Google Maps tool for accurately positioning image overlay?

Question

I am hoping someone can point me in the right direction.

I have a Google Map that loads markers from an XML file, along with various other map elements, works great. However I now need to overlay a PNG image onto the map.

I have tried for hours to correctly align the PNG over the top of the site but just cannot find the exact two co-ordinates I need (south-west and north-east). Is there a tool for doing this? Ideally upload the image and drag the corners to fit, and it outputs the two co-ordinates (lat/lng) you need?

I have tried using this tool: http://overlay-tiler.googlecode.com/svn/trunk/upload.html - but it has three contact points.

I have also tried using this tool: http://www.birdtheme.org/useful/customoverlay.html - but you cannot resize the image once uploaded to the map and you get one chance at clicking the south-west marker!

I can also use Google Earth to align the PNG perfectly, but I can't see a way of outputting the lat/lng points.

Any advice would be much appreciated.

Answer 1

Heres a working example of André Dion's explanation.

http://jsfiddle.net/4cWCW/3/

var overlay;

DebugOverlay.prototype = new google.maps.OverlayView();

function initialize() {
  var mapOptions = {
    zoom: 15,
    center: new google.maps.LatLng(40.743388,-74.007592)
  };

  var map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);
  var swBound = new google.maps.LatLng(40.73660837340877, -74.01852328);
  var neBound = new google.maps.LatLng(40.75214181, -73.99661518216243);
  var bounds = new google.maps.LatLngBounds(swBound, neBound);

   console.log(map);
  var srcImage = 'http://robincwillis.com/top/splash/04.jpg';

  overlay = new DebugOverlay(bounds, srcImage, map);

  var markerA = new google.maps.Marker({
            position: swBound,
            map: map,
            draggable:true
        });

    var markerB = new google.maps.Marker({
        position: neBound,
        map: map,
        draggable:true
    });

    google.maps.event.addListener(markerA,'drag',function(){

        var newPointA = markerA.getPosition();
        var newPointB = markerB.getPosition();
        var newBounds =  new google.maps.LatLngBounds(newPointA, newPointB);
        overlay.updateBounds(newBounds);
    });

  google.maps.event.addListener(markerB,'drag',function(){

      var newPointA = markerA.getPosition();
      var newPointB = markerB.getPosition();
      var newBounds =  new google.maps.LatLngBounds(newPointA, newPointB);
      overlay.updateBounds(newBounds);
  });

    google.maps.event.addListener(markerA, 'dragend', function () {

        var newPointA = markerA.getPosition();
        var newPointB = markerB.getPosition();
        console.log("point1"+ newPointA);
        console.log("point2"+ newPointB);
    });

    google.maps.event.addListener(markerB, 'dragend', function () {
        var newPointA = markerA.getPosition();
        var newPointB = markerB.getPosition();
        console.log("point1"+ newPointA);
        console.log("point2"+ newPointB);
    });

}

function DebugOverlay(bounds, image, map) {

  this.bounds_ = bounds;
  this.image_ = image;
  this.map_ = map;
  this.div_ = null;
  this.setMap(map);
}

DebugOverlay.prototype.onAdd = function() {

  var div = document.createElement('div');
  div.style.borderStyle = 'none';
  div.style.borderWidth = '0px';
  div.style.position = 'absolute';
  var img = document.createElement('img');
  img.src = this.image_;
  img.style.width = '100%';
  img.style.height = '100%';
  img.style.opacity = '0.5';
  img.style.position = 'absolute';
  div.appendChild(img);
  this.div_ = div;
  var panes = this.getPanes();
  panes.overlayLayer.appendChild(div);
};

DebugOverlay.prototype.draw = function() {
  var overlayProjection = this.getProjection();
  var sw = overlayProjection.fromLatLngToDivPixel(this.bounds_.getSouthWest());
  var ne = overlayProjection.fromLatLngToDivPixel(this.bounds_.getNorthEast());
  var div = this.div_;
  div.style.left = sw.x + 'px';
  div.style.top = ne.y + 'px';
  div.style.width = (ne.x - sw.x) + 'px';
  div.style.height = (sw.y - ne.y) + 'px';
};


DebugOverlay.prototype.updateBounds = function(bounds){
    this.bounds_ = bounds;
    this.draw();
};

DebugOverlay.prototype.onRemove = function() {
  this.div_.parentNode.removeChild(this.div_);
  this.div_ = null;
};

initialize();