[postgis-users] point to raster conversion

[Rémi Cura]

For the record :
when outputting the image to disk then loading it into postgis, image shows
fine (band 1 and band2)

When 'add canvas' on the image in QGIS, a nex layer is created, but empty.

Do you know other way to do it?

Cheers,

Rémi-C


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

> 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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