Subject: [ggl] WKT empty
From: Barend Gehrels (barend.gehrels)
Date: 2009-06-12 18:18:05
>> About WKT support. Many applications / libraries / databases support
>> the
>> option "EMPTY", so
>> LINESTRING EMPTY
>> POLYGON EMPTY
>> for empty geometries.
>>
>> I cannot find that in the OGC specifications (if someone knows the
>> document number, it is welcome).
>>
>> However, if many do it might be reason enough to support it. We support
>> LINESTRING() and POLYGON(()) for an empty line or polygon, and a
>> POINT()
>> will result in a point with zero-values. But adding EMPTY will increase
>> interoperability.
>>
>
> WKT Geometry is specified in the 'OpenGIS Implementation Specification for
> Geographic information - Simple feature access - Part 1: Common
> architecture' (http://portal.opengeospatial.org/files/?artifact_id=18241).
> >From looking at the BNF there (page 53) I gather EMPTY is an allowed
> construct for any type of geometry.
>
>
Thanks Hartmut. Now I see it, it is there indeed. Besides that, our
LINESTRING() is probably not valid. No problem to interpret it, but we
should not generate it that way.
Regards, Barend