MySQL offers ENVELOPE() to find the minimum bounding rectangle of a geometric object.

The result is a polygon with four segments, defined by five points. It took me a while to make sense of it, partially because the only documentation that I’ve run across so far for POLYGON() syntax is in the ENVELOPE() function mentioned above. I also had to draw a picture to think it through.

They write this: POLYGON(( MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY )), I think this (in pseudocode-ish form): POLYGON(( $point_a, $point_b, $point_c, $point_d, $point_a )), with the $point_s corresponding to the diagram.

It’s MySQL spatial data week here, though I am spreading out the posts to, um, ease the pain (or boredom). Anyway, here are some commands/functions I don’t want to forget about later:

Start with an existing table called geometry, add a spatial column and index it:

ALTER TABLE geometry ADD coord POINT NOT NULL;
CREATE SPATIAL INDEX coord ON geometry (coord);

Insert some data; think in terms of POINT(X Y) or POINT(lat lon):

INSERT INTO geometry (coord) VALUES( GeomFromText( 'POINT(40 -100)' ));
INSERT INTO geometry (coord) VALUES( GeomFromText( 'POINT(1 1)' ));

Get those X,Y coordinates back from the table:

SELECT X(coord), Y(coord) FROM geometry

Get points within a bounding rectangle:

SELECT MBRContains(
	GeomFromText( 'POLYGON((0 0,0 3,3 3,3 0,0 0))' ),
	coord
)
FROM geometry

MySQL has some powerful, and perhaps underused spatial extensions, but the most interesting functions are still unimplemented: “Note: Currently, MySQL does not implement these functions…”

Among those as-yet unimplemented functions is DISTANCE(). Alternatives can be found here and here, though neither is clean or simple. I wonder if a simple MBRContains() is good enough, though…

Found in the MySQL 5.0 Reference Manual:

• Related(g1,g2,pattern_matrix)
  Returns 1 or 0 to indicate whether the spatial relationship specified by pattern_matrix exists between g1 and g2. Returns –1 if the arguments are NULL. The pattern matrix is a string. Its specification will be noted here if this function is implemented.

(emphasis mine.)