[postgis-devel] [PostGIS] #1673: [raster] Add a note on ST_Union(raster) slowness

[PostGIS]

#1673: [raster] Add a note on ST_Union(raster) slowness
---------------------------+------------------------------------------------
 Reporter:  pracine        |       Owner:  robe         
     Type:  defect         |      Status:  new          
 Priority:  medium         |   Milestone:  PostGIS 2.0.0
Component:  documentation  |     Version:  trunk        
 Keywords:                 |  
---------------------------+------------------------------------------------

Comment(by robe):

 done at r9508.  I also put in a note to use ST_Clip first and then union.

 I discovered when creating my report images that if I clip the rasters to
 my polygon area of interest and then union the raster shards, it's way
 faster than trying to union the intersecting rasters and then clipping to
 my geometry of interest.

 For example for my o_2 the difference was 3.5 seconds vs. 8 seconds if you
 (clip + union) vs. (union + clip).

 For the hi-res, the timing was more starkling -- something like 9 seconds
 vs. 30 seconds.

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/1673#comment:3>
PostGIS <http://trac.osgeo.org/postgis/>
The PostGIS Trac is used for bug, enhancement & task tracking, a user and developer wiki, and a view into the subversion code repository of PostGIS project.