Geolocation

SE-2840 Dr. Mark L. Hornick 1

GeolocationWherever you go, there you are

What is Geolocation? Built-in browser functionality that lets you

make a web application location-aware Geographic latitude/longitude

Supported by all modern browsers Geolocation services are part of the

HTML5/W3C JavaScript API


What can you do with Geolocation? Show user’s position on a map Indicate proximity to hospitals, coffee shops,

public transit… Provide directions to a known point of interest Alert users to friends in the area Notify users of events, traffic, local weather… Provide auto-assist for zip code, area code,

shipping costs…


How does the browser know your location?

First, the browser must obtain your consent to use your location This security mechanism is built-in and cannot be

disabled (part of HTML5 specification)

Next, the browser gathers information from your computer Collected info is sent to the default location service

provider (Google Location Services) to get an estimate of your location


Location on stationary “desktop” computers

Location information generally available to the browser is limited to the IP address supplied by your ISP Universally available on any computer

Often resolves to your ISP’s office location, so accurate only to a neighborhood or city

Limits what you can do with the information Local weather forecast Default language to present to user


Wifi-based geolocation Google (and others) have an extensive

database of wifi networks that were collected as part of the Google Maps project

If multiple wifi hotspots are available, triangulation based on signal strength can be used to determine location to ~100 ft

Relies on accuracy of the databaseSE-2840 Dr. Mark L. Hornick 6

Cellphone-based geolocation Cell towers report their geographical location

to the device using the tower

When multiple cell towers are available, triangulation based on signal strength can be used to determine location Fairly accurate (~100ft) Works indoors and outdoors

In (rural) areas with few cell towers, accuracy is poor


GPS-based geolocation Device hosting the browser contains

hardware that receives signals from multiple GPS satellites in geosynchronous orbit Can be highly accurate (~3ft) Available everywhere Works outdoors only – view of sky required Accuracy decreases in areas with tall buildings,

forests, cloudy skies, sunspot activity


How do you select which method your browser will use? You don’t – the browser will decide internally

how it is going to determine your location.

However, you can specify how accurate you want the answer to be The browser may communicate with your device

to prompt you to enable GPS (if you have it) to get you a more accurate estimate of your location.



BOM implementation: Geolocation services are part of the navigator child object of the window object

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The geolocation API methods are implemented in the navigator object.

If geolocation is not supported, the navigator object will not have a geolocation child object.

geolocation

Geolocation JavaScript API:getting your location

One-time position request:if( navigator.geolocation ) {// check for geolocation support navigator.geolocation.getCurrentPosition( displayLoc );} else { // no geolocation object in BOM navigator

alert(“No geolocation support!”);}

...// This function is called when the location is foundfunction displayLoc( position ) {

var lat = position.coords.latitude;var long = position.coords.longitude;// TODO: display the position somewhere on the page

}SE-2840

Dr. Mark L. Hornick12

getCurrentPosition() details – handling errors

getCurrentPosition takes 1, 2, or 3 arguments:getCurrentPosition( successHandler,

/* optional */ errorHandler, /* optional */ positionOptions);

// This function is called when an error occurs:function errorHandler( error ) {

// error.code is a value from 0 – 3:// 0: unknown error// 1: Permission denied by user// 2: position not available// 3: request timed out

// if the error code is 0 or 2, error.message may // contain a more specific reason for the failure} SE-2840

Dr. Mark L. Hornick13

Geolocation JavaScript APIwatching your location change

Periodic update position request:if( navigator.geolocation ) {// check for geolocation support wID = navigator.geolocation.watchPosition( displayLoc );} else { // no geolocation object in BOM navigator

alert(“No geolocation support!”);}// Call this function to cancel the watchfunction stopWatch() {

if( wID ) { // make sure wID is not nullnavigator.geolocation.clearWatch( wID );wID = null;

}}

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positionOptions details – changing how often your location is updated

Both getCurrentPosition and watchPosition take an optional 3rd PositionOptions argument.getCurrentPosition( successHandler,

/* optional */ errorHandler, /* optional */ positionOptions);

// The positionOptions argument is a map:var positionOptions {

enableHighAccuracy: true, // favor accuracy over speedtimeout: Infinity, // ms to wait for pos valuemaximumAge: 0 // ms age of cached pos; 0=get new

pos}

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Integration with Google Maps:displaying a map using acquired coordinates

<script src="http://maps.google.com/maps/api/js?sensor=true"></script>function displayMap(position) { // display a Google Map

var googlePosition = new google.maps.LatLng(position.coords.latitude,

position.coords.longitude); var mapOptions = { zoom: 10, // range 0 to 21 center: googlePosition, // location of center of map mapTypeId: google.maps.MapTypeId.ROADMAP // ROADMAP,

SATELLITE, or HYBRID };

var mapDiv = $("#map").get(0); // get the DOM <div> element var map = new google.maps.Map(mapDiv, mapOptions);

}


Integration with Google Maps:displaying marker (push-pin) on the map

function addMarker(map, position, title, content) { var markerOptions = { position: position, // position of the push-pin map: map,// the map to put the pin into title: title, // title of the pin clickable: true // enable info window pop-up }; var marker = new google.maps.Marker(markerOptions); }


Integration with Google Maps:displaying location information in a pop-up

function addMarker(map, position, title, content) { … var marker = new google.maps.Marker(markerOptions);

var infoWindowOptions = { content: content, // description in pop-up position: position // where to put it }; var infoWindow = new

google.maps.InfoWindow(infoWindowOptions); google.maps.event.addListener(marker, "click", function() { infoWindow.open(map); }); }


Documents

Geolocation