[postgis-tickets] [PostGIS] #4598: spurious results of ST_Centroid on invalid polygons of type geography

[PostGIS]

#4598: spurious results of ST_Centroid on invalid polygons of type geography
---------------------+---------------------------
 Reporter:  fadi     |      Owner:  pramsey
     Type:  defect   |     Status:  new
 Priority:  medium   |  Milestone:  PostGIS 2.5.4
Component:  postgis  |    Version:  3.0.x
 Keywords:           |
---------------------+---------------------------
 The following query:
 {{{
 WITH geogs (geog) AS (VALUES
     ('POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))'::geography),
     ('POLYGON((0 0, 1 1, 1 1, 0 0))'::geography),
     ('POLYGON((0 0, 1 1, 1 0, 0 1, 0 0))'))
 SELECT
     pg_typeof(geog),
     ST_IsValidReason(geog::geometry),
     ST_AsText(ST_Centroid(geog)),
     ST_AsText(ST_Centroid(geog::geometry)),
 FROM geogs;
 }}}
 will output :
  ||pg_typeof ||             st_isvalidreason              ||
 st_astext                  ||   st_astext  ||
  ||geography || Valid Geometry                            ||
 POINT(0.499999916440062 0.500006427946943) ||POINT(0.5 0.5)||
  ||geography || Too few points in geometry component[0 0] ||POINT(-nan
 nan)                             ||POINT(0.5 0.5)||
  ||geography || Self-intersection[0.5 0.5]                ||POINT(0.5
 0.333342264894616)                ||POINT(0.5 0.5)||
 (3 rows)

 * The first one seems okay, assuming the numbers are due to numerical not
 very
 precise calculation, although I would have expected the centroid some
 where
 between 0 and 0.5 in terms of latitude (the polygon is thicker at the
 bottom)
 * Second and third do not look right.
 {{{
 $ select postgis_full_version();
 }}}

 POSTGIS="3.0.0 r17983" [EXTENSION] PGSQL="120" GEOS="3.7.1-CAPI-1.11.1
 27a5e771" PROJ="Rel. 4.9.2, 08 September 2015" GDAL="GDAL
 1.11.3, released 2015/09/16" LIBXML="2.9.3" LIBJSON="0.11.99"
 LIBPROTOBUF="1.2.1" WAGYU="0.4.3 (Internal)" RASTER

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4598>
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