[postgis-users] A way to split polygons?

Peter N. Schweitzer pschweitzer at usgs.gov
Thu Mar 3 13:20:42 PST 2011

On 03/03/2011 04:00 PM, pcreso at 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 N. Schweitzer (MS 954, U.S. Geological Survey, Reston, VA 20192)
(703) 648-6533  FAX: (703) 648-6252  email: pschweitzer at usgs.gov

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