[postgis-devel] [PostGIS] #832: Wrong line from ST_Difference

[PostGIS]

#832: Wrong line from ST_Difference
-----------------------+----------------------------------------------------
 Reporter:  aperi2007  |       Owner:  pramsey      
     Type:  defect     |      Status:  new          
 Priority:  medium     |   Milestone:  PostGIS 2.0.0
Component:  postgis    |     Version:  trunk        
 Keywords:             |  
-----------------------+----------------------------------------------------
 I notice this strange results:

 If I try this sql:

 {{{
 SELECT ST_AsText(
 ST_Difference(
 ST_GeomFromText('LINESTRING(50 49.9999999999999, 50 200)'),
 ST_Intersection(ST_GeomFromText('LINESTRING(50 50, 50
 150)'),ST_GeomFromText('POLYGON((30 50, 30 150, 70 150, 70 50, 30 50))')
 )
 ));
 }}}
 the result is:
 MULTILINESTRING((50 49.9999999999999,50 50),(50 150,50 200))

 ----
 Instead if I add another digit:

 {{{
 SELECT ST_AsText(
 ST_Difference(
 ST_GeomFromText('LINESTRING(50 49.99999999999999, 50 200)'),
 ST_Intersection(ST_GeomFromText('LINESTRING(50 50, 50
 150)'),ST_GeomFromText('POLYGON((30 50, 30 150, 70 150, 70 50, 30 50))')
 )
 ));
 }}}

 the result is:
 MULTILINESTRING((50 50,50 50),(50 150,50 200))

 ----
 and if I add another digit again

 {{{
 SELECT ST_AsText(
 ST_Difference(
 ST_GeomFromText('LINESTRING(50 49.999999999999999, 50 200)'),
 ST_Intersection(ST_GeomFromText('LINESTRING(50 50, 50
 150)'),ST_GeomFromText('POLYGON((30 50, 30 150, 70 150, 70 50, 30 50))')
 )
 ));

 }}}

 the result is:
 LINESTRING(50 150,50 200)
 ----

 I guess the second result is not correct because it return a
 multiline with a point.

 I'm using debian lenny 32 bit with postgres 9.0.1 and Postgis trunk
 r6824 and geos svn r3222

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/832>
PostGIS <http://trac.osgeo.org/postgis/>
The PostGIS Trac is used for bug, enhancement & task tracking, a user and developer wiki, and a view into the subversion code repository of PostGIS project.