function compute() {
            var startPoint = start.features[0]; 
            var stopPoint = stop.features[0]; 

            if (startPoint && stopPoint) { 
                var result = { 
                    startpoint: startPoint.geometry.x + ' ' + startPoint.geometry.y, 
                    finalpoint: stopPoint.geometry.x + ' ' + stopPoint.geometry.y, 
                    //method: OpenLayers.Util.getElement('method').value,
                    method: getradiovalue(),
                    region: "streets",
                    srid: "-1"
                }; 
                OpenLayers.loadURL("routing.php",
                                   OpenLayers.Util.getParameterString(result), 
                                   null, 
                                   displayRoute);
            } 
        }
        
        function randomString() {
	var chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz";
	var string_length = 20;
	var randomstring = '';
	for (var i=0; i<string_length; i++) {
		var rnum = Math.floor(Math.random() * chars.length);
		randomstring += chars.substring(rnum,rnum+1);
	}
	return randomstring;
      }

       function openXMLrequest() {
                  var request = false;
                   try {
                     request = new XMLHttpRequest();
                   } catch (trymicrosoft) {
                     try {
                       request = new ActiveXObject("Msxml2.XMLHTTP");
                     } catch (othermicrosoft) {
                       try {
                         request = new ActiveXObject("Microsoft.XMLHTTP");
                       } catch (failed) {
                         request = false;
                       }  
                     }
                   }

           if (!request)
             alert("Error initializing XMLHttpRequest!");
                var tid = randomString();
                 var url = "http://localhost/~yancho/xml_parser.php?tid=" + escape(tid);
                 request.open("GET", url, true);
                 request.send(null);
         }

       function displayRoute(response) {
            if (response && response.responseXML) {
                // erase the previous results
                result.removeFeatures(result.features);
                
                var xml_get = openXMLrequest();

                var edges = response.responseXML.getElementsByTagName('edge');
                var features = [];
                for (var i = 0; i < edges.length; i++) {
                    var wkt = edges[i].getElementsByTagName('wkt')[0].textContent;
                    var g = parser.read(wkt);
                    features.push(g);
                }
                result.addFeatures(features);
            }
        }