SDO_AGGR_UNION of polygons result a geometry with a line segment inside?

Question

Hi,
I am struggling with a problem, I cannot find the reason.
I have 3 polygons in Oracle Spatial 11g (Enterprise Edition Release 11.1.0.7.0 - 64bit Production):
All three are simple polygons: SDO_GEOMETRY(2003, null, null, (1,1003,1), (... coord array...) )
They are valid as the result of an SDO_MIGRATE.TO_CURRENT and a VALIDATE_GEOMETRY_WITH_CONTEXT
SELECT SDO_AGGR_UNION(SDOAGGRTYPE(GEOM, 5E-1)) FROM ....
result a collection geometry with elem_info_array (1,2,1, 5,1003,1)
I cannot understand, how can this happen. Unioning the three separate polygons should result a simple polygon (if they were touching/overlapping) or a multipolygon with 2 or 3 rings.
But the unionig how can result a line segment of two points??
I have double-checked the polygons and the tolerance values also.
Have you any idea?
Thanks is advance
Regards,
Tamas

Answer 1

They're some crazy looking geometries you've got there! I got a geometry back from your query using 11.1.0.6 on Windows XP, but its a useless geometry. I wouldn't expect Oracle Spatial to come back with a sensible geometry at the end of this anyway. You've got a mix of lots of different geometry types.
SQL> select t.geometry.sdo_gtype, count(*)
  2  from test_geomunion t
  3  group by t.geometry.sdo_gtype
  4  order by 1;
GEOMETRY.SDO_GTYPE   COUNT(*)
              2001        355
              2002        499
              2003       1649
              2004         11
              2006          2
              2007         21What result would you expect from the sdo_aggr_union query? i.e. what purpose would unioning all these together serve?
I would more usually use sdo_aggr_union to put merge a few contiguous polygons together. Unioning points, lines and polygons together doesn't make sense to me.