Changes between Version 86 and Version 87 of WKTRaster/SpecificationWorking01

Timestamp:

Dec 21, 2009, 1:37:19 PM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking01

@@ -304 +304 @@
 
 
-'''ST_Intersects(raster|geometry, raster|geometry)'''
+'''ST_Intersects(raster, 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) -> boolean
+ 
+ Variant 2: ST_Intersects(raster, raster) -> boolean
+
+ This function permform a full intersection test and proceed in three steps to determine if the raster intersects with the geometry:
+
+ 1) It first checks if the bounding box of the raster intersects with the bounding box of the geometry using the && operator. This test if very quick.
+
+ 2) If the first test returns TRUE, it checks if the geometry returned by ST_ConvexHull(raster, 'WITHNODATA') intersects with the geometry. This test is slower since it might involve the geometry shape.
+
+ 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.
+
+ Variant 2 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).
+
+ If you want to limit the intersection test to the first condition, simply use the && operator:
+
+  raster && geometry
+
+ If you want to limit the intersection test to the second condition you can write:
+
+  ST_Intersects(ST_ConvexHull(raster, 'WITHNODATA'), geometry)
+
+  '''Implementation details'''
+ 
+ This function should be implemented as a pl/pgSQL function performing the three test described one after and conditionally to the other.
+
+ It might be faster to skip test 2) if this test is not signicantly faster than test 3).
 
 '''ST_Intersection(raster|geometry, raster|geometry, ‘raster’|’geometry’)->raster/geometry'''
+
+ 
 
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