From: Mark Ericson <mark.ericson@...>
Date: 2005-12-14T03:09:32+09:00
Subject: Re: US Zipcode API for Ruby?

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Excellent!  The only thing remaining is an efficient algorithm for a search
for all zipcodes within a given radius.

I suppose one technique might be to first narrow the databse search within =
a
given a given square latitude/longitude range and then filter those results
by testing that they are within the given circle radius

On 12/13/05, Dan Diebolt <dandiebolt@yahoo.com> wrote:
>
> There is a 40,000+ zip code database in CivicSpace labs that has lat and
> long by zip code:
>
>   http://civicspacelabs.org/home/developers/download
>
>   http://civicspacelabs.org/releases/zipcodes/zipcodes-csv-10-Aug-2004.zi=
p
>
>   Distance between two points (lat, long) is calculated using the
> Haversine formula:
>
>     dlon =3D lon2 - lon1
>   dlat =3D lat2 - lat1
>   a =3D (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
>   c =3D 2 * atan2(sqrt(a), sqrt(1-a))
>   d =3D R * c
>
>   See the following link or google for more:
>
>   http://mathforum.org/library/drmath/view/51879.html
>
>
> ---------------------------------
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>

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