Mapstraction.prototype.getXmlHttp = function() {
  var req = false;
  if(window.XMLHttpRequest) {
    try {
      req = new XMLHttpRequest();
    } catch(e) {
      req = false;
    }
  } else if(window.ActiveXObject) {
    try {
      req = new ActiveXObject("Msxml2.XMLHTTP");
    } catch(e) {
      try {
        req = new ActiveXObject("Microsoft.XMLHTTP");
      } catch(e) {
        req = false;
      }
    }
  }
  return req;
}

Mapstraction.prototype.openGPX = function(url) {
  var request = this.getXmlHttp();
  var mapstractionplot = this.plotGPX;
  request.onreadystatechange = function() { 
    if (request.readyState == 4) {
      var xmlDoc = request.responseXML; // relies on correct mimetype
      mapstractionplot(xmlDoc);
    }
  }
  request.setRequestHeader('Content-Type','text/xml');
  request.open("GET", url, true);
  request.send("");
}

Mapstraction.prototype.addPolyLine = function(points) {
  switch(this.api) {
    case 'google':
      var gpoints = [];
      for (var i = 0; i < points.length; i++) {
        gpoints[i] = new GLatLng(points[i].lat,points[i].lon);
      }
      map.addOverlay(new GPolyline(gpoints));
      break;
    default:
      alert('polyline not supported by Mapstraction for ' + api);
  }
}

Mapstraction.prototype.plotGPX = function(xmlDoc) {

  // parse tracks from GPX file...
  var trks = xmlDoc.documentElement.getElementsByTagName("trk");
  var lastPoint;
  for (var i = 0; i < trks.length; i++) {
    var trksegs = trks[i].getElementsByTagName("trkseg");
    for (var j = 0; j < trksegs.length; j++) {
      var trkpts = trksegs[j].getElementsByTagName("trkpt");
      
      if (trkpts.length > 1) {
      
        var points;
	
        for (var diff = 0.000000001, count = 201; count > 200; diff *= 5) {
          points = [];
	
          var first = true;
          var oldlon = 0.0;
          var oldlat = 0.0;
          var oldvx = 0.0;
          var oldvy = 0.0;
	
          var lat = parseFloat(trkpts[0].getAttribute("lat"));
          var lon = parseFloat(trkpts[0].getAttribute("lon"));
	  points[points.length] = new LatLonPoint(lat,lon);
          count = 1;

          for (var k = 1; k < trkpts.length; k++) {
            lat = parseFloat(trkpts[k].getAttribute("lat"));
            lon = parseFloat(trkpts[k].getAttribute("lon"));
	    
	    vx = oldlon - lon;
	    vy = oldlat - lat;
	    
	    if ( ((oldvx - vx)*(oldvx - vx))+((oldvy - vy)*(oldvy - vy)) > diff ) {
	      count += 1;
	      points[points.length] = new LatLonPoint( lat, lon );
	      oldvx = vx;
	      oldvy = vy;
	      oldlat = lat;
	      oldlon = lon;
	    }
	  }
	} // for trkpts
	this.addOverlay(points);
	lastPoint = points[0];
      } // if
    } // for trksegs
  } // for trks

  // parse waypoints from GPX file
  var wpts = xmlDoc.documentElement.getElementsByTagName("wpt");
  for (var i = 0; i < wpts.length; i++) {
    var text = "Waypoint info:<br/>"
    for (var child = wpts[i].firstChild; child; child = child.nextSibling) {
      if (child.text) {
        text += child.nodeName + ": " + child.text + "<br/>";
      }
      else if (child.nodeType != 3) {
        text += child.nodeName + ": " + child.firstChild.nodeValue + "<br/>";
      }
    }
    var point = new LatLonPoint(parseFloat(wpts[i].getAttribute("lat")), parseFloat(wpts[i].getAttribute("lon")));
    var marker = new Marker(point);
    marker.setInfoBubble(text);
    this.addMarker(marker);
    lastPoint = point;
  }
}