Buffering make it works. Cheers, Rémi-C
2013/12/19 Rémi Cura <[email protected]> > Hey, thanks for the answer, and nice catch ! > I'll try to simply buffer points, > then try th eother method to count > > About performance : > this is not about plpgsql or C. > I did quit the same processing when importing files of 3 millions points > to split into small 1*1*1 m cubes. > There were a lot of cubes (around 2k for 3 millions points), a lot of > points (3 millions) with a lot of attributes (around 20 flaot/double per > point), and it was around 60 sec/ file (for the data processing. Data > reading from disk was little longer). > > > For a 50x50 pixels and a few thousand points I would expect around 200ms. > > > I suspect it all boils down to current pixel access mechanism. > *Can you please confirm if there is or isn't a method to set/get several > pixels at a time?* > > Thanks anyway, > I wouldn't have found =) > > Cheers, > Rémi-C > > > 2013/12/19 Pierre Racine <[email protected]> > >> "MEAN_OF_VALUES_AT_PIXEL_CENTROID", which is the default >> ST_ExtractToRaster() method, search for geometries intersecting with the >> centroid of the pixel (a point). That's the method you use both calls to >> ExtractToRaster(). As it's almost impossible that a point intersects a >> point, this is certainly not the right method to get the value of points >> inside the pixel. A proper method would be "MEAN_VALUE_OF_POINTS" or >> "MEAN_VALUE_OF_GEOMETRIES" or "FIRST_GEOMETRY_VALUE" which are not >> implemented... >> >> I suggest you try 'COUNT_OF_POINTS' for now which will set each pixel >> value to the number of point intersecting with it. If you get it to work >> and you're satisfied with the performance I could help adding a method for >> your specific need. >> >> Can't do anything about the performance. All this is pure pl/pgsql and >> it's as fast as it can. 5 seconds to compute 2500 pixels value using SQL is >> not that bad though if you're not on the web... Otherwise you should have a >> specific C function doing exactly what you want. Expect time and $$$. >> >> Pierre >> >> >
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