= Determine Cardinal Direction =

See [http://en.wikipedia.org/wiki/Cardinal_direction Wikipedia] for a description for cardinal direction.

{{{
CREATE OR REPLACE FUNCTION ST_CardinalDirection(azimuth float8) RETURNS character varying AS
$BODY$SELECT CASE
  WHEN $1 < 0.0 THEN 'less than 0'
  WHEN degrees($1) < 22.5 THEN 'N'
  WHEN degrees($1) < 67.5 THEN 'NE'
  WHEN degrees($1) < 112.5 THEN 'E'
  WHEN degrees($1) < 157.5 THEN 'SE'
  WHEN degrees($1) < 202.5 THEN 'S'
  WHEN degrees($1) < 247.5 THEN 'SW'
  WHEN degrees($1) < 292.5 THEN 'W'
  WHEN degrees($1) < 337.5 THEN 'NW'
  WHEN degrees($1) <= 360.0 THEN 'N'
END;$BODY$ LANGUAGE sql IMMUTABLE COST 100;
COMMENT ON FUNCTION ST_CardinalDirection(float8) IS 'input azimuth in radians; returns N, NW, W, SW, S, SE, E, or NE';
}}}

Example:
{{{
SELECT
  degrees(ST_Azimuth(origin, pt)) AS azimuth_in_degrees,
  ST_CardinalDirection(ST_Azimuth(origin, pt))
FROM (
  SELECT
    'POINT(0 0)'::geometry AS origin,
    ST_MakePoint(cos(radians(x)), sin(radians(x))) AS pt
  FROM generate_series(0, 365, 15) AS x
) AS f;

  azimuth_in_degrees   | st_cardinaldirection
-----------------------+----------------------
                    90 | E
                    75 | E
                    60 | NE
                    45 | NE
                    30 | NE
                    15 | N
 3.50835464926744e-015 | N
                   345 | N
                   330 | NW
                   315 | NW
                   300 | NW
                   285 | W
                   270 | W
                   255 | W
                   240 | SW
                   225 | SW
                   210 | SW
                   195 | S
                   180 | S
                   165 | S
                   150 | SE
                   135 | SE
                   120 | SE
                   105 | E
                    90 | E
(25 rows)
}}}