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

>
> But I suspect at the heart of your comments is the question what a
> geometry really is. There are at least two possibledefinitions:
> 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 agree: in practice, (B) is always the case.  No representation of
geometry will be completely accurate, and different levels of approximation
(different models) are appropriate in different contexts.



On 9 May 2016 at 15:35, Frans Knibbe <frans.knibbe@geodan.nl> wrote:

> 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
>>
>>
>