[postgis-devel] Canonical binary form AND WKB

[strk at refractions.net]

On Mon, Dec 20, 2004 at 01:26:30PM +0100, Markus Schaber wrote:
> Hi, all,
> 
> On Fri, 17 Dec 2004 19:28:53 +0100
> strk at refractions.net wrote:
> 
> > > > Another question is how to distinguish between an OGC WKB 
> > > > (extended or not) and a canonical form, which are currently 
> > > > both of type bytea. 
> > > 
> > > The only option I can think of would be to change the canonical form endian
> > > identifiers from 0x00/0x01 to something like 0x80/0x81; then if the first
> > > byte > 0x80 then we know we are dealing with canonical form, otherwise we
> > > assume it is (E)WKB. Having said that, is it possible to tell the difference
> > > between EWKB and WKB?
> > 
> > I agree with Markus actually... if OGC will extend WKB we'll end up
> > with bad conflicts between our extension and their extension.
> > We'd better leave WKB forms driven by OGC and just use byte casts
> > and _recv/_send for out own extensions.
> > 
> > This would mean *dropping* EWKB support as a whole and document
> > canonical binary form for clients willing to support that.
> > Also the same thing should be done with EWKT in GeometryFromWKT().
> 
> You should notice that the client does not really lose any functionality
> this way, as (s)he always can call geometry_send(), geometry_receive(),
> geometry_in() and geometry_out() explicitly when needed. The only
> difference is that he has to parse the new canonical rep instead of
> EWKT/EWKB.

You can't directly call geometry_receive(), as it uses internal datatypes.
I've provided bytea::geometry cast for this purpose.

> But usually, clients will be either plain OpenGIS (and then expect plain
> WKT/WKB using GeometryFromText et al), or will be PostGIS aware and rely
> on the canonical representations created by PostgreSQL implicitly.

See also my latest proposal of making EWKB==native_LWGEOM

--strk;

> 
> Markus
> -- 
> markus schaber | dipl. informatiker
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