Changes between Version 111 and Version 112 of WKTRaster/SpecificationWorking01

Timestamp:

Feb 10, 2010, 10:30:53 AM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking01

@@ -248 +248 @@
  Variant 1: ST_AsPolygon(raster) -> geomval set -- default to band # 1
 
- Variant 2: ST_AsPolygon(raster, integer, 'CONTIGUOUS')[[BR]]
+ Variant 2: ST_AsPolygon(raster, integer, 'CONTIGUOUS')[[BR]] -- the second parameter is the raster band number
  Variant 3: ST_AsPolygon(raster, 'CONTIGUOUS') -- default to band # 1
 
@@ -258 +258 @@
  
  This function is at the base of the first version of ST_Intersection which compute the intersection between a raster and a geometry.
+
+ The "CONTIGUOUS" version could be implemented by "dumping" (see geometry_dump in PostGIS) the complex polygon into separate simple polygons.
 
  To avoid linking directly with PostGIS (see "Why avoid to link with PostGIS?" below) It should be implemented as a SQL wrapper around ST_AsWKTPolygon() looking something like this:
@@ -276 +278 @@
 '''ST_AsWKTPolygon(raster, integer) -> wktgeomval set''' - Returns a set of "geomval" value, one for each group of pixel sharing the same value for the provided band.
 
- This is a set-returning function (SRF). A "wktgeomval " value is a complex type composed of a the wkt representation of a geometry (one for each group of pixel sharing the same value) and the value associated with this geometry. These values are always returned as a value of type double precision. The shape of each polygon follow pixels edges.
+ Variant 1: ST_AsWKTPolygon(raster) -> wktgeomval set -- default to band # 1
+
+ This is a set-returning function (SRF). A "wktgeomval " value is a complex type composed of a the wkt representation of a geometry (one for each group of pixel sharing the same value) and the value associated with this geometry. These values are always returned as a value of type double precision. The shape of each polygon follow pixels edges. Areas with NODATA values are not included in the resulting set.
 
  This function should be used with precaution on raster with float pixel type as it could return one "geomval" (or polygon) per pixel. This kind of raster should be reclassified (using the planned ST_Reclassify(raster,...) function) before using ST_AsWKTPolygon().
@@ -289 +293 @@
 
 
-'''ST_Intersects(raster, integer, geometry) -> boolean''' - Returns TRUE if the geometry and the raster "spatially intersect" - (share any portion of space) and FALSE if they don't (they are Disjoint).
+'''ST_Intersects(raster, integer, geometry) -> boolean''' - Returns TRUE if the geometry and the raster "spatially intersect" - (share any portion of space) and FALSE if they don't (they are disjoint). 
 
  Variant 1: ST_Intersects(geometry, raster, integer) -> boolean -- the third parameter is the raster band number
@@ -305 +309 @@
  2) If the first test returns TRUE, it checks if the geometry returned by ST_ConvexHull(raster) intersects with the geometry.
 
- 3) If the second test returns TRUE, it checks if the geometry returned by ST_Shape(raster) intersects with the geometry. This test is slower since it involve the computation of the raster shape and it might involve the geometry shape.
+ 3) If the second test returns TRUE, it checks if the geometry returned by ST_Shape(raster, integer) intersects with the geometry. This test is slower since it involve the computation of the raster shape and it might involve the geometry shape. This test takes NODATA values into account. i.e. A geometry intersecting only with a NODATA value area of a raster is NOT actually not intersecting with this raster. This behavior may be controled by limiting the test to certain conditions as stated below. 
 
  Variant 4 proceeds in a very similar way except that convex hulls of both rasters are computed and compared in step 2) and both shape of raster are computed and compared in step 3).