Changes between Version 39 and Version 40 of WKTRaster/SpecificationWorking02

Timestamp:

Sep 21, 2010, 8:14:07 AM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking02

@@ -37 +37 @@
  Returns a one band raster which pixel values are the mathematical expression of another raster band.
 
- The expression is any PostgreSQL valid expression returning a number. This expression can contain any user-defined function. In the one raster version of ST_MapAlgebra, the value of the current pixel is expressed in the expression by "rast". E.g. 'cos(rast)' or 'rast / 2'
+ The expression is any PostgreSQL valid expression returning a number. This expression can contain conditional expressions like CASE or any user-defined function. In the one raster version of ST_MapAlgebra, the value of the current pixel is expressed in the expression by "rast". E.g. 'cos(rast)' or 'rast / 2'
 
  An extra nodata value expression, applying only to nodata values pixel, can be provided.
@@ -73 +73 @@
 
  Only the first variant should be implemented in C. Others are pl/pgSQL variants. The C implementation should follow the plpgsql script of the one raster version of ST_MapAlgebra implemented at the top of http://trac.osgeo.org/postgis/browser/spike/wktraster/scripts/plpgsql/st_mapalgebra.sql
+
+ Optimizations should be implemented in many situations:
+
+ -When the raster is only no data values (tested with ST_BandIsNoDataValue() to be implemented)
+
+ -When the expression resume to the provided raster 'rast'.
 
  Specifications for the two rasters version of ST_MapAlgebra are descibed in Objective 2.0.03.