Changes between Version 82 and Version 83 of WKTRaster/SpecificationWorking01


Ignore:
Timestamp:
12/18/09 13:54:44 (15 years ago)
Author:
pracine
Comment:

Legend:

Unmodified
Added
Removed
Modified
  • TabularUnified WKTRaster/SpecificationWorking01

    v82 v83  
    237237 This function could be roughly implemented as a SQL function looking like 'SELECT ST_Collect((ST_AsPolygon(raster)).geom)'. For sure a more specialised version could be faster than ST_AsPolygon.
    238238
    239 '''ST_AsPolygon(raster) -> polygon geometry set''' - Returns a set of geometry, one for each group of pixel having the same value.
    240 
    241  This is a set-returning function (SRF). The shape of each polygon should exactly follow pixels edges.
    242 
    243  A ST_AsPolygon(raster, 'GROUP') variant should regroup every resulting polygon having the same value into complex (or multipart) polygons.
     239'''ST_AsPolygon(raster) -> geomval set''' - Returns a set of "geomval" value, one for each group of pixel having the same value.
     240
     241 This is a set-returning function (SRF). A "geomval" value is a complex type composed of a polygon geometry (one for each group of contiguous pixel of sharing same value) and the value associated with these pixels. The value associated with the group of pixel are always returned as a double precision value. The shape of each polygon follow pixels edges.
     242
     243 A ST_AsPolygon(raster, 'REGROUP') variant should regroup every resulting polygon having the same value into complex (or multipart) polygons.
    244244 
    245  This function should be used with precaution on raster with float pixel type as it could return one polygon per pixel. This kind of raster should be reclassified (using the planned ST_Reclassify(raster,...) function) before using ST_AsPolygon().
     245 This function should be used with precaution on raster with float pixel type as it could return one "geomval" (or polygon) per pixel. This kind of raster should be reclassified (using the planned ST_Reclassify(raster,...) function) before using ST_AsPolygon().
    246246
    247247 '''Implementation details'''