Changes between Version 91 and Version 92 of WKTRasterTutorial01

Timestamp:

Aug 22, 2010, 6:54:31 PM (14 years ago)

Author:

tylere

Comment:

minor grammar correction

WKTRasterTutorial01

@@ -349 +349 @@
 As its geometry/geometry sister, ST_Intersects(geometry, raster, band) returns TRUE if the withvalue area of a raster or a raster tile intersects a geometry and ST_Intersection(geometry, raster, band) returns the geometry/value set of geometries representing the intersection between the geometry and each polygonized group of pixel sharing a same value from the raster and its associated value. It is important to note here that ST_Intersects and ST_Intersection take the nodata value into account. That means if a polygon fall entirely in a nodata value area of a raster, ST_Intersects return FALSE and ST_Intersection returns an EMPTY GEOMETRY. This is a very important raster analysis feature.
 
-The second version of the query takes only 7.4 minutes to complete. Almost half the time spent by the first one... This little increase in complexity certainly worths the gain in performance. The size of the tiles has also a major effect here. If we restart the whole process with 200 pixels x 200 pixels tiles the intersection operation takes 47 minutes. 100 pixels x 100 pixels: 17 minutes... 30 pixels x 30 pixels: 5 minutes. On the other side, more tiles there is to write in the sql file, longer the loading process. You choose... Smaller tiles is generally a better choice.
+The second version of the query takes only 7.4 minutes to complete. Almost half the time spent by the first one... This little increase in complexity is certainly worth the gain in performance. The size of the tiles has also a major effect here. If we restart the whole process with 200 pixels x 200 pixels tiles the intersection operation takes 47 minutes. 100 pixels x 100 pixels: 17 minutes... 30 pixels x 30 pixels: 5 minutes. On the other side, more tiles there is to write in the sql file, longer the loading process. You choose... Smaller tiles is generally a better choice.
 
 [[Image(WKTRasterViewOfIntersectionResult.gif, align=right, 50%)]]