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

[Jean Marchal]

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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