routes_to.rb

 def routes_to
    lat = params[:lat].to_f
    lon = params[:lon].to_f
    features = []
    TrackPoint.collection.aggregate([{'$geoNear' => {near: [lon, lat], spherical: true, num: 500, maxDistance: 5/6371, distanceMultiplier: 6371, distanceField: 'dist.calculated'}}, {'$group' => {'_id' => '$route_id'}}]).each { |route_id|
      route = Route.find(route_id[:_id])
      gjson_line = {
          :type => "Feature",
          :geometry => {
              :type => "LineString",
              :coordinates => route.track_points.map { |p| p.location }
          }
      }
      features << gjson_line
    }

    feature_collection = {
        :type => "FeatureCollection",
        :features => features
    }
    render :json => Yajl::Encoder.encode(feature_collection), :content_type => 'application/json'
  end