[postgis-tickets] [PostGIS] #4765: ST_ClipByBox2D: Incorrect clipping of lines

[PostGIS]

#4765: ST_ClipByBox2D: Incorrect clipping of lines
------------------------+---------------------------
 Reporter:  Algunenano  |      Owner:  pramsey
     Type:  defect      |     Status:  new
 Priority:  medium      |  Milestone:  PostGIS 3.0.3
Component:  postgis     |    Version:  master
 Keywords:              |
------------------------+---------------------------
 It seems there is some kind of bug when clipping lines that are around the
 borders of the bbox in ST_ClipByBox2D.

 Query:
 {{{
 WITH geom AS
 (
     SELECT 'LINESTRING(0 0,0 10, 10 10,1 1)'::geometry as geom
     UNION ALL
     SELECT 'LINESTRING(0 0, 0 15, 15 15, 1 1)'::geometry as geom
 ),
 box AS
 (
     SELECT ST_MakeEnvelope(0,0,10,10) AS box
 )
 SELECT
     ST_AsText(geom) as geom,
     ST_AsText(box::box2d) as box,
     ST_AsText(ST_ClipByBox2D(geom, box)) as clip,
     ST_AsText(ST_Intersection(geom, box)) as intersection
 FROM geom, box
 }}}

 Output:
 {{{
               geom              |                box                 |
 clip              |                     intersection
 --------------------------------+------------------------------------+--------------------------------+------------------------------------------------------
  LINESTRING(0 0,0 10,10 10,1 1) | POLYGON((0 0,0 10,10 10,10 0,0 0)) |
 LINESTRING(0 0,0 10,10 10,1 1) | MULTILINESTRING((0 0,0 10),(0 10,10
 10),(10 10,1 1))
  LINESTRING(0 0,0 15,15 15,1 1) | POLYGON((0 0,0 10,10 10,10 0,0 0)) |
 LINESTRING(10 10,1 1)          | MULTILINESTRING((0 0,0 10),(10 10,1 1))
 (2 rows)
 }}}

 In the first case things look normal, both when you clip using
 ST_Intersect or ST_ClipByBox2D, but in the second case the  ST_ClipByBox2D
 output is clearly wrong as it's missing a whole lien, while
 ST_Intersection is returning a valid value.

 I haven't reproduced the issue with polygons, just lines.


 It's likely a GEOS issue, but I haven't tried to isolate it yet to report
 it there if necessary. Tested with Postgis 3.0 and master, GEOS 3.8.2 and
 master (with and without overlayNG).

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4765>
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