[PostGIS] #5781: Concave Hull returning multi poly with polygons

[PostGIS]

#5781: Concave Hull returning multi poly with polygons
----------------------+---------------------------
  Reporter:  latot    |      Owner:  pramsey
      Type:  defect   |     Status:  new
  Priority:  medium   |  Milestone:  PostGIS 3.4.4
 Component:  postgis  |    Version:  3.4.x
Resolution:           |   Keywords:
----------------------+---------------------------
Comment (by robe):

 I thought this was an issue with the old geos, but looking at a server I
 have running:


 {{{
 POSTGIS="3.4.1 3.4.1" [EXTENSION] PGSQL="150" GEOS="3.12.1-CAPI-1.18.1"
 SFCGAL="SFCGAL 1.5.0, CGAL 5.6, BOOST 1.78.0" PROJ="8.2.1
 NETWORK_ENABLED=OFF URL_ENDPOINT=https://cdn.proj.org
 USER_WRITABLE_DIRECTORY=C:\Users\paragon\AppData\Local/proj
 DATABASE_PATH=C:\Program
 Files\PostgreSQL\15\share\contrib\postgis-3.4\proj\proj.db"
 LIBXML="2.9.14" LIBJSON="0.12" LIBPROTOBUF="1.2.1" WAGYU="0.5.0
 (Internal)"
 }}}


 However passing 0 for shrink percent I'm tempted to say should be illegal,
 so it's probably treating that as a no op. Maybe we should just prevent 0
 from being passed in.
 For example if I do:


 {{{
 SELECT ST_AsText(ST_ConcaveHull(

     ST_COLLECT(

         array[

             'POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))'::geometry, 'POLYGON((10
 10, 11 10, 11 11, 10 11, 10 10))'::geometry

         ]

     ), 0.8

 ));
 }}}


 I get:


 {{{
 POLYGON((10 11,11 11,11 10,10 10,1 0,0 0,0 1,1 1,10 11))
 }}}


 and shows me visually what I would expect.
-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/5781#comment:1>
PostGIS <http://trac.osgeo.org/postgis/>
The PostGIS Trac is used for bug, enhancement & task tracking, a user and developer wiki, and a view into the subversion code repository of PostGIS project.