[postgis-devel] isvalid(geom), but st_ashexewkb(geom, 'NDR')::geometry fails

[David Fuhry]

Regina,

    Yeah, I agree that the WKT is not valid.  The real question is, is 
the WKB valid?  If not, isvalid() should return false.  If so, the 
parser should parse it without error.

    ST_GeomFromText('MULTIPOLYGON EMPTY') returns a different geometry 
from mine.  Adding the srid makes it a little closer, but not the same. 
  Both of these are correctly identified as st_isempty(), although mine 
is not.

db=> select st_geomfromtext('MULTIPOLYGON EMPTY');
   st_geomfromtext
--------------------
  010700000000000000
(1 row)

db=> select setsrid(st_geomfromtext('MULTIPOLYGON EMPTY'), 3785);
           setsrid
----------------------------
  0107000020C90E000000000000
(1 row)


Thanks,

Dave


Obe, Regina wrote:
> David,
> 
> I don't think that is valid WKT syntax for an EMPTY multipolygon. If I 
> try to stuff that in via ST_GeomFromText it returns invalid geometry. 
> Not sure how you got that in there.
> 
> It should be
> 
>  SELECT ST_GeomFromText('MULTIPOLYGON EMPTY');
> 
> 
> On 1.3.3 and 1.3.4SVN - when I do this - I get the below which is also 
> kind of odd.  I would have expected it to maintain the empty polygon.
> 
>  SELECT ST_IsValid(the_geom), ST_AsText(the_geom), ST_IsEmpty(the_geom), 
> ST_AsEWKT(the_geom)  FROM (SELECT ST_GeomFromText('MULTIPOLYGON EMPTY') 
> As the_geom) As foo ;
>  st_isvalid |        st_astext         | st_isempty |        
> st_asewkt        
> ------------+--------------------------+------------+--------------------------
>  t          | GEOMETRYCOLLECTION EMPTY | t          | GEOMETRYCOLLECTION 
> EMPTY
> (1 row)
> 
> Hope that helps,
> Regina
> -----Original Message-----
> From: postgis-devel-bounces at postgis.refractions.net on behalf of David Fuhry
> Sent: Thu 10/23/2008 11:28 PM
> To: PostGIS Development Discussion
> Subject: [postgis-devel] isvalid(geom), but 
> st_ashexewkb(geom,'NDR')::geometry fails
> 
> I have an empty multipolygon which isvalid(), but which the parser
> throws "ERROR:  geometry requires more points" on.  Is this a bug in
> isvalid(), or in the parser?  Interestingly, st_isempty() returns false.
> 
> db=> select geom from tt;
>                           geom
> ------------------------------------------------------
>   0106000020C90E00000100000001030000000100000000000000
> (1 row)
> 
> db=> select st_astext(geom) from tt;
>         st_astext
> ------------------------
>   MULTIPOLYGON(( EMPTY))
> (1 row)
> 
> db=> select isvalid(geom) from tt;
>   isvalid
> ---------
>   t
> (1 row)
> 
> db=> select st_ashexewkb(geom,'NDR')::geometry from tt;
> ERROR:  geometry requires more points
> 
> db=> select st_isempty(geom) from tt;
>   st_isempty
> ------------
>   f
> (1 row)
> 
> db=> select version(), postgis_version();
>                                          version
>                   |            postgis_version
> -----------------------------------------------------------------------
> -----------------+---------------------------------------
>   PostgreSQL 8.3.1 on i486-pc-linux-gnu, compiled by GCC cc (GCC) 4.2.3
> (Debian 4.2.3-4) | 1.3 USE_GEOS=1 USE_PROJ=1 USE_STATS=1
> (1 row)
> 
> Thanks,
> 
> Dave
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