[Geopackage] [SpatiaLite-Users] GeoPackage (GPKG) support in 4.2.0

Even Rouault even.rouault at mines-paris.org
Thu May 22 15:16:04 EDT 2014


Le jeudi 22 mai 2014 09:36:17, Pepijn Van Eeckhoudt a écrit :
> On 22-05-14 00:33, a.furieri at lqt.it wrote:
> > On Thu, 22 May 2014 00:11:06 +0200, Even Rouault wrote:
> >> But... the string GeomCollection appears at a few occurrences in the
> >> GeoPackage specification, so CC'ing the GeoPackage list so that they
> >> share some
> >> light. Looks like there is an inconsistency
> > 
> > Yes, I noticed that the GPKG specs are rather obscure / unclear
> > about this topic; anyway I received the personal impression that
> > GEOMCOLLECTION was someway the preferred name.
> > (being probably based on the more recents "top secret" ISO
> > SQL/MM specs)
> 
> For better or worse, it's the most specific spec on the topic out there.
> It defines all the types and how the functions on them should behave.
> Even SFS defers to SQL/MM for the details of most things.
> 
> Anyway, in SQL/MM the string 'GEOMETRYCOLLECTION' is only used in the
> WKT encoding. The type name for the same thing is 'ST_GeomCollection'.
> In SFS it's exactly the same, expcet ST_ is stated as being optional
> (see OGC 06-104r4 table 4 and section 7.2.2.2). To make things more
> confusing though the same type is shown as 'GeometryCollection' in
> figure 4. :D
> 
> For GeoPackage specifically I think we should stick to the specs:
> geometrycollection in wkt, geomcollection everywhere else. the
> GeoPackage spec itself is unfortunately, as you pointed out, quite
> inconsistent on the matter. We should get this fixed asap. Paul, what's
> the process to get things started on this?

Pepijn,

just to be sure to fully understand what your position would be : do you mean 
that a table with geom[etry]collection should be registered with 
"GEOMCOLLECTION" as the value of geometry_type_name in gpkg_geometry_columns 
and table 44 would be amended to display "GEOMCOLLECTION" ?

I think I'll change the OGR GPKG driver to accept both on the reading side, 
but it would be good to know what the writing side should do. Currently OGR 
writes GEOMETRYCOLLECTION.

Luckily that shape type is not the more popular one...

Another related question is : what is the SQLite data type that should be 
indicated for a geometry column in a user feature table. Example C.4 / Table 
27 shows "geometry GEOMETRY". Is it GEOMETRY because the "geometry" column 
might contain any type of geometries ? Or if geometry would be a point-only 
column (declared as geometry_type_name = 'POINT' in gpkg_geometry_columns), 
would that be "geometry POINT" ? This must be discussed in 2.1.6.1.2 but I'm 
afraid this is a bit too abstract for me to fully understand by myself...

Thanks

Even

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