Search a location, drag the marker to adjust the position and get the GPS coordinates.

Code snippet to create a Google map and deect user location,
this project uses Google Maps Javascript API v3

<script src="https://maps.googleapis.com/maps/api/js?v=3.exp"></script>

<script>
    var map;
    function geoinitialize() {
        var mapOptions = {
            zoom: 6
        };
        map = new google.maps.Map(
            document.getElementById('map-canvas'), 
            mapOptions
        );
        
        // Try HTML5 geolocation
        if(navigator.geolocation) {
            navigator.geolocation.getCurrentPosition(function(position) {
                var pos = new google.maps.LatLng(
                    position.coords.latitude, 
                    position.coords.longitude
                );
                map.setCenter(pos);
                
                var marker = new google.maps.Marker({
                    map:map,
                    draggable:true,
                    animation: google.maps.Animation.DROP,
                    position: pos
                });
            });
        }
    }
    google.maps.event.addDomListener(window, 'load', geoinitialize);
</script>

<div id="map-canvas"></div>