[postgis-tickets] [PostGIS] #4738: ST_Union creates wrong result

[PostGIS]

#4738: ST_Union creates wrong result
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  Reporter:  laopsahl  |      Owner:  pramsey
      Type:  defect    |     Status:  new
  Priority:  medium    |  Milestone:  PostGIS 3.1.0
 Component:  postgis   |    Version:  3.0.x
Resolution:            |   Keywords:
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Comment (by laopsahl):

 I have testing some more and I see this behaviour

 If test all lines with id less than 500 it seem to be OK.


 {{{
 select (ST_Dump(ST_Union(i.geom))).geom from
 ( select geom from test_input_snap where id < 500 ) as i

 }}}

 It also seem ok with all between 200 and 600.


 {{{
 select (ST_Dump(ST_Union(i.geom))).geom from
 ( select geom from test_input_snap where id > 200 and id < 600 ) as i

 }}}

 But if I try to out lines between 100 and 600 it starts to snap.


 {{{
 select (ST_Dump(ST_Union(i.geom))).geom from
 ( select geom from test_input_snap where id > 100 and id < 600 ) as i

 }}}

 I now tested on
 POSTGIS="3.0.0 r17983" [EXTENSION] PGSQL="120" GEOS="3.8.0-CAPI-1.13.1 "
 PROJ="6.3.0" LIBXML="2.9.10" LIBJSON="0.13.1" LIBPROTOBUF="1.3.2"
 WAGYU="0.4.3 (Internal)" TOPOLOGY

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4738#comment:1>
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