[postgis-users] Aggregate funtions

[lucas_postgis]

Dear PostGIS users,

I have a map with polygons which are overlapping among them (original map).
I want to calculate the number of patches or fragments (defining
patch/fragment as polygons wich are overlaping, and/or have common
nodes/borders, and/or are at a distance of less than 1000 meters).

I have thought in follow these steps:
1) Apply an aggregation funtion for aggregating polygons which are
overlapping, or have common nodes/borders. Here we will get the continuous
fragments.(Result= aggregated file)
2) Calculate a buffer of distace = 1000 m over the original map. (Result=
buffer file)
3) Apply an aggregation funtion to the buffer file for aggregating polygons
which are overlaping. (Output= aggregated buffer file)
4) Make an intersect between aggregated buffer file with the aggregated
file. 

I'm stuck with the aggregation funtions. I have the following aggregation
funtions and I don´t obtain the target result:
     
	ST_Accum - Aggregate. Constructs an array of geometries.
    ST_Collect - Return a specified ST_Geometry value from a collection of
other geometries.
    ST_Extent - an aggregate function that returns the bounding box that
bounds rows of geometries.
    ST_Extent3D - an aggregate function that returns the box3D bounding box
that bounds rows of geometries.
    ST_MakeLine - Creates a Linestring from point geometries.
    ST_MemUnion - Same as ST_Union, only memory-friendly (uses less memory
and more processor time).
    ST_Polygonize - Aggregate. Creates a GeometryCollection containing
possible polygons formed from the constituent linework of a set of
geometries.
    ST_Union - Returns a geometry that represents the point set union of the
Geometries.

I´m using Postgre 9.1 for 64 bits with PostGIS 2.0 in Windows 7. I am new in
using PostGIS but after a few days testing SQL instructions I have no more
ideas to solve this problem. Has anyone examples or guidance?

I hope you can help me,

thanks in advance,


Pablo Lucas

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