first_route.rb

 def route_to
    lat = params[:lat].to_f
    lon = params[:lon].to_f
    first_point = TrackPoint.where({:location => {'$nearSphere' => [lat, lon]}}).limit(1).first()
    route = Route.find(first_point.route_id)
    gjson_line = {
        :type => "Feature",
        :geometry => {
            :type => "LineString",
            :coordinates => route.track_points.map { |p| p.location }
        }
    }
    feature_collection = {
        :type => "FeatureCollection",
        :features => [gjson_line]
    }
    render :json => Yajl::Encoder.encode(feature_collection), :content_type => 'application/json'
  end