[postgis-devel] Typmod Again

[Paul Ramsey]

32 bits:
Top 24 bits for SRID,
Middle 6 bits for Type,
Bottom 2 bits for Z/M flags.

The difficulty is not doing typmod, it's doing it without breaking
backwards compatibility. I'm also currently running into some oddness
with PgSQL not handing me the typmod in the _in function (which is
required to enforce the restriction), even though one is defined on
the column.

There's some issues in general with typmod, I fear, which is that a
typmod is not a constraint. Where is it enforced? It seems like only
in the _in function, which just protects the on inserts from text.

If I do

UPDATE mytable SET thegeom = ST_SetSRID(thegeom, 1111)

and 1111 is not my SRID typmod, what happens?

P.

On Wed, Jul 22, 2009 at 4:50 PM, Stephen Frost<sfrost at snowman.net> wrote:
> Paul,
>
> * Paul Ramsey (pramsey at opengeo.org) wrote:
>> FYI, I'm implementing this stuff within the context of GEOGRAPHY,
>> which allows us to sort of play with these ideas before rolling them
>> onto GEOMETRY in a breaking way. I do think that trying to hew closer
>> to the standards base for GEOMETRY when we do the 2.0 release would be
>> a good idea, try to put all the breaking changes we can think of into
>> one release.
>
> I've been meaning to work on the typmod stuff for quite some time, but
> have just been way too busy. :/
>
> What's your implementation plan?  Will you be using a side-table for
> each distinct typmod used in the system, or trying to encode the full
> typmod into an integer?  If the dimension can be derived from the type,
> it might be entirely possible to fit the rest into an integer, provided
> an SRID isn't required to allow for a full integer itself.  I don't
> recall ever getting an answer to how big an SRID is allowed to be..
>
> Do you need help with it?  Is there a spec somewhere already that
> details your approach?
>
>        Thanks,
>
>                Stephen
>
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