[postgis-tickets] [PostGIS] #2645: ST_LineInterpolatePoint incorrect output for vertical line

[PostGIS]

#2645: ST_LineInterpolatePoint incorrect output for vertical line
------------------------------+---------------------------------------------
 Reporter:  bencaradocdavies  |       Owner:  pramsey      
     Type:  defect            |      Status:  new          
 Priority:  high              |   Milestone:  PostGIS 2.1.2
Component:  postgis           |     Version:  2.1.x        
 Keywords:                    |  
------------------------------+---------------------------------------------
 For a vertical line (a single segment varying only in Z),
 ST_LineInterpolatePoint incorrectly outputs the the last point for any
 fraction greater than zero:
 {{{
 $ select st_asewkt(st_lineinterpolatepoint(st_geomfromewkt('LINESTRING(0 0
 0, 0 0 1)'), 0.5));
   st_asewkt
 --------------
  POINT(0 0 1)
 (1 row)
 }}}

 The output in this case should be:
 {{{
  POINT(0 0 0.5)
 }}}

 Non-vertical lines appear to be interpolated correctly:
 {{{
 $ select st_asewkt(st_lineinterpolatepoint(st_geomfromewkt('LINESTRING(0 0
 0, 1 0 1)'), 0.5));
     st_asewkt
 ------------------
  POINT(0.5 0 0.5)
 (1 row)
 $ select st_asewkt(st_lineinterpolatepoint(st_geomfromewkt('LINESTRING(0 0
 0, 0 1 1)'), 0.5));
     st_asewkt
 ------------------
  POINT(0 0.5 0.5)
 (1 row)
 }}}

 Seen on CentOS 6.5 x86_64:
 {{{
 postgresql93.x86_64 9.3.2-1PGDG.rhel6
 postgis2_93.x86_64 2.1.1-1.rhel6
 }}}

 And on Debian sid amd64:
 {{{
 postgresql-9.3 9.3.2-1 amd64
 postgis 2.1.1-5 amd64
 }}}

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2645>
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