[postgis-users] simplify weirdnesses

[Markus Schaber]

Hello,

See the following:

logigis=# select count(*), vbef, vafter from (select isvalid(geom) as
vbef, isvalid(simplify(geom,0.05)) as vafter from admin_area_bnd) as
temp group by vbef,vafter; 

 count  | vbef | vafter 
--------+------+--------
   2283 | t    | f
 205495 | t    | t
  65087 | t    | 
(3 rows)

Is it desired that a PostGIS operation on valid geometries can make them
non-valid?

And it seems that some (well, 65 thousand) Geometries even get
deleted by simplify. 

As another example shows, the size of the deleted geometries can be
much larger than the given simplification threshold:

logigis=# select box3d(geom) from admin_area_reconstruct where
simplify(geom,0.05) is null;

                            box3d
-------------------------------------------------------------
BOX3D(5.95587 45.81802 1.7e-308,10.49203 47.80838 1.7e-308) 
(1 row)

Can you explain this?

Thanks,
Markus

-- 
markus schaber | dipl. informatiker
logi-track ag | rennweg 14-16 | ch 8001 zürich
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