[postgis-users] (Bug?) Strange Behavior with ST_SymDifference (line, surface)

[Rémi Cura]

hey,
I'm experiencing a strange behavior with ST_SymDifference
:<http://postgis.net/docs/manual-2.0/ST_SymDifference.html>

When doing symdiff of a line and a surface, I get the same surfaces with
added points on surfaces boundary (where line crossed surface).

Example :
  ___________
*├---------┤*
  -------------------

gives
  ___________
*|             |***
  -------------------

I read the SQL MM definition
(here<http://jtc1sc32.org/doc/N1101-1150/32N1107-WD13249-3--spatial.pdf‎>,
page 67-68-69), and I found no trace of behavior with line against
surfaces.

Mathematically , if we take for definition the union without the
intersection, the result is false (no point on the line should be in the
result, yet they are).

I was expecting as output one polygon each side of the line (ie 2 polygons).

I would appreciate any thoughts about this.
Cheers,

Rémi-C
PS : I know I can use ST_Split or other tricks for the same result in this
simple case, but not so easily for trickier case.
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