Changes between Version 133 and Version 134 of WKTRaster/SpecificationWorking03

Timestamp:

Jul 8, 2011, 9:01:26 AM (13 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking03

@@ -141 +141 @@
 
  
- '''Open question'''
+ '''Open questions'''
 
  PR: Shoud we return one raster per raster/geometry couple or split the raster into as many small rasters as there are areas sharing a same value? The second behavior seems more coherent with the present behavior of ST_Intersection(raster, geometry) -> geometry even if this would produce tons of small two bands rasters.
@@ -228 +228 @@
 '''Details for 5) to 8) Two rasters versions'''
 
- * A simple PL/pgSQL prototype of the two raster version of ST_MapAlgebra() exists in http://trac.osgeo.org/postgis/browser/trunk/raster/scripts/plpgsql/st_mapalgebra.sql. This version iterates over every pixel of the unionized extent of two rasters even if there are large areas where both rasters are absent and hence are interpreted as nodata values. An optimized prototype, trying to set those large nodata areas as well as areas where only one raster is present (this is the case when unioning two contiguous non-overlapping rasters) as a block (not pixel by pixel) using ST_SetValues() described in [http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking02 Objective 2.0.05] is still in development. See http://trac.osgeo.org/postgis/browser/trunk/raster/scripts/plpgsql/st_mapalgebra_optimized.sql The idea is to set large areas of the resulting raster when possible using a process more similar to memcpy than by computing one pixel value at a time.
-
- * Both rasters must have the same SRID. If not, ST_MapAlgebra should return an error: "ERROR:  Operation on two geometries with different SRIDs"
+ * A simple PL/pgSQL prototype of the two raster version of ST_MapAlgebra() exists in http://trac.osgeo.org/postgis/browser/trunk/raster/scripts/plpgsql/st_mapalgebra.sql. This version iterates over every pixel of the unionized extent of two rasters even if there are large areas where both rasters are absent and hence are interpreted as nodata values.
+
+ * the prototype of an optimized version, trying to set those large nodata areas as well as areas where only one raster is present (this is the case when unioning two contiguous non-overlapping rasters) as a block (not pixel by pixel) is still in development. See http://trac.osgeo.org/postgis/browser/trunk/raster/scripts/plpgsql/st_mapalgebra_optimized.sql The idea is to set blocks of the resulting raster using ST_SetValues() (described in [http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking02 Objective 2.0.05]) instead of processing one pixel at a time. This is somewhat similar to setting a large block of memory with memcpy() or memset() rather than setting a buffer one value at a time. The resulting raster is divided into rectangular block with the _MapAlgebraParts() function.
+
+ * Both rasters must have the same SRID. If not, ST_MapAlgebra() should return an error: "ERROR:  Operation on two geometries with different SRIDs"
 
  * Both raster must be aligned. This is determined using the ST_SameAlignment() function described below. If a resampling is necessary they use the planned ST_Resample() function to resample the second raster to the first one before processing (or the first to the second if an optional parameter is provided). If ST_Resample() is not yet implemented when these functions are implemented, just return an error message: "ERROR:  MapAlgebra on rasters with different alignment not yet implemented."