[postgis-users] Simplify borders

[Frederik Ramm]

John,

On 12/10/10 00:04, John Abraham wrote:
> I'm sure this is a common problem, but I haven't been able to figure
> out how to do it in PostGIS.

One way to do it - used by me in the past, but I have no clue if this is 
the best or even an usual way - is to switch your model from "one 
polygon per zone" to "a number of border lines, each dividing two 
zones". This can easily be accomplished by intersecting each polygon 
with all others (the outer boundaries of the region will require special 
handling but not too difficult either). Resulting line geometries must 
have two columns "zone1" and "zone2" that tell you which zones are 
divided by that line.

Then you can simplify the resulting mesh of lines to your heart's 
content, provided that the simplification algorithm does not change the 
first and last point.

Afterwards, for each zone you collect all lines that have the zone id in 
"zone1" or "zone2" into a (multi)polygon, and there you are. This 
process ensures that there will never be any no man's land or overlap 
between zones.

Bye
Frederik