Geolocation SQL query not finding exact location
- by Iridium52
I have been testing my geolocation query for some time now and I haven't found any issues with it until now.
I am trying to search for all cities within a given radius, often times I'm searching for cities surrounding a city using that city's coords, but recently I tried searching around a city and found that the city itself was not returned.
I have these cities as an excerpt in my database:
city latitude longitude
Saint-Mathieu 45.316708 -73.516253
Saint-Édouard 45.233374 -73.516254
Saint-Michel 45.233374 -73.566256
Saint-Rémi 45.266708 -73.616257
But when I run my query around the city of Saint-Rémi, with the following query...
SELECT tblcity.city, tblcity.latitude, tblcity.longitude,
truncate((degrees(acos( sin(radians(tblcity.latitude))
* sin(radians(45.266708))
+ cos(radians(tblcity.latitude))
* cos(radians(45.266708))
* cos(radians(tblcity.longitude - -73.616257) ) ) )
* 69.09*1.6),1) as distance
FROM tblcity HAVING distance < 10 ORDER BY distance desc
I get these results:
city latitude longitude distance
Saint-Mathieu 45.316708 -73.516253 9.5
Saint-Édouard 45.233374 -73.516254 8.6
Saint-Michel 45.233374 -73.566256 5.3
The town of Saint-Rémi is missing from the search.
So I tried a modified query hoping to get a better result:
SELECT tblcity.city, tblcity.latitude, tblcity.longitude,
truncate(( 6371 * acos( cos( radians( 45.266708 ) )
* cos( radians( tblcity.latitude ) )
* cos( radians( tblcity.longitude )
- radians( -73.616257 ) )
+ sin( radians( 45.266708 ) )
* sin( radians( tblcity.latitude ) ) ) ),1) AS distance
FROM tblcity HAVING distance < 10 ORDER BY distance desc
But I get the same result...
However, if I modify Saint-Rémi's coords slighly by changing the last digit of the lat or long by 1, both queries will return Saint-Rémi. Also, if I center the query on any of the other cities above, the searched city is returned in the results.
Can anyone shed some light on what may be causing my queries above to not display the searched city of Saint-Rémi? I have added a sample of the table (with extra fields removed) below.
I'm using MySQL 5.0.45, thanks in advance.
CREATE TABLE `tblcity` (
`IDCity` int(1) NOT NULL auto_increment,
`City` varchar(155) NOT NULL default '',
`Latitude` decimal(9,6) NOT NULL default '0.000000',
`Longitude` decimal(9,6) NOT NULL default '0.000000',
PRIMARY KEY (`IDCity`)
) ENGINE=MyISAM AUTO_INCREMENT=52743 DEFAULT CHARSET=latin1 AUTO_INCREMENT=52743;
INSERT INTO `tblcity` (`city`, `latitude`, `longitude`) VALUES
('Saint-Mathieu', 45.316708, -73.516253),
('Saint-Édouard', 45.233374, -73.516254),
('Saint-Michel', 45.233374, -73.566256),
('Saint-Rémi', 45.266708, -73.616257);
