[postgis-devel] Canonical binary form AND WKB

[Markus Schaber]

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.

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.

Markus
-- 
markus schaber | dipl. informatiker
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