Evan,
Here is the old post about tiling polygons. There may be others also.
0Steve
On 3/3/2011 7:03 PM, Arnold Helmut Engelmann wrote:
If you want to go the tiling route and want to try that: Create a layer of
tiles (boxes) at the size you want. Then run the following query:
CREATE TABLE
tiled_geo_units as
SELECT
ST_Intersection(a.geometry, b.geometry) AS geometry,
a.*,
b.*
FROM
geo_units as a,
tiles as b
WHERE
ST_Intersects(a.geometry, b.geometry)
Where "geo_units" is the table with your geological units, and "tiles" is the table of
boxes you created. This will intersect both layers and split the polygons at the tile boundaries. You can
also add to the WHERE clause if you want to filter out just the "large" polygons, otherwise this
will tile all your polygons. For this ST_NPoints will probably useful.
Arnold
-----Original Message-----
From: postgis-users-boun...@postgis.refractions.net
[mailto:postgis-users-boun...@postgis.refractions.net] On Behalf Of Peter N.
Schweitzer
Sent: Thursday, March 03, 2011 13:21
To: pcr...@pcreso.com
Cc: PostGIS Users Discussion
Subject: Re: [postgis-users] A way to split polygons?
On 03/03/2011 04:00 PM, pcr...@pcreso.com wrote:
It sounds like you are wanting to tile your polygons. Not really ideal, as each
polygon is rendered via tiles, so you need to render them without borders to
hide the tiles, then often plot the border as well, which still has all the
vertices. Lots more work.
Hmmm. But in my KML, I'm not drawing the boundaries, so perhaps that
disadvantage doesn't cause trouble in this situation?
You might look at simplifying your polygons to reduce the number of vertices in
each. If you manage your data topologically, this process will work better at
retaining shared boundaries.
Mike Toews has suggested ST_Simplify or ST_SimplifyPreserveTopology, but I'm
unsure of what value to use for the tolerance. The CRS is geographic, not
projected.
If you can use Google to provide vector zoom layers, then as you zoom
in you can get less& less simplified versions... just like pyramid'ed
rasters. Zoomed out you can't see so don't provide the unnecessary detail.
Use Google? I don't understand--is there some service they provide which might be used
for data like these? Or are you referring to a way to describe the data in KML that I'm
not familiar with? Either is plausible--I'm not being snarky here! I'm just writing KML
with a PHP script that queries the PostgreSQL db, and have used these technologies in
only simple ways so far. So when I say "Google" I mean only that the people
who use these data typically open them with Google Earth, at least, those who experience
this problem report it so.
Peter
--
Peter N. Schweitzer (MS 954, U.S. Geological Survey, Reston, VA 20192)
(703) 648-6533 FAX: (703) 648-6252 email:
pschweit...@usgs.gov<http://geology.usgs.gov/peter/>
_______________________________________________
postgis-users mailing list
postgis-users@postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users
_______________________________________________
postgis-users mailing list
postgis-users@postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users
_______________________________________________
postgis-users mailing list
postgis-users@postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users
