Changes between Version 121 and Version 122 of WKTRaster/SpecificationWorking01

Show
Ignore:
Timestamp:
04/14/10 10:48:12 (4 years ago)
Author:
pracine
Comment:

--

Legend:

Unmodified
Added
Removed
Modified
  • WKTRaster/SpecificationWorking01

    v121 v122  
    244244 This function could be roughly implemented as a SQL function looking like 'SELECT ST_Collect((ST_DumpAsPolygons(raster)).geom)'. For sure a more specialised version could be faster than ST_AsPolygon. 
    245245 
    246 '''ST_DumpAsPolygons(raster, integer) -> geomval set''' - Returns a set of "geomval" value, one for each group of pixel sharing the same value for the provided band. 
    247  
    248  This is a set-returning function (SRF). A "geomval" value is a complex type composed of a polygon geometry (one for each group of pixel sharing the same value) and the value associated with this geometry. These values are always returned as a value of type double precision. The shape of each polygon follow pixels edges. 
     246'''ST_DumpAsPolygons(raster, integer) -> geomval set''' - Returns a set of "geomval" value, one for each contiguous group of pixel sharing the same value for the provided band. 
     247 
     248 This is a set-returning function (SRF). A "geomval" value is a complex type composed of a polygon geometry (one for each contiguous group of pixel sharing the same value) and the value associated with this geometry. These values are always returned as a value of type double precision. The shape of each polygon follow pixels edges. 
    249249 
    250250 Variant 1: ST_DumpAsPolygons(raster) -> geomval set -- default to band # 1 
     
    255255  
    256256 This function is at the base of the first version of ST_Intersection which compute the intersection between a raster and a geometry. 
    257  
    258  The "CONTIGUOUS" version could be implemented by "dumping" (see geometry_dump in PostGIS) the complex polygon into separate simple polygons. 
    259257 
    260258 To avoid linking directly with PostGIS (see "Why avoid to link with PostGIS?" below) It should be implemented as a SQL wrapper around DumpAsWKTPolygons() looking something like this: