[postgis-devel] wkb geometry type codes: PostGIS vs OGC

[Raven Kopelman]

Hi Paul,

While your response is exactly what I would have hoped for, it does
call my ability to read WKB into question.

The following are query/result pairs as run through pgAdmin III,
against PostGIS 1.5

select ST_AsBinary(ST_GeometryFromText('COMPOUNDCURVE(CIRCULARSTRING(0
0, 1 1, 1 0),(1 0, 0 1))', 4236));
"\001\011\000\000\000\002\000\000\000\001\010\000\000\000\003\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\360?\000\000\000\000\000\000\360?\000\000\000\000\000\000\360?\000\000\000\000\000\000\000\000\001\002\000\000\000\002\000\000\000\000\000\000\000\000\000\360?\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\360?"

select ST_AsBinary(ST_GeometryFromText('CURVEPOLYGON(CIRCULARSTRING(0
0, 4 0, 4 4, 0 4, 0 0),(1 1, 3 3, 3 1, 1 1))', 4236));
"\001\015\000\000\000\002\000\000\000\001\010\000\000\000\005\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\020@\000\000\000\000\000\000\000\000\000\000\000\000\000\000\020@\000\000\000\000\000\000\020@\000\000\000\000\000\000\000\000\000\000\000\000\000\000\020@\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001\002\000\000\000\004\000\000\000\000\000\000\000\000\000\360?\000\000\000\000\000\000\360?\000\000\000\000\000\000\010@\000\000\000\000\000\000\010@\000\000\000\000\000\000\010@\000\000\000\000\000\000\360?\000\000\000\000\000\000\360?\000\000\000\000\000\000\360?"

In the case of the compound curve, I see a geometry type of \011 which
I believe means 9, which matches the OGC as well as liblwgeom.h.

In the case of the curve polygon, I see a geometry type of \015 which
I believe means 13, which matches liblwgeom.h, but not the OGC.
Multicurve and Multisurface are similarly "off".

If you can point out my error I would greatly appreciate it.

Thanks,
Raven


On Tue, May 4, 2010 at 5:14 PM,
<postgis-devel-request at postgis.refractions.net> wrote:
> Message: 5
> Date: Tue, 4 May 2010 14:19:00 -0700
> From: Paul Ramsey <pramsey at cleverelephant.ca>
> Subject: Re: [postgis-devel] wkb geometry type codes: PostGIS vs OGC
> To: PostGIS Development Discussion
>        <postgis-devel at postgis.refractions.net>
> Message-ID:
>        <y2h30fe546d1005041419qa0926deaze1911f76efd600e7 at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Raven,
>
> The WKB emitted by PostGIS will use the standard OGC type codes. The
> internal structure of PostGIS will use its own type codes. Even the
> EWKB emitted by PostGIS will use the OGC type codes. So your parser
> shouldn't know/care what values we have in liblwgeom.h
>
> Yours,
>
> Paul
>
> On Tue, May 4, 2010 at 2:10 PM, Raven Kopelman <raven.kopelman at safe.com> wrote:
> > Hi PostGIS developers,
> >
> > I'm working on PostGIS support for Safe Software's FME and have a couple
> > questions about the way PostGIS does things.
> >
> > In particular, it looks like the WKB geometry type codes used by PostGIS
> > don't line up with those specified by the OGC.
> >
> > For example, from liblwgeom.h:
> >>
> >> #define CURVEPOLYTYPE 13
> >> #define MULTICURVETYPE 14
> >> #define MULTISURFACETYPE 15
> >
> > Whereas the OGC has
> >>
> >> CurvePolygon 10
> >> MultiCurve 11
> >> MultiSurface 12
> >> Curve 13
> >> Surface 14
> >> PolyhedralSurface 15
> >
> > SQLMM of course offers some completely different alternate choices,
> > something like:
> >>
> >> CurvePolygon 1000003
> >> Multicurve 1000004
> >> Multisurface 1000005
> >
> > which, if I recall the values correctly, have an unexpected (and possibly
> > coincidental) alignment with the PostGIS choices...
> >
> > I'm curious about this apparent discrepancy, and what it implies about my
> > chances of keeping our WKB parser more or less vendor neutral.
> >
> > And I haven't tested this yet, but I presume that ST_AsBinary() will return
> > the same PostGIS specific type codes as ST_AsEWKB()?
> >
> > Thanks,
> > Raven
> >
> > _______________________________________________
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