Re: Good practice for publishing geometry of a thing as different geometry types?

Hello Josh,

It could be possible to add more context to the geometries, to express that
they are a footprint or a centroid for instance. But I think that extra
context will not be crucial for many use cases. Especially since there is
no standard vocabulary for that extra meaning yet  (although the vocabulary
I try to use does have a centroid property: http://data.ign.fr/def/geometrie
#centroid).

But I suspect at the heart of your comments is the question what a geometry
really is. There are at least two possible definitions:
A) The geometry of a thing is its real world shape.
B) The geometry of a thing is a model of its real world shape.

I think I silently use definition B. But if others assume definition A that
could lead to problems. I am ashamed to have to admit that I don't know the
official OGC party line in this case. But it would be great if an updated
GeoSPARQL standard could have a direct link to a core definition of
geometry.

As for your last example (two coordinate strings that differ in their CRS)
in my line of thinking (adherent of definition B) that would be modelled as
separate geometries. An extended example:

ex:location1234
   a dcterms:Location ;
   locn:geometry ex:geom1234_1, ex:geom1234_2, ex:geom1234_3, ex_geom1234_4
;

ex:geom1234_1
   a geom:Geometry, locn:Geometry, geom:Point ;
   locn:location ex:location123 ;
   geom:crs <http://www.opengis.net/def/crs/EPSG/0/28992> ;
   geosparql:asWKT "<http://www.opengis.net/def/crs/EPSG/0/28992>
POINT(...)"^^geosparql:wktLiteral .

ex:geom1234_2
   a geom:Geometry, locn:Geometry, geom:Polygon ;
   locn:location ex:location123 ;
   geom:crs <http://www.opengis.net/def/crs/EPSG/0/28992> ;
   geosparql:asWKT "<http://www.opengis.net/def/crs/EPSG/0/28992>
POLYGON(...)"^^geosparql:wktLiteral .

ex:geom1234_3
   a geom:Geometry, locn:Geometry, geom:Point ;
   locn:location ex:location123 ;
   geom:crs <http://www.opengis.net/def/crs/OGC/1.3/CRS84> ;
   geosparql:asWKT "POINT(...)"^^geosparql:wktLiteral .

ex:geom1234_4
   a geom:Geometry, locn:Geometry, geom:Polygon ;
   locn:location ex:location123 ;
   geom:crs <http://www.opengis.net/def/crs/OGC/1.3/CRS84> ;
   geosparql:asWKT "POLYGON(...)"^^geosparql:wktLiteral .


Note that I also included a backlink from geometry to location (locn
:location).

The question still is: can this be considered a good practice, given
currently available standards/vocabularies?

Regards,
Frans






2016-05-04 19:10 GMT+02:00 Joshua Lieberman <jlieberman@tumblingwalls.com>:

> Do you mean:
>
>
> ex:location1234
>    a dcterms:Location, ex:feature ;
>    ex:centroid ex:geom1234 ;
>    ex:footprint ex:geom6789 .
>
> ex:geom1234
>    a geom:Geometry, gsp:Point ;
>    geom:crs <http://www.opengis.net/def/crs/EPSG/0/28992> ;
>    gsp:asWKT "<http://www.opengis.net/def/crs/EPSG/0/28992>
> POINT(...)"^^geosparql:wktLiteral .
>
> ex:geom6789
>    a geom:Geometry, gsp:Polygon ;
>    geom:crs <http://www.opengis.net/def/crs/EPSG/0/28992> ;
>    gsp:asWKT "<http://www.opengis.net/def/crs/EPSG/0/28992>
> POLYGON(...)"^^geosparql:wktLiteral .
>
>
> In that case, the range of gsp:asWKT is not a geometry, but a set of
> coordinate positions locating the geometry, so “POLYGON” is the format of
> the coordinate string, not the geometry class per se.
>
>
> The coordinate information is more problematic, since one could easily
> want to have
>
> ex:geom6789
>    a geom:Geometry, gsp:Polygon ;
>    geom:crs <http://www.opengis.net/def/crs/EPSG/0/28992> ;
>    gsp:asWKT "<http://www.opengis.net/def/crs/EPSG/0/28992>
> POLYGON(...)"^^geosparql:wktLiteral .
>
>    gsp:asWKT "POLYGON(...)"^^geosparql:wktLiteral .
>
>     gap:asGML “…”
>
> I consider asWKT to be problematic for this reason, and one ground for
> updating the GeoSPARQL standard.
>
>
>  Josh
>
>