[postgis-users] Intersection of point and linestring. Error?

[ksa]

Hi, List.

I have a table that contains two multilinestrings (where numgeometries = 1);
And I have some problem.

search=# select gid, geom from t_table_46;
 gid |
geom
-----+----------------------------------------------------------------------
----------------------------------------------------------------------------
----------------------------------------------------------------------------
------------------
   1 |
SRID=2000;MULTILINESTRING((-346.39495192 -32.22278924,-346.39495192 -32.2227
8924,-347.01462094 37.18014143,-261.50029565 23.54742291,-271.41500003
93.5700226,-187.14001279 74.36028286,-195.1957101 155.53692498,-118.97642017
141.90420646))
   2 | SRID=2000;MULTILINESTRING((-268.94877508 161.46993124,-268.94877508
161.46993124,-236.16352798 88.61382659,-238.34921112 24.5004545))
(2 rows)

This multilinestrings have intersection.
search=# select geometryfromtext(astext(intersection(t1.geom, t2.geom)),
2000) from t_table_46 t1, t_table_46 t2 where t1.gid = 1 and t2.gid = 2;
                  geometryfromtext
----------------------------------------------------
 SRID=2000;POINT(-236.267686750346 85.558502660642)
(1 row)

So, there is a point that lays on one multilinestring and on second
multilinestring. And I think that intersection of this point and
multilinestring *must* be point (same point). But I havebad result after
executing next query...

search=# select intersection(geom, (select
geometryfromtext(astext(intersection(t1.geom, t2.geom)), 2000) from
t_table_46 t1, t_table_46 t2 where t1.gid = 1 and t2.gid = 2)) from
t_table_46;
           intersection
-----------------------------------
 SRID=-1;GEOMETRYCOLLECTION(EMPTY)
 SRID=-1;GEOMETRYCOLLECTION(EMPTY)
(2 rows)

Why? I think the result must be:
                  geometryfromtext
----------------------------------------------------
 SRID=2000;POINT(-236.267686750346 85.558502660642)
 SRID=2000;POINT(-236.267686750346 85.558502660642)
(2 row)


Sergey Karin