Spatial Extensions in MySQL 5.0.16 (the version I'm on) seem really
slow. I must be missing something, but can't figure out what. Some
background:

I'm trying to speed up a query that fetches the nearest 10 records
(essentially, latitude/longitude pairs, stored in a Geometry point
column) to a given point (latitude/longitude). Here's the query I'm
using right now, which works but is slow:

SELECT latitude, longitude,
GLength(LineStringFromWKB(LineString(AsBinary(coor dinates),
AsBinary(GeomFromText('POINT(51 -114)'))))) AS distance FROM places
ORDER BY distance ASC LIMIT 10

latitude longitude distance
51.00137160 -114.00182421 0.0022823296615694
50.99412759 -114.00182513 0.0061494958106356
51.00859980 -114.00181734 0.0087897260887692
....

It takes about 2.3 seconds to execute on a MacBook Pro. Now, the table
is big--over 800,000 rows. And the above query is a one-second
improvement over this original one:

SELECT latitude, longitude, SQRT( POW( 69.1 * ( latitude - 51) , 2 ) +
POW( 69.1 * (-114 - longitude) * COS( latitude / 57.3 ) , 2 ) ) AS
distance FROM places ORDER BY distance ASC LIMIT 0,10

But I expected much better. I created a spatial index on the
coordinates column, but it is not being used (I did EXPLAIN). This is
not surprising, since there's a calculation that needs to be performed
on every single row. But is there a faster way to fetch the closest
records to a given point? The MySQL docs are incredibly terse and I
can't find any other examples or code to copy.

Any help is much appreciated.

....R

PS: For clarity, here is the table structure:

CREATE TABLE `places` (
`id` mediumint(8) unsigned NOT NULL auto_increment,
`latitude` decimal(10,8) NOT NULL,
`longitude` decimal(12,8) NOT NULL,
`coordinates` point NOT NULL,
PRIMARY KEY (`id`),
SPATIAL KEY `latlng` (`coordinates`(32))
) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci
AUTO_INCREMENT=845891 ;