[postgis-tickets] [PostGIS] #2210: [raster]: ST_Envelope for raster that considers only data values

[PostGIS]

#2210: [raster]: ST_Envelope for raster that considers only data values
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 Reporter:  robe         |       Owner:  dustymugs    
     Type:  enhancement  |      Status:  assigned     
 Priority:  medium       |   Milestone:  PostGIS 2.1.0
Component:  raster       |     Version:  trunk        
 Keywords:               |  
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Comment(by robe):

 How about signature:

 {{{
 ST_ConvexHull(raster rast, exclude_no_data = false, band_num=NULL);
 }}}



 If band_nun is NULL then (all bands are considered as is current behavior)
 meaning the first band to hit a road block wins.

 e.g.

 Let's say you have 3 bands and for the sake of silly argument, band 1 is
 nothing but no data, but band 2 has all pixels with data, and band 3 has
 some.

 Then an ST_ConvexHull that excludes no data will return the same as
 ST_ConvexHull that includes no data -- since band 2 hits its limit first.
 In theory if there is any band that does not have a no data value you can
 return the same as current ST_ConvexHull if no bands are explicitly
 specified.

 If you specify band 3 then you get a possibly smaller rectangle than the
 original and if you specify band 1 you get an EMPTY POLYGON.

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2210#comment:5>
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