Changes between Version 69 and Version 70 of WKTRaster/SpecificationWorking01

Timestamp:

12/16/09 13:47:36 (15 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking01

@@ -196 +196 @@
  The only difference with ST_Envelope(raster) is that ST_Box2D(raster) returns a BOX2D, not a geometry.
 
+ '''Implementation details'''
+
  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).
 
@@ -219 +221 @@
  '''Implementation details'''
 
- The first variant (taking NODATA values into account) ST_ConvexHull(raster) could be roughly implemented with a SQL or PL/pgSQL function looking like 'SELECT ST_ConvexHull(ST_Shape(raster))'. For sure computing only the external edge (without considering eventual holes like ST_Shape() does) should be faster. This imply writing the equivalent of a more simple version of ST_Shape.
+ The first variant (taking NODATA values into account) ST_ConvexHull(raster) could be roughly implemented as a SQL or PL/pgSQL function looking like 'SELECT ST_ConvexHull(ST_Shape(raster))'. For sure computing only the external edge (without considering eventual holes like ST_Shape() does) should be faster. This imply writing the equivalent of a more simple version of ST_Shape.
 
  The second variant (not taking NODATA values into account) is actually already implemented by the ST_raster_envelope() function which is wrongly named. There is also a ticket (#348) related to this function: http://trac.osgeo.org/postgis/ticket/348
@@ -226 +228 @@
 
  This polygon geometry might contain holes if some internal areas of the raster contain pixels with NODATA values. By opposition ST_ConvexHull(raster) never contains holes.
+
+  '''Implementation details'''
+
+ This function could be roughly implemented as a SQL or PL/pgSQL function looking like 'SELECT ST_Collect(ST_AsPolygon(raster))'. 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.
@@ -235 +241 @@
  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().
 
+ '''Implementation details'''
+ 
  This function is at the base of the first version of ST_Intersection which compute the intersection between a raster and a geometry.