[postgis-users] point to raster conversion

[Rémi Cura]

Buffering make it works.

Cheers,
Rémi-C


2013/12/19 Rémi Cura <remi.cura at gmail.com>

> 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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