[postgis-tickets] [PostGIS] #4736: ST_NumGeometries is zero for GeometryCollection with empty parts

[PostGIS]

#4736: ST_NumGeometries is zero for GeometryCollection with empty parts
-------------------------+---------------------------
  Reporter:  Mike Taves  |      Owner:  strk
      Type:  defect      |     Status:  assigned
  Priority:  medium      |  Milestone:  PostGIS 3.0.4
 Component:  postgis     |    Version:  2.4.x
Resolution:              |   Keywords:
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Comment (by pramsey):

 Hm, the wiki says that ST_GeometryN(empty, 1) should return empty, but
 that is a bit fiddly, since ST_NumGeometries(empty) returns 0, which maybe
 it should return 1? Since there's one geometry there, and it's an empty
 one?
 {{{
 postgis_reg=# select st_numgeometries('POINT EMPTY');
  st_numgeometries
 ------------------
                 0
 (1 row)

 postgis_reg=# select st_numgeometries('POINT(1 1)');
  st_numgeometries
 ------------------
                 1
 (1 row)
 }}}
 Also, this is inconsistent with num geometries for empty being zero
 {{{
 postgis_reg=# select st_geometryn('POINT EMPTY', 1);
                 st_geometryn
 --------------------------------------------
  0101000000000000000000F87F000000000000F87F
 (1 row)
 }}}
 I'm half-tempted to go with num geometries is 1 for simple objects and n
 -sub-geometries for any collection, even a collection of empties, and make
 the behaviour consistent. Would require updates to the wiki page, but I
 think the angels on the pin dance better that way. Thoughts?

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4736#comment:5>
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