MySQL Forums
Forum List  »  GIS

Re: Zip Code Proximity search - Examples II
Posted by: p dontthink
Date: June 06, 2006 04:09AM

> it seems that I will need to convert these lat/long coordinates so that
> I can do a radius search using miles as the distance units?

yep. you have to do a little of your own legwork.

http://www.google.com/

note that lat/long are given in degrees (decimal degrees or degrees/minutes/seconds)

problem is that while a degree of latitude remains mostly constant everywhere on earth (69.172 miles, do your own math from there), longitudinal distances are quite different depending on where you are, what latitude you are talking about. it goes from I think 69.172 at the equator to 0 at the poles, so usually you have to use a formula for this figure along the lines of:

cos(latitude) * 69.172

this is all very rough anyway, so, say if you expect all your lookups to be in a given country, you could calculate that number with the latitude of the middle of that country and call it a day.

this way, you have your "sloppy" rectangle for parsing your initial dataset, and then you can refine the search if needed (and sort it) in your application with more accurate distance formulas.

BTW, no one on this thread has mentioned that a commonly used formula for distance computations that is reasonably quick and is much more accurate than the great circle/Haversine formulas being shown in this thread is the Vincenty formula. Google it and you're good to go.

oh, also in case you need it, some random conversion factors:

convert degrees/minutes/seconds to decimal degrees:
decimal degrees = degrees + (minutes + seconds / 60) / 60

convert from decimal degrees to radians:
radians = degrees * (pi / 180)
or:
radians = degrees / 57.29577951

3437.7467707849392526 appears to be the factor to convert from nautical miles to radians

and apparently:
statute (land) miles = nautical miles * 1.150779

Options: ReplyQuote


Subject
Views
Written By
Posted
27649
October 19, 2004 06:04AM
10714
October 19, 2004 07:55AM
9108
October 19, 2004 11:14AM
10153
October 21, 2004 09:28AM
9064
October 19, 2004 06:59PM
7523
October 20, 2004 07:39AM
7528
October 21, 2004 09:10AM
8654
October 22, 2004 07:17AM
6623
October 23, 2004 02:48AM
6131
October 23, 2004 03:09AM
6181
October 23, 2004 03:12AM
6080
October 23, 2004 02:59PM
7754
October 24, 2004 12:34PM
5373
October 24, 2004 01:31PM
12896
October 21, 2005 10:21AM
5467
D C
January 28, 2006 05:24AM
5013
March 02, 2006 04:24PM
7099
October 09, 2007 09:28AM
5643
December 06, 2005 05:34AM
6857
December 06, 2005 06:36AM
5202
December 24, 2005 01:10PM
8602
December 26, 2005 03:49PM
5322
October 09, 2007 09:36AM
Re: Zip Code Proximity search - Examples II
8411
June 06, 2006 04:09AM
29055
December 13, 2007 04:10PM
6074
April 05, 2006 02:59PM
4587
May 02, 2006 03:22PM
5488
May 05, 2006 09:44AM
14177
June 25, 2006 09:32PM
5355
August 30, 2006 12:54PM
5838
July 14, 2007 01:09AM
7529
November 03, 2006 10:25AM


Sorry, you can't reply to this topic. It has been closed.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.