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

[Bborie Park]

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
>>>
>>> _______________________________________________
>>> postgis-users mailing list
>>> postgis-users at lists.osgeo.org
>>> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
>>>
>>
>>
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>>
>
>
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