[postgis-users] Some questions concerning postgis

Neil.Young Neil.Young at Freenet.de
Mon Jan 26 23:13:41 PST 2009

Ah, forgot the screenshot. Here it is.

Neil.Young schrieb:
> Hello Leo and Paul,
> thanks for your answers. The data, I have here, consists of 5204 
> polygons, each having a common border with some others (screenshot of 
> the first half attached). The data requires heavy generalization, 
> because it is unnecessary detailed - at least in terms of a planned 
> web based vector map presentation (GM, VE, OSM etc.). I guess, simply 
> "Douglas-Peuker'ing" each polygon isn't helpful, because splits and 
> cavities may be produced by an algorithm, which doesn't mind the 
> semantical context of all the polygons. I've found mapshaper.org 
> (which isn't working with my data) and this 
> http://www.cartoweb.org/downloads/vertexsimplification/documentation.html. 
> I could make the latter run, at least for the first step - the vertex 
> creation. Don't know, what results may arise, because it takes hours 
> to calculate the things, and I currently have no means to "visualize" 
> the results. What would you suggest for visualization? I know 
> mapserver, but do I really have to go this way in order to see the 
> table based data?
> I'm using SQL Server 2008 normally, there is a in-build viewer. Is 
> something similar available for PG?
> Regards
> Paul Ramsey schrieb:
>> On Mon, Jan 26, 2009 at 3:54 PM, Paragon Corporation <lr at pcorp.us> 
>> wrote:
>>> 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.
>> It is hard. Kevin gave a recipe for it once though... perhaps he'll
>> wikify it this time...
>> P
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