[postgis-users] Transform overlapping polygons to non-overlapping?

Brent Fraser bfraser at geoanalytic.com
Wed Jul 16 11:20:23 PDT 2008


  Yes! Clean polygons!  I gravitated towards PostGIS due to my large number of polygons (1.2 million), and I'd like a solution that is scalable beyond that number.  GRASS may be the/an answer; I'll give it a try.


Dylan Beaudette wrote:
> On Wednesday 16 July 2008, Brent Fraser wrote:
>> Regina,
>>   I'm not convinced ST_Union is the way to go (using ST_Overlaps OR
>> ST_Intersects as a condition).  Basically I want to iterate over the
>> collection (recursively?) clipping one polygon to another until I'm left
>> with no overlapping (or intersecting) polygons (planar topology).  This is
>> sightly more complicated than the way I originally posed the problem (I
>> wanted to created slivers from the overlapping areas to get planar
>> topology).
>>   A little background:
>> 	My polygons represent a classification of vegetation of a large area of
>> interest.  In theory any point in the area of interest must fall in one and
>> only one polygon.  Due to an artifact of my image segmentation process, my
>> polygons currently have slight overlap which I need to "dissolve" (and I
>> don't care which polygon the overlap sliver gets dissolved into).
>> Thanks!
>> Brent.
> It really sounds like you need to perform some "cleaning" operations in a 
> topologically-aware GIS. Check out the v.clean module in GRASS.
> Cheers,
> Dylan

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