Changes between Version 146 and Version 147 of WKTRaster/SpecificationWorking03

Timestamp:

07/11/11 14:12:55 (13 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking03

@@ -538 +538 @@
 
 ----
+== '''Objective FV.19 - Being able burn geometries to existing raster''' ==
+
+'''ST_BurnToRaster(rast, geometry[, value, expression, nodata1expr, nodata2expr, nodatanodataexpr]) -> raster'''
+
+ * Burn a raster to the band of an existing raster.
+ 
+ * No geoferencing metadata have to be provided since the ones of the provided raster are used.
+
+ * This function is mostly different from the ST_AsRaster(geometry) by the fact that it must provide some options to take into account the existing pixel values when burning the new value associated with the geometry.
+
+ * It should be implemented as some wrappers around ST_MapAlgebra(raster, band, ST_AsRaster(geometry, val, raster, "CROP"), 'expression', 'nodata1expr', 'nodata2expr', 'nodatanodataexpr').
+
+ * 'expression', 'nodata1expr', 'nodata2expr', 'nodatanodataexpr' are SQL expressions passed to the underlying two raster map algebra function:
+
+ -'expression' is evaluated when both pixels have a value associated with them. The default for this expression is 'LAST'.[[BR]]
+ -'nodata1expr' is evaluated when rast1 is a nodata value and rast2 has a value associated with it. The default for this expression is NULL.[[BR]]
+ -'nodata2expr' is evaluated when rast2 is a nodata value and rast1 has a value associated with it. The default for this expression is NULL.[[BR]]
+ -'nodatanodataexpr' is evaluated when both pixels are nodata values. The default for this expression is NULL.
+
+ * Here are some commonly used predefined expressions and how they materialize as the ST_Mapalgebra(rast1, rast2) expression, nodata1expr and nodata2expr, and nodatanodataexpr.
+
+ -LAST: expression = 'rast2'. This is the default ST_BurnToRaster expression.
+
+ -COUNT: expression = '2', nodata1expr = '1', nodata2expr = '1', nodatanodataexpr = '0'
+
+ -MAX: expression = 'GREATEST(rast1, rast2)' , nodata1expr = 'rast2', nodata2expr = 'rast1', nodatanodataexpr = 'NULL'
+
+ -MIN: expression = 'LEAST(rast1, rast2)' , nodata1expr = 'rast2', nodata2expr = 'rast1', nodatanodataexpr = 'NULL'
+
+ -RANGE: expression = 'ABS(rast1 - rast2)' , nodata1expr = '0', nodata2expr = '0', nodatanodataexpr = 'NULL'
+
+ -SUM: expression = 'rast1 + rast2' , nodata1expr = 'rast2', nodata2expr = 'rast1', nodatanodataexpr = 'NULL'
+
+ -MEAN: expression = '(rast1 + rast2)/2' , nodata1expr = 'rast2', nodata2expr = 'rast1', nodatanodataexpr = 'NULL'
+
+ * When expression is 'LAST' the process can be implemented with GDALRasterizeLayers since, apparently GDALRasterizeLayers do not allow other burning rules.
+
+'''ST_UnionToRaster(set of geometry[, p_expr, t_expr, f_expr]) -> raster'''
+
+ * ST_UnionToRaster is an aggregate function very similar to ST_Union(set of raster) which burn, one after the other, all the geometries of a table, or selected by a GROUP BY clause, into a unique raster.
+
+ * It is implemented as a wrapper around ST_Union(ST_AsRaster(geometry, value, raster, band, p_expression, t_expression, f_expression)) function.
+
+ * Variants
+
+ 1) ToRaster(raster, band, geometry, val)
+ 2) ToRaster(raster, band, geometry, val, p_expression)
+ 3) ToRaster(raster, band, geometry, val, p_expression, t_expression)
+ 4) ToRaster(raster, band, geometry, val, p_expression, t_expression, f_expression)
+
+----
 == '''Other functions''' ==