ST_Covers may have bug

[petermj]

The following code produces (for me) unexpected results.

I have a large and a small tile (square polygon), and I believe the large should cover the small, but as a geography is does not, and as a geometry it does?

The tiles share a corner point, and the neighbouring corners share either longitude or latitude.

SELECT
ST_Covers(large.tile, small.tile),
ST_Covers(large.tile::geography, small.tile::geography)
FROM
	(SELECT 'POLYGON((-3.34216155333235 55.3991017765333,-3.34058316886567 55.3991017765333,-3.34058316886567 55.4,-3.34216155333235 55.4,-3.34216155333235 55.3991017765333))'::geometry as tile) as large,
	(SELECT 'POLYGON((-3.34216155333235 55.3999101776593,-3.34200371488568 55.3999101776593,-3.34200371488568 55.4,-3.34216155333235 55.4,-3.34216155333235 55.3999101776593))'::geometry as tile) as small
                 
;

I'm happy to be told my knowledge of GIS is incomplete and this is a standard newbie error, but it felt wrong to my mind….?

[petermj]

Sorry, I forgot to add I get the answer:

true, false

[pramsey]

Does this help?

​https://www.youtube.com/watch?v=GSuZP89UdGs&t=15m3s

[petermj]

Thank you very much I was suspecting this as much.