Geocoding, REXML and the Missing Method

fred@fredjean.net (Frederic Jean) — Mon, 20 Feb 2006 02:35:48 +0000

Scott Davis introduces the audience of his Real World Mapping presentation to the geocoder.us web site, which allows anyone to transform US based addresses to longitude and latitude coordinates. There are many options beyond the web based UI, including SOAP, XML-RPC, and RESTful web services. We will be using the RESTful RDF service for this demonstration.

The first step is to find (and URL encode) an address. For this demonstration, we will be using "Mission & Valencia Sts, San Francisco CA" as the address. You will see the following XML document if you point a browser at http://rpc.geocoder.us/service/rest?address=Mission+%26+Valencia+Sts%2C+San+Francisco+CA:

<rdf:RDF>
  <geo:Point rdf:nodeID="aid06646235">
    <dc:description>Mission St and Valencia St, San Francisco CA 94110</dc:description>
    <geo:long>-122.420082</geo:long>
    <geo:lat>37.74533</geo:lat>
  </geo:Point>
</rdf:RDF>

This is technically an RDF document. It can still be parsed as a regular XML document though. Let's define a Location class:

require 'rexml/document'
require 'net/http'

class Location
  require REXML

  def initialize(address)
    geocoder = Net::HTTP.new("rpc.geocode.us", 80)
    query = "/service/rest?address=#{address}"
    query.gsub!(/ /, "+")
    @entry = Document.new geocoder.get(query).body
  end
  
  def long
    @entry.elements["//geo:long"].text
  end
  
  def lat
    @entry.elements["//geo:lat"].text
  end
  
  def desc
    @entry.elements["//dc:description"].text
  end
end

From there, you can create a Location object and get the coordinates:

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location = Location.new "Mission St and Valencia St, San Francisco CA 94110"
location.lat
location.long

From there, you can use the location in a mapping application (such as a Google Maps mashup for example...)

Out of my mind...: Geocoding, REXML and the Missing Method

Geocoding, REXML and the Missing Method