Generating KML / XML on the fly in Ruby on Rails June 7th, 2007

KML can now be used both in Google Maps and Google Earth.
I wrote a simple KML generator using Builder and Rails.
I also used an RSS parser to read geographic coords from an RSS feed which is in use now at Baleen.org, but that is a code story for another day..

I wanted to post some code snips from the project, cause it's cool.

The view "kml.rxml" 

xml = Builder::XmlMarkup.new(:indent => 2)

xml.instruct! :xml

xml.kml( "kmlns" => "http://earth.google.com/kml/2.1" ) do
  xml.Document {
    xml.name("someplaces")
    xml.description("someplaces.org locator")
    xml.Style( "id" => "highlight" ) {
      xml.IconStyle {
        xml.Icon {
          xml.href("http://URL to transparent 32x32 png image.png")
        }
      }
    }
    Place.find_all.each do |p|
    xml.Place {
      xml.name(p.tooltip)
      xml.description {
        x=p.popup.dup
        xml.cdata!("#{x.slice!(1..250)}<br><a href=#{p.ext_url}>..Read more</a>")
        }
      xml.styleUrl("#highlight")
      xml.Point {
        xml.coordinates("#{p.x},#{p.y},4")
      }
    }
    end
  }
end
In the controller, you must specify the following headers. 
def kml
  render_without_layout
  @headers["Content-Type"] = "application/vnd.google-earth.kml+xml kml; charset=utf-8"
  @headers["Content-Disposition"] = "attachment; filename=someplaces.kml"
end
Here is the migration I used: "001_create_places.rb" For storing latitude/longitude and a few other useful Google Earth / Maps data to be used in the KML 
class CreatePlaces < ActiveRecord::Migration
  def self.up
    create_table :places do |t|
      t.column :x, :string
      t.column :y, :string
      t.column :ext_url, :string
      t.column :tooltip, :string
      t.column :popup, :text
    end
  end

  def self.down
    drop_table :places
  end
end
Use a route to behave as a downloadable file. 
map.connect '/someplaces.kml', :controller => 'places', :action => 'kml'
That's all you need to start generating KML on the fly with Rails. Have fun!

Bonus Code !! Example Javascript for Google Maps API that loads up KML from an URL.

var geoXml = new GGeoXml("http://URL to someplaces.kml");
    function load() {
      if (GBrowserIsCompatible()) {
        var map = new GMap2(document.getElementById("map"));
	map.setCenter(new GLatLng(37.12755479789267,-112.7487179140864),3);
	map.setMapType(new GMapType([G_SATELLITE_MAP.getTileLayers()[0]], G_NORMAL_MAP.getProjection(), "test", {}));
	map.addOverlay(geoXml);
        map.addControl(new GSmallMapControl());
        map.addControl(new GMapTypeControl());
      }
    }
Also, make sure you have 2.x as the version string where you delcare the Javascript, otherwise your placemarks might go missing! 
<script src="http://maps.google.com/maps?file=api&amp;v=2.x&amp;key=YOURKEY>

Leave a comment if this tutorial helped you. Thanks!

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