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List:       postgis-users
Subject:    Re: [postgis-users] simple polygon clip
From:       Hugues François <hugues.francois () irstea ! fr>
Date:       2014-11-10 12:14:10
Message-ID: 10a001cffcdf$df90e67a$5568ddc3 () cemagref ! fr
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Hi,

I think you might add a where st_intersects(aoi.geom, line_buffer.geom). If not, your \
query returns differences between each polygon and each line even if they do not \
intersect. In this case the difference between the polygon and nothing is the \
original polygon.

You might also take care when a polygon intersects different lines since your query \
will return as many differences as the number of intersections. One solution is to \
union intersected lines.

Hugues

Le 10 nov. 2014 12:58, Christopher Braune <chbraune@uni-potsdam.de> a écrit :
> 
> Dear all,
> 
> I want to clip polygons like this:
> 
> 
> I tried the following SQL-sentences:
> 
> CREATE TABLE Dear all,

I want to clip polygons like this:


I tried the following SQL-sentences:

CREATE TABLE aoi_blocks AS
SELECT *,
     ST_Difference(aoi.geom, lines.buffer_geom)
     FROM aoi, lines;

I get polygons, but not only the difference polygons!

Thanks for all replies!
Christopher
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