[raster] ST_Clip fails when polygon barely intersects with raster

[yosukesabai]

It would be better if this returns one pixel, or nothing at all. Currently it throws ERROR and I found hard to handle the error in PG/SQL.

SELECT ST_Summary(
  ST_Clip(
    ST_AddBand(
      ST_MakeEmptyRaster(16, 16, 0, 0, 1, 1, 0, 0),
      ARRAY[
        ROW(1, '8BUI'::text, 0, 255),
        ROW(2, '8BUI'::text, 0, 255),
        ROW(3, '8BUI'::text, 0, 255)
      ]::addbandarg[]
    )
    -- this works
    --, ST_GeomFromText('POLYGON((15.999999 15.999999, 15.999999 17, 17 17, 17 15.999999, 15.999999 15.999999))')
    -- this fails
    , ST_GeomFromText('POLYGON((15.9999999 15.9999999, 15.9999999 17, 17 17, 17 15.9999999, 15.9999999 15.9999999))')
  )
);

[robe]

In 15456:

Change ST_Clip from Error to Notice when ST_Clip can compute no band
References #3730 for PostGIS 2.4

[robe]

I changed this from Erroring to just providing a NOTICE and returning NULL as it was before.

I notice that when the geometry doesn't intersect the raster, it returns an empty raster, but I'm not sure under what other conditions clip can not compute a raster, so I left it as returning null.

We might want to revisit this in PostGIS 2.4 to see if we can revise ST_Clip to have an option of returning a single pixel if there is a partial pixel overlap. I think right now if there is a partial pixel overlap, it doesn't return the pixel.

[robe]

fixed at r15457 for PostGIS 2.3.3