[postgis-users] point to raster conversion

[Rémi Cura]

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 <Pierre.Racine at sbf.ulaval.ca>

> "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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