ST_PixelAsPolygon — 指定した行と列のピクセルの境界となるジオメトリを返します。
geometry ST_PixelAsPolygon(raster rast, integer columnx, integer rowy);
-- get raster pixel polygon
SELECT i,j, ST_AsText(ST_PixelAsPolygon(foo.rast, i,j)) As b1pgeom
FROM dummy_rast As foo
CROSS JOIN generate_series(1,2) As i
CROSS JOIN generate_series(1,1) As j
WHERE rid=2;
i | j | b1pgeom
---+---+-----------------------------------------------------------------------------
1 | 1 | POLYGON((3427927.75 5793244,3427927.8 5793244,3427927.8 5793243.95,...
2 | 1 | POLYGON((3427927.8 5793244,3427927.85 5793244,3427927.85 5793243.95, ..