[postgis-users] Some questions concerning postgis

Paragon Corporation lr at pcorp.us
Mon Jan 26 15:54:19 PST 2009


Not sure I understand your question on number 2.  I assume you are looking
for something like ST_SimplifyPreserveTopology, but maybe you are looking
for something 
Slightly more complicated.

Take a look and see if this answers your question

One caveat.  Don't simplify in long lat projection.  It is best to transform
say back to your other projection, simplify in that projection and then
transform back.


SELECT ST_Transform(ST_SimplifyPreserveTopology(ST_Transform(the_geom,
somemeterorfeetsrid), 0.5))
FROM sometable 

Though if you want to maintain borders I guess you would probably want to
1)  convert your polygons to linestrings using ST_Boundary, 
2) dump out into edges and grouping by the gid 
3) Simplify and then repolygonize.

Hmm that sounds hard.  I will have to give that more thought.


-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Sent: Monday, January 26, 2009 4:26 PM
To: PostGIS Users Discussion
Subject: [postgis-users] Some questions concerning postgis

Now, that I have valid data in my db, the following questions arise:

1) The projection of the data is Gauss Krüger III. Possible to re-project to
lets say EPSG 4326?
2) The polygons contain too much vertices. I would like to reduce it, but
keep the common borders valid. Does anybody know, how this could be


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