some people might equate a w3cgeo:SpatialThing with a geosparql:Geometry.
>
> Because the w3cgeo:SpatialThing is an instance of foaf:Person, some other people find it natural to equate the w3cgeo:SpatialThing with a geosparql:Feature.
>
> Based on data from different source we now have an inconsistency, because the w3cgeo:SpatialThing is an instance of both geosparql:Feature and geosparql:Geometry, which are defined as disjoint.

... and reaffirm that _we_ see Feature (SpatialThing) as disjoint from geometry, but that this might be at odds with some people's interpretations. As Josh says: "we can’t really say there is a mapping from W3C Basic Geo to/from anything based on 19109."

Am I summarising correctly?

Thanks, Jeremy


On Fri, 21 Apr 2017 at 15:33 Joshua Lieberman <jlieberman@tumblingwalls.com<mailto:jlieberman@tumblingwalls.com>> wrote:
Ah, I had thought that the domains of geo:lat and geo:lon were geo:Point, since that is what is generally referred to in narrative. If a resource carrying the lat/lon properties implies that it is a SpatialThing, not only the Point subclass, adding the properties doesn’t resolve any feature / geometry ambiguity. Your equivalences are certainly possible, but geosparql doesn’t / shouldn’t support adding direct positions to features, so entailing something with geo:lat and geo:lon as geosparql:SpatialObject rather than geosparql:Geometry doesn’t really work. And if we can’t derive that use of geo:lat and geo:lon imply both a feature and a geometry, than Andrea is correct that we can’t really say there is a mapping from W3C Basic Geo to/from anything based on 19109. That may be unfortunate.

—Josh

On Apr 20, 2017, at 8:38 PM, simon.cox@csiro.au<mailto:simon.cox@csiro.au> wrote:

Hold on a moment folk – does this problem really exist?

I’m looking at http://www.w3.org/2003/01/geo/wgs84_pos# which is the RDF/XML serialization of W3C Basic Geo.
Here’s the key axioms.

geo:lat   rdfs:domain geo:SpatialThing .
geo:long rdfs:domain geo:SpatialThing .
geo:Point rdfs:subClassOf geo:SpatialThing .

And from http://schemas.opengis.net/geosparql/1.0/geosparql_vocab_all.rdf
since

geosparql:Geometry rdfs:subClassOf geosparql:SpatialObject .

then it looks to me like

geo:SpatialThing owl:equivalentClass geosparql:SpatialObject .
geo:Point rdfs:subClassOf geosparql:Geometry .

and there is no inconsistency. Appearance of geo:lat and geo:long properties only entails that it is a geosparql:SpatialObject, so can be either a Feature or a Geometry.

Am I missing something?

Simon

From: Rob Atkinson [mailto:rob@metalinkage.com.au]
Sent: Thursday, 20 April, 2017 06:24
To: Joshua Lieberman <jlieberman@tumblingwalls.com<mailto:jlieberman@tumblingwalls.com>>; Andreas Harth <harth@kit.edu<mailto:harth@kit.edu>>
Cc: public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>
Subject: Re: SpatialThing and feature (again)


This could also be resolved by thinking of geo:long as a property that can entail a geometry property of the feature - maybe its even a geometry property in the same way that a 2D point is a partial representation of a 3D location?

Rob

On Thu, 20 Apr 2017 at 02:38 Joshua Lieberman <jlieberman@tumblingwalls.com<mailto:jlieberman@tumblingwalls.com>> wrote:
Andreas,

It may not be worth delving too deeply into this...

W3C Basic Geo defines SpatialThing and then subclasses it to Point carrying the lat and long properties. No one defines their own SpatialThings, they simply add geo:lat and geo:long properties to some resource X to turn it into “also a Point”, in other words “also a geometry”. This implies for most users but does not actually assert that resource X is both a feature and a geometry. One could form a subclass of geo:SpatialThing that was actually disjoint with geo:Point or other geometry,  which would then align more-or-less with iso geosparql:Feature, hence the assertion that some geo:SpatialThings are geosparql:Features. This is largely hypothetical.

There is a similar property in GeoRSS, the point(pos) property, but this doesn’t try to create one feature-geometry amalgam. It’s simply a shortcut for a longer expression that identifies some resource as a _Feature with a “where" object property connecting to a Point geometry resource.

It might be most accurate to say that your example of using W3C Basic Geo to represent feature and geometry in the “style” of geosparql is actually the longhand of what people are trying to do when they do use geo:lat and geo:long, identifying a resource as a real world feature and giving it a closely allied point geometry.

—Josh

> On Apr 19, 2017, at 11:54 AM, Andreas Harth <harth@kit.edu<mailto:harth@kit.edu>> wrote:
>
> Hi,
>
> On 04/19/17 13:29, Joshua Lieberman wrote:
>> My understanding based on the limited documentation is that w3cgeo:SpatialThing covers both features and models such as geometries, so
>
> that's my understanding too.  With the W3C WGS84 vocabulary you can write:
>
> @prefix geo: <http://www.w3.org/2003/01/geo/wgs84_pos#<http://www.w3.org/2003/01/geo/wgs84_pos>> .
> @prefix : <#> .
>
> :bob a geo:SpatialThing ; geo:lat "52.5196143" ; geo:long "13.4065603" .
>
> So the resource with the URI :bob is both the "feature" and the "geometry".
>
> In other representations (NeoGeo, GeoSPARQL), you would identify two separate
> resources:
>
> @prefix geo: <http://www.w3.org/2003/01/geo/wgs84_pos#<http://www.w3.org/2003/01/geo/wgs84_pos>> .
> @prefix : <#> .
>
> :bob a :Feature ; :geometry _:bnode .
> _:bnode a :Geometry , geo:Point ; geo:lat "52.5196143" ; geo:long "13.4065603" .
>
> The URI :bob now represents the "feature" resource, and the blank node _:bnode
> represents the "geometry" resource.
>
> I wouldn't know how to write OWL axioms to map the two modeling choices though.
>
> Best regards,
> Andreas.
>
>