Geometry Boost List: [ggl] WKT empty

Subject: [ggl] WKT empty
From: Hartmut Kaiser (hartmut.kaiser)
Date: 2009-06-12 17:46:06

> 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.

Regards Hartmut