On Apr 16, 2009, at 10:21 PM, Milton Wong wrote:
>
> Hi I am quite a newbie in Ruby. I want to sort a list of locations by
> relative distance (shortest to farthest relative to my location) on
> the
> fly. For example, let say I am at x and y coordinate, I have other
> points in the map around me. I want to be able to list the other
> points
> in terms of the shortest distance from me to the farthest. I store
> longitude and latitude information on the database. However, I cannot
> store the relative distance permanently, as (i) number of points
> change
> in real time; and (ii) I don't have relationship with the other
> points,
> which means the many-to-many tables are still empty.
>
> Any ideas?
Google for "earth distance sql"... or trust that the below is right :)
This assumes that some_table has columns for latitude and longitude
and that you've set variables for latitude, longitude and radius (in
miles) to search on.
SELECT * FROM some_table WHERE
(3960 * 2 * ASIN( SQRT( (1 - COS(RADIANS(latitude - #{latitude})))
/ 2 + COS(RADIANS(#{latitude}))
* COS(RADIANS(latitude))
* (1 - COS(RADIANS(longitude - #{longitude}))) / 2))) <= #{radius}
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