[postgis-users] point to raster conversion

[Rémi Cura]

QGis 2.0.1.
I tried as well to convert to UINT16
no sucess


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

> Is there a special trick to display the raster in QGIS?
> I do
> db manage/right click on the raster table/add to canvas
> Seems like there is nothing in it afterward.
>
> Thanks again,
>
> Rémi-C
>
>
> 2013/12/19 Rémi Cura <remi.cura at gmail.com>
>
>> 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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