[postgis-tickets] [PostGIS] #2249: [raster] Implement ST_MakeEmptyCoverage

[PostGIS]

#2249: [raster] Implement ST_MakeEmptyCoverage
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 Reporter:  dzwarg       |       Owner:  dzwarg       
     Type:  enhancement  |      Status:  assigned     
 Priority:  medium       |   Milestone:  PostGIS 2.2.0
Component:  raster       |     Version:  trunk        
 Keywords:  raster       |  
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Comment(by pracine):

 Replying to [comment:5 strk]:
 > I've taken a look at the function signature in the latest patch and got
 a bit scared :)
 > I imagine a coverage creation as two steps:
 >
 >  1. Creation of the table that would represent the coverage
 configuration
 >  2. Population of the coverage
 >
 > The first step could be similar to AddRasterColumn, that is it only
 creates a structure,
 > w/out inserting the data.
 >
 > The way I'd call such a coverage-creation function would be by passing
 it:
 >
 > Mandatory:
 >
 >  1. The spatial extent to be covered by the coverage
 >  2. The pixel size in geographical units (the scale)
 >
 > Optional:
 >
 >  3. SRID. Unconstrained if not given. [ok, maybe this could be
 mandatory]
 >  4. The max size of coverage tiles in pixels. Unconstrained if not
 given.
 >
 > I see this function instead creates a whole set of empty tiles,
 > which is possibly a big waste of time as you probably want to later
 modify
 > those tiles to have actual data in them...
 >
 > Also for a big coverage it could be very easy to end up out of memory.

 ST_MakeEmptyCoverage() should create EMPTY rasters tiles, thus having no
 bands and hence almost no data. It is useful for any query that want a set
 of reference tiles to recreate a raster coverage from an existing one or
 from a vector coverage (rasterizing). You use, for example, to create on
 the fly an empty raster table in the FROM geomtable, (SELECT
 ST_MakeEmptyCoverage() rast) that is used only as reference by function in
 the SELECT. Many functions have a reference raster as parameter from which
 they borrow alignment information.

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2249#comment:8>
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