[postgis-tickets] [PostGIS] #3768: Geometry becomes invalid after a simple shift (black magic)

[PostGIS]

#3768: Geometry becomes invalid after a simple shift (black magic)
------------------------------+---------------------------
 Reporter:  tobiasreber       |      Owner:  pramsey
     Type:  defect            |     Status:  new
 Priority:  medium            |  Milestone:  PostGIS 2.0.8
Component:  postgis           |    Version:  2.1.x
 Keywords:  invalid Geometry  |
------------------------------+---------------------------
 Marcel Clausen and me found out, that one of our geometries became invalid
 after a simple shift ''(ST_Translate(the_geom, 2000000,
 1000000)::geometry)''.

 **Here the valid geometry:**

 select
 st_isvalidreason(st_geometryfromtext('SRID=21781;MULTIPOLYGON(((669054
 215766.1, 669054.8 215766.9, 669095.2 215807.2, 669064 215776.1, 669054
 215766.1)))'));


 **Here the invalid geometry (after a simple shift):**

 select
 st_isvalidreason(st_geometryfromtext('SRID=2056;MULTIPOLYGON(((2669054
 1215766.1, 2669054.8 1215766.9, 2669095.2 1215807.2, 2669064 1215776.1,
 2669054 1215766.1)))'));

 Can someone tell me why the geometry became invalid after the shift?


 Here our installation:
 "POSTGIS="2.1.4 r12966" GEOS="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel. 4.8.0, 6
 March 2012" GDAL="GDAL 1.10.1, released 2013/08/26" LIBXML="2.9.1"
 LIBJSON="UNKNOWN" TOPOLOGY RASTER"

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3768>
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