google map 得到用户 地理位置信息
解析：
首先通过w3c Geolocation 标准得到位置信息，此标准是html5的一部分。如果浏览器不支持w3c Geolocation标准，再通过google gears软件得到位置信息，gears是一款支持离线工作的软件。
Google Gears有几个主要的API组件：
一个本地服务器，用来存储和读取离线程序资源（包括HTML, JavaScript, images等）。
一个小型数据库（以SQLite构建），用来储存本地数据。
一个工作池，用来让开发者将本地数据与服务器端后台同步。
一个桌面模型可使网络程序的操作贴近桌面程序。
一个地理定位模型，能够让网络程序侦测到目前用户的地理位置。
源码：
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
<meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
<title>Google Maps JavaScript API v3 Example: Map Geolocation</title>
<link href="http://code.google.com/apis/maps/documentation/javascript/examples/default.css" rel="stylesheet" type="text/css" />
<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=true"></script>
<script type="text/javascript" src="http://code.google.com/apis/gears/gears_init.js"></script>
<script type="text/javascript">
var initialLocation;
var siberia = new google.maps.LatLng(60, 105);
var newyork = new google.maps.LatLng(40.69847032728747, -73.9514422416687);
var browserSupportFlag = new Boolean();
var map;
var infowindow = new google.maps.InfoWindow();
function initialize() {
var myOptions = {
zoom: 6,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
// Try W3C Geolocation method (Preferred)
if(navigator.geolocation) {
browserSupportFlag = true;
navigator.geolocation.getCurrentPosition(function(position) {
initialLocation = new google.maps.LatLng(position.coords.latitude,position.coords.longitude);
contentString = "Location found using W3C standard";
map.setCenter(initialLocation);
infowindow.setContent(contentString);
infowindow.setPosition(initialLocation);
infowindow.open(map);
}, function() {
handleNoGeolocation(browserSupportFlag);
});
} else if (google.gears) {
// Try Google Gears Geolocation
browserSupportFlag = true;
var geo = google.gears.factory.create('beta.geolocation');
geo.getCurrentPosition(function(position) {
initialLocation = new google.maps.LatLng(position.latitude,position.longitude);
contentString = "Location found using Google Gears";
map.setCenter(initialLocation);
infowindow.setContent(contentString);
infowindow.setPosition(initialLocation);
infowindow.open(map);
}, function() {
handleNoGeolocation(browserSupportFlag);
});
} else {
// Browser doesn't support Geolocation
browserSupportFlag = false;
handleNoGeolocation(browserSupportFlag);
}
}
function handleNoGeolocation(errorFlag) {
if (errorFlag == true) {
initialLocation = newyork;
contentString = "Error: The Geolocation service failed.";
} else {
initialLocation = siberia;
contentString = "Error: Your browser doesn't support geolocation. Are you in Siberia?";
}
map.setCenter(initialLocation);
infowindow.setContent(contentString);
infowindow.setPosition(initialLocation);
infowindow.open(map);
}
</script>
</head>
<body onload="initialize()">
<div id="map_canvas"></div>
</body>
</html>
