[postgis-tickets] [PostGIS] #2964: ST_OffSetCurve returns EMPTY geometries and other issues

[PostGIS]

#2964: ST_OffSetCurve returns EMPTY geometries and other issues
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 Reporter:  drbullit        |       Owner:  pramsey      
     Type:  defect          |      Status:  new          
 Priority:  medium          |   Milestone:  PostGIS 2.1.5
Component:  postgis         |     Version:  2.1.x        
 Keywords:  st_offsetcurve  |  
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 First issue is that when using negative offset values, st_offsetcurve
 returns an EMPTY geometry in some cases.

 Reference geometry:
 LINESTRING(-76.941839 38.915428,-76.941883 38.915476,-76.94189 38.915497)

 Both st_astext(st_offsetcurve(geom, -15)) and
 st_astext(st_offsetcurve(geom, -1)) return LINESTRING EMPTY


 Positive offset values do not return empty geometries, but do seem to
 affect length of the geometry. I was under the assumption these result
 geometries would only be 'shifted parallelly' not see significant geometry
 changes:

 original geometry length -- st_length(geom, true) --> 4879.15614361318

 result of st_length(st_offsetcurve(geom, 1),true) -->
 168892.068090029


 SRID of original geometry is 4326

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/2964>
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