var ruler1;
var ruler2;
var rulerpoly;
var ruler1label;
var ruler2label;

function addruler() {
		
	var image = 'http://maps.gstatic.com/intl/it_it/mapfiles/marker_greenA.png';
	 ruler1 = new google.maps.Marker({
		position: map.getCenter() ,
		map: map,
		icon: image,
		draggable: true
	});
     var image = 'http://maps.gstatic.com/intl/it_it/mapfiles/marker_greenB.png';
	 ruler2 = new google.maps.Marker({
		position: map.getCenter() ,
		map: map,
		icon: image,
		draggable: true
	});
	ruler1label = new Label({map: map });
	ruler2label = new Label({ map: map });
	ruler1label.bindTo('position', ruler1, 'position');
	ruler2label.bindTo('position', ruler2, 'position');

	 	rulerpoly = new google.maps.Polyline({
		path: [ruler1.position, ruler2.position] ,
		strokeColor: "yellow",
		strokeOpacity: .5,
		strokeWeight: 3
		
	});
	
	rulerpoly.setMap(map);
	
	ruler1label.set('text',distance( ruler1.getPosition().lat(), ruler1.getPosition().lng(), ruler2.getPosition().lat(), ruler2.getPosition().lng()));
	ruler2label.set('text',distance( ruler1.getPosition().lat(), ruler1.getPosition().lng(), ruler2.getPosition().lat(), ruler2.getPosition().lng()));
	google.maps.event.addListener(ruler1, 'drag', function() {
		rulerpoly.setPath([ruler1.getPosition(), ruler2.getPosition()]);
	ruler1label.set('text',distance( ruler1.getPosition().lat(), ruler1.getPosition().lng(), ruler2.getPosition().lat(), ruler2.getPosition().lng()));
		ruler2label.set('text',distance( ruler1.getPosition().lat(), ruler1.getPosition().lng(), ruler2.getPosition().lat(), ruler2.getPosition().lng()));
	});

	google.maps.event.addListener(ruler2, 'drag', function() {
		rulerpoly.setPath([ruler1.getPosition(), ruler2.getPosition()]);
		ruler1label.set('text',distance( ruler1.getPosition().lat(), ruler1.getPosition().lng(), ruler2.getPosition().lat(), ruler2.getPosition().lng()));
		ruler2label.set('text',distance( ruler1.getPosition().lat(), ruler1.getPosition().lng(), ruler2.getPosition().lat(), ruler2.getPosition().lng()));
	});

}


function distance(lat1,lon1,lat2,lon2) {
	var R = 6371; // km (change this constant to get miles)
	var	dLat = (lat2-lat1) * Math.PI / 180;
	var	dLon = (lon2-lon1) * Math.PI / 180; 
	var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
		Math.cos(lat1 * Math.PI / 180 ) * Math.cos(lat2 * Math.PI / 180 ) * 
		Math.sin(dLon/2) * Math.sin(dLon/2); 
	var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
	var d = R * c;
	if (d>1) return "AB = " + Math.round(d*1000)/1000+" km";
	else if (d<=1) return "AB = " + Math.round(d*1000)+" m";
	return d;
}