Changes between Version 60 and Version 61 of WKTRaster/SpecificationWorking01

Timestamp:

Dec 16, 2009, 11:05:37 AM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking01

@@ -194 +194 @@
  This function replaces ST_Raster_to_box2d() and should be used for the "raster AS box2d" cast. It should also be used instead of ST_raster_envelope when creating indexes in gdal2wktraster.py (to be tested).
 
-'''ST_Envelope(raster) -> polygon geometry''' Returns the minimum bounding box for the supplied raster, as a geometry. If the raser is rotated, the envelope is a non-rotated box enclosing the rotated raster.
+'''ST_Envelope(raster) -> polygon geometry''' Returns the minimum bounding box for the supplied raster, as a geometry. 
+
+ If the raser is rotated, the envelope is a non-rotated box enclosing the rotated raster.
 
  This function should replace the actual ST_raster_envelope() function which is wrongly named.
@@ -202 +204 @@
  By default the resulting polygon TAKES the NODATA values into account. The resulting polygon enclose only pixels having a significant value (different than the NODATA value). The ST_ConvexHull(raster, 'WITHNODATA') variant DO NOT TAKE the NODATA value into account. It generally returns a square or rectangle polygon that can be rotated or not depending on the rotation of the raster. If the raster is not rotated ST_ConvexHull(geometry, 'WITHNODATA') is (almost) equivalent to ST_Envelope(raster).
 
-'''ST_Shape(raster) -> polygon geometry'''- Returns a geometry encomparsing every pixel having a significant value (different than the NODATA value). This geometry might contain holes if some internal areas of the raster contain pixels with NODATA values.
-
-'''ST_AsPolygon(raster) -> polygon geometry set''' Returns a geometry for each 
+'''ST_Shape(raster) -> polygon geometry'''- Returns a geometry encomparsing every pixel having a significant value (different than the NODATA value).
+
+ This polygon geometry might contain holes if some internal areas of the raster contain pixels with NODATA values.
+
+'''ST_AsPolygon(raster) -> polygon geometry set''' Returns a set of geometry, one for each group of pixel having the same value.
+
+ 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.
+ 
+ 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().
+
+'''ST_AsSmoothPolygon(raster) -> polygon geometry set''' Returns a set of geometry, one for each group of pixel having the same value.
+
+ The shape of each polygon is smooted to remove stair effects.
+
 
 ST_GetBBox(raster) (not yet implemented but planned) is replaced with ST_Envelope() since there is no equivalent function in PostGIS.