[postgis-users] ConcaveHull generation

[Brian Sanjeewa Rupasinghe]

Hi,

I have two polygons with following coordinates:

poly1: (13,0 13,20 23,20 23,0 13,0)

poly 2: (23,20 23,28 30,28 30,20 23,20)

Once generated concaveHull, i end up with the polygon having following
coordinates:

"POLYGON((13 3e-016,13 5.64256204109163,13 11.2851240821833,13
16.9276861232749,13 20,17.4061007032357 20,23 27.049761125177,23
28,28.6425620410916 28,30 28,30 22.3574379589084,30 20,23
14.674220666202,23 9.34844133240395,23 4.02266199860593,23
3e-016,17.3574379589084 3e-016,13 3e-016))"


When investigating the coordinate list, it is observed that some existing
edges are split. [Eg. edge connecting 13,0 and 13,20]. Why is taht?


Here is the SQL code i used


SELECT ST_AsText (ST_cleangeometry((ST_ConcaveHull(ST_Collect(geom),
0.99))))

FROM concavepoly

WHERE cluster_id = 'VC-2';


Cheers, Brian
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