Changes between Version 88 and Version 89 of WKTRaster/SpecificationWorking01

Timestamp:

Dec 21, 2009, 2:06:12 PM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/SpecificationWorking01

@@ -320 +320 @@
  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:
+ If you want to limit the intersection test to the first condition, simply use the && operator. The raster and the geometry will be casted to their respective bounding box (box2d objects):
 
   raster && geometry
@@ -334 +334 @@
  It might be faster to skip test 2) if this test is not signicantly faster than test 3).
 
-'''ST_Intersection(raster, geometry) -> geometry'''
-
- Variant 1: ST_Intersection(geometry, raster) -> geometry
+'''ST_Intersection(raster, geometry) -> geometry''' - Returns a geometry that represents the shared portion of the geometry and the raster. 
+
+ Variant 1: 
+
+  ST_Intersection(geometry, raster) -> geometry
 
  Variant 2 & 3: 
@@ -350 +352 @@
   ST_Intersection(raster, raster, 'geometry') -> geometry
 
- 
+ Returns a geometry that represents the point set intersection of the geometry and the raster. The raster is first polygonised using ST_AsPolygon(raster) and ST_Intersection(geometry, geometry) is then performed between the provided geometry and all the geometries resulting from the polygonisation of the raster.
+
+ If the geometries do not share any space (are disjoint), then an empty geometry collection is returned.
+
+ ST_Intersection in conjunction with ST_Intersects is very useful for clipping geometries such as in bounding box, buffer, region queries where you only want to return that portion of a geometry that sits in a country or region of interest.
+
+ If you only want to compute the intersection between the convex hull of the raster without polygonising it to group of contiguous pixels sharing a common value, do:
+
+  ST_Intersection(ST_ConvexHull(raster, 'WITHNODATA'), geometry)
+
+ If you only want to compute the intersection between the shape of the raster without polygonising it to group of contiguous pixels sharing a common value, do:
+
+ ST_Intersection(ST_Shape(raster), geometry)
+
+ '''Implementation details'''
+
+ This function should be implemented as a pl/pgSQL function (possibly only a SQL function) performing the intersection between the provided geometry and the table generated by ST_AsPolygon(raster).
+
+
 
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