[postgis-devel] Canonical binary form AND WKB

[strk at refractions.net]

On Tue, Dec 21, 2004 at 04:55:35PM -0000, Mark Cave-Ayland wrote:
> Hi strk,
> 
> > -----Original Message-----
> > From: postgis-devel-bounces at postgis.refractions.net 
> > [mailto:postgis-devel-bounces at postgis.refractions.net] On 
> > Behalf Of strk at refractions.net
> > Sent: 21 December 2004 15:23
> > To: Markus Schaber
> > Cc: PostGIS Development Discussion
> > Subject: Re: [postgis-devel] Canonical binary form AND WKB
> 
> (cut)
> 
> > Ok. I've reverted canonical binary form (and bytea casts) 
> > back to EWKB input/output and extended EWKB with a SRID 
> > presence flag and int4 storage (if present) right after wkbtype.
> 
> So basically EKWB is our "on the wire" version of LWGEOM, but abstracted so
> that if we change LWGEOM internally, it won't have a knock-on effect on
> EWKB.
> 
> > HEXEWKB does not need SRID=#; anymore, but still accepts it 
> > for old dumps.
> 
> Great. If we can't read the geometry, there seems little point in having the
> SRID in readable format ;)
>
> > What is left now is *strict* OGC WKB I/O.
> > For output we can just *downgrade* geometries to be OGC 
> > compliant (strip Z,M and SRID) very easily. For input I'm 
> > afraid we'll need a separate parser, to allow for EWKB 
> > <future>WKB clashes. I guess this can be done when WKB-ng is 
> > out (why run?).
> 
> Great, so at least we are now import/export compliant. Perhaps Extended
> WKB/WKT are slightly misleading names.... Other than that, I think we need
> to document why we made all the decisions leading up to this, and give clear
> definitions of LWGEOM, EWKB/T etc. and confirm the strict OGC-compliancy of
> the existing functions.

Ok. I've made asText(geometry) and asBinary(geometry, {XDR|NDR}) strict ogc
and provided asEWKT(geometry) and asEWKB(geometry, {XDR|NDR}) for explicit
output of our extended versions.

GeometryFromText and GeometryFromWKB still accept EWKT/EWKB forms, which
are supersets of WKT/WKB (thus the name). This is not a problem until
OGC releases it's new no-more-compatible specification...

Now some tests, documentation and finally performance tuning.

> 
> Well done strk!
> 

Thanks.
--strk;

> 
> 
> Kind regards,
> 
> Mark.
> 
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