Introduction
This article describe how to convert the mouse position x/y to the map lat/lng in Google Maps.
The Program
Simply get the bounds of map and calculate the lat/lng based on the mouse x/y and the width/henght of map div.
The result has a little bit bias, but accurate enough.
<!DOCTYPE html>
<!-- tested with google chrome -->
<html>
<head>
<script src="https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=false"></script>
<script>
var map,
mLat,
mLng;
function initialize() {
var mapOptions = {
zoom: 12,
center: new google.maps.LatLng(33.397, -81.644),
mapTypeId: google.maps.MapTypeId.ROADMAP
};
map = new google.maps.Map(document.getElementById('map_canvas'),
mapOptions
);
// add a click event listener to
// get the lat/lng from click event of map
google.maps.event.addListener(map, 'click', function(event) {
mLat = event.latLng.lat();
mLng = event.latLng.lng();
document.getElementById('latMap').value = mLat;
document.getElementById('lngMap').value = mLng;
});
}
function mapDivClicked (event) {
var target = document.getElementById('map_canvas'),
posx = event.pageX - target.offsetLeft,
posy = event.pageY - target.offsetTop,
bounds = map.getBounds(),
neLatlng = bounds.getNorthEast(),
swLatlng = bounds.getSouthWest(),
startLat = neLatlng.lat(),
endLng = neLatlng.lng(),
endLat = swLatlng.lat(),
startLng = swLatlng.lng(),
lat = startLat + ((posy/350) * (endLat - startLat)),
lng = startLng + ((posx/500) * (endLng - startLng));
document.getElementById('posX').value = posx;
document.getElementById('posY').value = posy;
document.getElementById('lat').value = lat; // calculated lat
document.getElementById('lng').value = lng; // calculated lng
// the error rate
document.getElementById('latErr').value = ((mLat - lat) / (endLat - startLat) * 100).toFixed(2);
document.getElementById('lngErr').value = ((mLng - lng) / (endLng - startLng) * 100).toFixed(2);
}
google.maps.event.addDomListener(window, 'load', initialize);
</script>
</head>
<body>
<div id="map_canvas" onclick="mapDivClicked(event);" style="height: 350px; width: 500px;"></div>
<div>
mouse x: <input id="posX" />
mouse y: <input id="posY" />
</div>
<div>
lat: <input id="lat" />
lng: <input id="lng" />
</div>
<div>
lat from map: <input id="latMap" />
lng from map: <input id="lngMap" />
</div>
<div>
lat error rate: <input id="latErr" /> %
lng error rate: <input id="lngErr" /> %
</div>
</body>
</html>
The Result
Reference
https://developers.google.com/maps/documentation/javascript/reference
Download
File at github
https://github.com/benbai123/HTML_CSS_Javascript_practice/blob/master/WebService_WebAPIs/Google/GoogleMap/mouse_position_to_latlng.html
No comments:
Post a Comment