Changes between Version 82 and Version 83 of WKTRaster/SpecificationWorking01

Timestamp:

Dec 18, 2009, 1:54:44 PM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking01

@@ -237 +237 @@
  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.
 
-'''ST_AsPolygon(raster) -> polygon geometry set''' - Returns a set of geometry, one for each group of pixel having the same value.
-
- This is a set-returning function (SRF). The shape of each polygon should exactly follow pixels edges.
-
- A ST_AsPolygon(raster, 'GROUP') variant should regroup every resulting polygon having the same value into complex (or multipart) polygons.
+'''ST_AsPolygon(raster) -> geomval set''' - Returns a set of "geomval" value, one for each group of pixel having the same value.
+
+ 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.
+
+ A ST_AsPolygon(raster, 'REGROUP') variant should regroup every resulting polygon having the same value into complex (or multipart) polygons.
  
- 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().
+ 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().
 
  '''Implementation details'''