I checked the OGC Simple Feature Access specifications.
<URL: http://www.opengeospatial.org/standards/sfa >, and
could not find anything that limits the precision of WKT.
The SFA 1.1.0 spec
<Point> := <x> <y>
<x> := double precision literal
<y> := double precision literal
Double precision literal does not seem to be defined further,
but I would assume that this does not make it impossible to
represent the PostGIS coordinate precision.
The SFA 1.2.0 spec:
<point> ::= <x> <y>
<x> ::= <signed numeric literal>
<y> ::= <signed numeric literal>
<signed numeric literal> ::= {<sign>}<unsigned numeric literal>
<unsigned numeric literal> ::= <exact numeric literal>
|<approximate numeric literal>
<approximate numeric literal> ::= <mantissa>E<exponent>
<mantissa> ::= <exact numeric literal>
<exponent> ::= <signed integer>
<exact numeric literal> ::= <unsigned integer>
{<decimal point>{<unsigned integer>}}
|<decimal point><unsigned integer>
<signed integer> ::= {<sign>}<unsigned integer>
<unsigned integer> ::= (<digit>)*
This BNF gives no limit to the number of digits used before or after
the decimal point. I have not found anything that limits the number
of digits.
Håvard
Obe, Regina wrote:
Havard,
I think as Mark mentioned if it did it would violate the spec. I think
somewhere in the spec is some specification of guaranteed precision of
WKT and if there isn't - text can never represent floating to complete
accuracy. The AsBinary I think on the other hand is exact fidelity. So
simply trying to make them equal would probably irritate people who need
precision higher than what the WKT spec offers.
In my particular case of course this would be ideal - but I can't be
selfish :)
So I can live with the general rule that
ST_GeomFromText(ST_AsText(geom), srid here) != geom
As long as I can override it by updating my millions of geometries to
so and 300 someodd tables with
SET the_geom = ST_GeomFromText(ST_AsText(geom))
without too many weird side effects. I may just try it and see if it
causes other problems elsewhere.
testing with the badly edited records it seems to at least make my
other geometries just as inprecise as the edited ones so I get
intersection where I should again.
Thanks,
Regina
------------------------------------------------------------------------
*From:* [EMAIL PROTECTED] on behalf of
Havard Tveite
*Sent:* Fri 5/16/2008 2:41 PM
*To:* PostGIS Users Discussion
*Subject:* Re: [postgis-users] Does ST_AsText truncate or round
Sorry, for not making much sense here. What I wanted to
say was that ST_AsText(geom) should be equivalent to geom,
meaning that if you go from the database/binary
representation of the geometry to the text representation
of the geometry (using ST_AsText) and then back to the
database/binary representation (using ST_GeomFromText),
you should end up with the same geometry that you
started out with. This is important for applications
that use when WKT when talking to PostGIS.
Håvard
Mark Cave-Ayland wrote:
> Håvard Tveite wrote:
>> ST_GeomFromText(ST_AsText(geom)) != geom
>>
>> sounds like a bug to me (ignoring the SRS).
>>
>> Håvard
>
> No, since the SFS 1.1 specification supports only 2 dimensions with no
> SRS (and ST_AsText() is spec compliant). If you need the SRS then you
> should use the PostGIS-enhanced ST_EWKT() function which will output the
> extra information, but is not spec-compliant.
>
>
> ATB,
>
> Mark.
>
> --
> Mark Cave-Ayland
> Sirius Corporation - The Open Source Experts
> http://www.siriusit.co.uk <http://www.siriusit.co.uk/>
> T: +44 870 608 0063
> _______________________________________________
> postgis-users mailing list
> [email protected]
> http://postgis.refractions.net/mailman/listinfo/postgis-users
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