I’m still very new to Ruby, however am growing to like the language more
and more as I use it.
Presently, I’m looking for some classes(I’m used to java, sorry, not
sure what you’d call them in Ruby) that can measure geographic distances
based on information like zip, city, state, etc.
An example of the sort of the functionality I’m looking for would be the
“find locations withing X miles of zip code 01234” searches you can do
with google maps or mapquest.
Below are my zipcode notes. None of this originates from me, so I
really can’t help much if you should have questions. Caveat emptor.
But there’s probably a gem or two hidden somewhere in all the cruft.
You can get zip code data and a MySQL schema here:
There is some PHP code there for searching that can easily be ported to
Ruby:
class ZipCode < ActiveRecord::Base
def search(radius = 30)
ZipCode.find_by_sql("SELECT * FROM zip_codes WHERE
(POW((69.1*(lon-#{self.lon})cos(#{self.lat}/57.3)),2)+
POW((69.1(lat-#{self.lat})),2))<(#{radius}*#{radius})")
end
end
OR
This can be done through the use of free Geocoding websites and a little
math.
One such site is GeoCoder.us (Web based, or API for a fee …I beleive),
where you can input the addresses (not just zip codes… which is what
you asked for, but its close. “1 main street,
ZIP CODE” is usually a fair assumption.
Once you have both longitude/latitude coordinates for the addresses, you
can then calculate the distance between the two. Here are two links
which explain how:
As for Rails/Ruby solutions… I don’t know of any off hand, but there is
a Perl interface to Geocoder.us which may be easily ported or referenced
to help you on your way:
SCAN_RE =
/“(\d{5})”,“([^”]+)“,”(…)“,”([\d.-]+)“,”([\d.-]+)“,”([\d-]+)“,”(\d)"/
SQL = “INSERT INTO zips(zip, city, state, lat, long, timezone, dst)
VALUES (?, ?, ?, ?, ?, ?, ?)”
TABLE_SCHEMA = "CREATE TABLE zips (
id INTEGER NOT NULL PRIMARY KEY,
zip VARCHAR(5) NOT NULL,
city TEXT NOT NULL,
state VARCHAR(2) NOT NULL,
lat FLOAT NOT NULL,
long FLOAT NOT NULL,
timezone INTEGER NOT NULL,
dst BOOLEAN NOT NULL
sql = “SELECT lat, long FROM zips WHERE zip = ?”
src_lat, src_long = db.get_first_row(sql, src_zip).map { |v| v.to_f }
unless src_lat && src_long
$stderr.puts “Unknown zip code ‘#{src_zip}’”
exit -1
end
calculate min/max lat/long
ret, range = [], radius / 69.0
get all codes within given rectangle
sql = “SELECT lat, long, city, state, zip
FROM zips
WHERE lat > ? AND lat < ?
AND long > ? AND long < ?”
args = [src_lat - range, src_lat + range,
src_long - range, src_long + range]
db.prepare(sql).execute(*args).each do |row|
# get row values, convert lat/long to floats
dst_lat, dst_long, dst_zip, dst_city, dist_st = row
dst_lat, dst_long = dst_lat.to_f, dst_long.to_f
# calculate distance between zip codes. if dst_zip is within the
# specified radius, then add it to the list of results
d = Math.sqrt((dst_lat - src_lat) ** 2 + (dst_long - src_long) **
ret << [dst_zip, dst_city, dist_st, d * 69.0] if d <= range
end
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
That’s all the code above does. There’s some room for optimization
there; for example, you could create a region field, then calculate list
of regions that intersect with the search radius. If you index on the
region field, then the query becomes essentially an index lookup instead
of a lat/long comparison (you still have to do the second distance
calculation, of course).
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