[postgis-devel] [PostGIS] #2024: raster: ST_Union is buggy

[PostGIS]

#2024: raster: ST_Union is buggy
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 Reporter:  robe     |       Owner:  dustymugs    
     Type:  defect   |      Status:  new          
 Priority:  blocker  |   Milestone:  PostGIS 2.1.0
Component:  raster   |     Version:  trunk        
 Keywords:           |  
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Comment(by robe):

 dustymugs,

 I found a performance issue.  I thought I was imaging things in my test
 here when I was noticing the phenomenon:
 http://www.bostongis.com/blog/index.php?/archives/198-Waiting-for-
 PostGIS-2.1-Faster-Raster-Union.html

  that 2.1 speed wasn't changing with clipping and yet 2.0 was which is the
 hack I use to make 2.0 work faster.

 It seems to me that 2.1.0 is computing over no data values. So I have
 concocted a more ridiculous test to highlight the issue.  One in which
 PostGIS 2.0 trumps 2.1.0.
 the result looks same in both so not sure if its the union or the clipping
 that is at issue.


 -- clip union 2.0 wins
 -- On 2.1.0SVN, 11,415 ms (on PostGIS 2.0 this takes 6,130ms)
 {{{
 SELECT ST_AddBand(NULL,ARRAY[ST_Union(rast,1), ST_Union(rast,2),
 ST_Union(rast,3) ]) , count(*)
 FROM (SELECT  ST_Clip(rast,geom) As rast
         FROM test_100_100
            CROSS JOIN ST_Buffer(ST_GeomFromText('LINESTRING(231200
 887025,231247 888240)',26986),0.1) As geom
 WHERE ST_Intersects(rast,  geom ) ) As foo;
 }}}


 -- no clip, 2.1.0 doesn't exhibit much speed difference between clip and
 non-clip
 -- On 2.1.0SVN, 12,555ms (on PostGIS 2.0 takes 25,814ms)
 {{{
 SELECT ST_AddBand(NULL,ARRAY[ST_Union(rast,1), ST_Union(rast,2),
 ST_Union(rast,3) ]) , count(*)
 FROM (SELECT rast
         FROM test_100_100
            CROSS JOIN ST_Buffer(ST_GeomFromText('LINESTRING(231200
 887025,231247 888240)',26986),0.1) As geom
 WHERE ST_Intersects(rast,  geom ) ) As foo;
 }}}

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2024#comment:12>
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