[postgis-users] [Raster] Finding pixels intersecting an extent (polygon)

[Jean Marchal]

It worked! Thanks a lot!

Jean

2015-02-05 15:18 GMT-08:00 Bborie Park <dustymugs at gmail.com>:

> Try something like:
>
> WITH foo AS (
> SELECT
> ST_AsRaster(
> ST_GeomFromText('POLYGON ((-52.54178994517749 46.99199259385565,
> -52.54178994517749 46.996897959881, -52.53436080387823 46.996897959881,
> -52.53436080387823 46.99199259385565, -52.54178994517749
> 46.99199259385565))', 4269),
> rast,
> '8BUI',
> touched := True
> ) AS rast
> FROM elev
> LIMIT 1
> )
> SELECT
> ST_Intersection(
> elev.rast,
> foo.rast
> ) AS rast
> FROM elev
> JOIN foo
> ON ST_Intersects(elev.rast, foo.rast)
>
> The idea is to explicitly convert the geometry into a raster using one of
> the elev rasters as a reference. The "touched := True" slightly changes the
> behavior of the rasterization.
>
> From the docs:
>
> The optional touched parameter defaults to false and maps to the GDAL
> ALL_TOUCHED rasterization option, which determines if pixels touched by
> lines or polygons will be burned.
>
> On Thu, Feb 5, 2015 at 2:45 PM, Jean Marchal <jean.d.marchal at gmail.com>
> wrote:
>
>> Bborie,
>>
>> I am running PostGIS 2.1.5. Here is the output of the
>> postgis_full_version():
>>
>> "POSTGIS="2.1.5 r13152" GEOS="3.3.3-CAPI-1.7.4" PROJ="Rel. 4.7.1, 23
>> September 2009" GDAL="GDAL 1.9.0, released 2011/12/29" LIBXML="2.8.0"
>> LIBJSON="UNKNOWN" RASTER"
>>
>> My query looks like this:
>>
>> SELECT ST_Intersection(ST_GeomFromText('POLYGON ((-52.54178994517749
>> 46.99199259385565, -52.54178994517749 46.996897959881, -52.53436080387823
>> 46.996897959881, -52.53436080387823 46.99199259385565, -52.54178994517749
>> 46.99199259385565))', 4269), rast) as rast
>> FROM elev
>>
>> David,
>>
>> This query does not returns all the polygons that intersect my polygon. I
>> think it returns only those where the centroid is inside the polygon or is
>> it covered based? (like 50% of the pixel intersect with the polygon).
>>
>> Thanks for your rapid answers!
>>
>> Jean
>>
>> 2015-02-05 14:31 GMT-08:00 David Haynes <haynesd2 at gmail.com>:
>>
>> select ST_Clip(r.rast,p.geom) as rast
>>> from polygon p inner join raster r on ST_intersects(r.rast, p.geom)
>>>
>>> This returns a raster which has all pixels inside the polygon
>>>
>>> On Thu, Feb 5, 2015 at 4:05 PM, Jean Marchal <jean.d.marchal at gmail.com>
>>> wrote:
>>>
>>>> Hi list,
>>>>
>>>> I am trying to return all the pixels in a raster that intersect (not
>>>> just touch) an extent (say a rectangle). I tried ST_Clip and
>>>> ST_Intersection(raster, geom) but they don't return all the pixels that
>>>> intersect my extent polygon. Do I have to vectorize the raster first using
>>>> ST_PixelAsPolygons or there is a better / more efficient way to proceed?
>>>>
>>>> Ultimately the goal is to fetch the resulting raster in R.
>>>>
>>>> Thanks,
>>>>
>>>> Jean
>>>>
>>>> _______________________________________________
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>>>>
>>>
>>>
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>>
>>
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>
>
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