[geos-devel] [GEOS] #531: UnaryUnion of an line collapsed to a point returns EMPTY

[GEOS]

#531: UnaryUnion of an line collapsed to a point returns EMPTY
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 Reporter:  strk        |       Owner:  geos-devel@…
     Type:  defect      |      Status:  closed
 Priority:  major       |   Milestone:  3.8.0
Component:  Default     |     Version:  3.3.3
 Severity:  Unassigned  |  Resolution:  wontfix
 Keywords:              |
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Comment (by mdavis):

 Yes, perhaps it is inconsistent.   Tricky to know what the right semantic
 should be.

 The fact that collapsed LineStrings are actually invalid muddies the water
 even more, since returning a single-point LineString would violate the
 principle of always returning a valid geometry.  This is actually one
 difference to the JTS 476 issue, since in that case the inputs are valid.
 Although the invalidity of single-point LineStrings has always struck me
 as overly-limiting.

 There's an appeal to returning *something* non-empty, to indicate that
 there are actual vertices in the input, which should not just disappear.
 So then should a POINT be returned, or hold our nose and return a single-
 point LINESTRING?

 I'm not sure there is a single answer which address all requirements.
 Providing a strict mode in addition to full mode might satisfy more
 people.  But that's a lot more complexity.

-- 
Ticket URL: <https://trac.osgeo.org/geos/ticket/531#comment:8>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).