Changes between Version 121 and Version 122 of WKTRaster/SpecificationWorking01
 Timestamp:
 04/14/10 10:48:12 (4 years ago)
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WKTRaster/SpecificationWorking01
v121 v122 244 244 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. 245 245 246 '''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 setreturning 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 setreturning 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. 249 249 250 250 Variant 1: ST_DumpAsPolygons(raster) > geomval set  default to band # 1 … … 255 255 256 256 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.259 257 260 258 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: