[postgis-devel] [PostGIS] #354: ST_FlipCoordinates(geometry)

[PostGIS]

#354: ST_FlipCoordinates(geometry)
--------------------------+-------------------------------------------------
  Reporter:  pramsey      |       Owner:  pramsey      
      Type:  enhancement  |      Status:  new          
  Priority:  low          |   Milestone:  PostGIS 2.0.0
 Component:  postgis      |     Version:  trunk        
Resolution:               |    Keywords:               
--------------------------+-------------------------------------------------
Comment (by kneufeld):

 Until this gets implemented in C, this could be a simple SQL function
 wrapper.

 It's been many years since I've done matrix algebra so I might not have
 this exactly right, but this does seem to work.

 {{{
 SELECT ST_AsText(ST_Affine(
  column1,
  cos(pi()/2), sin(pi()/2),
  sin(pi()/2), cos(pi()/2),
   0,          0
 ))
 FROM (VALUES
  ('POINT(4 3)'),
  ('LINESTRING(1 2, 59 34, -9 3)'),
  ('POLYGON (( 2 13, 6 12, 4 8, 2 7, 2 13 ),
             ( 4 12, 3 10, 3 9, 4 10, 4 12 ))')
 ) a;
                           st_astext
 -------------------------------------------------------------
  POINT(3 4)
  LINESTRING(2 1,34 59,3 -9)
  POLYGON((13 2,12 6,8 4,7 2,13 2),(12 4,10 3,9 3,10 4,12 4))
 (3 rows)

 }}}

 Note: anyone wishing to use [http://postgis.refractions.net/documentation/
 manual-svn/ST_Affine.html ST_Affine] to swap ordinates may need to push
 the results through [http://postgis.refractions.net/documentation/manual-
 svn/ST_SnapToGrid.html ST_SnapToGrid] since matrix computation is done on
 the coordinates.


 {{{
 SELECT ST_AsText(ST_Affine(
  'POINT(0 4)'::geometry,
  cos(pi()/2), sin(pi()/2),
  sin(pi()/2), cos(pi()/2),
   0,          0
            st_astext
 --------------------------------
  POINT(4 2.44929359829471e-016)
 (1 row)
 ));
 }}}

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/354#comment:1>
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