Changes between Version 83 and Version 84 of WKTRasterTutorial01


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Timestamp:
06/29/10 14:18:59 (14 years ago)
Author:
pracine
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  • WKTRasterTutorial01

    v83 v84  
    314314== Intersecting the caribou buffers with the elevation rasters ==
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    316 [[Image(WKTRasterViewOfIntersectionResult.gif, align=right, 50%)]]
    317316Our two coverages are now ready to be intersected. We will use the st_intersection() function and st_intersects() operator which operates directly on raster and geometries by vectorizing only the necessary part of the raster before doing the intersection and is one of the main feature of PostGIS WKT Raster: 
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    … …  
    344343This version takes only 7.4 minutes. Almost half the time spent by the preceding 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.
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     345[[Image(WKTRasterViewOfIntersectionResult.gif, align=right, 50%)]]
    346346Once again you can visualise the result of the query by doing this query in OpenJUMP (you might have to increase RAM allowed to OpenJUMP by changing "-Xmx256M" to "-Xmx1024M" in "OpenJUMPInstallPath/bin/openjump.bat"):
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