W3C Geolocation API

Overview

• API for use in Web applications (through JavaScript binding)
• enables Web application running on a remote server to access user location (latitude/longitude) data; e.g., for a user accessing the Web from a browser running on a mobile device (mobile handset, laptop, etc.)

How does a Web app get access to user location data?

The API requires browser support; either the device a browser is running on must directly expose one or more location-sensing mechanisms (e.g., GPS) to the browser, or some other third-party application must expose it to the browser (e.g., WiFi positioning through SkyHook)

Who’s doing the work?

• W3C Geolocation Working Group
• the editor for the spec works for Google
• Google Gears has already shipped with support for the API

Where to get it

http://dev.w3.org/geo/api/spec-source.html

Requirements

• must provide location data in terms of a pair of latitude and longitude coordinates
• must provide information about the accuracy of the retrieved location data
• must support "one-shot" position updates

Requirements (more)

• must allow an application to register to receive repeated position updates
• must allow an application to cheaply query the last known position
• must provide a way for the application to receive updates about errors that may have occurred while obtaining a location fix

Requirements (more)

• must allow an application to specify a desired accuracy level of the location information
• must be agnostic to the underlying sources of location information
• should allow an application to request address information as part of the location data

Agnostic about location method

• The API does not expect or depend on any particular location method.
• Can work with any location-sensing mechanism exposed to the browser; might be on GPS, IP address, RFID, WiFi, Bluetooth MAC address, GSM/CDMA cell IDs,…

Some use cases

• Show the user's position on a map
• Find points of interest in the user's area
• Turn-by-turn route navigation (like NaviTime)
• Push alerts when points of interest are in the user's vicinity
• Location-tagged status updates in social networking applications

Example: “One-shot” query

  function showMap(position) {
    // Show a map centered at
    // at (position.latitude, position.longitude). }
  // One-shot position request.
  navigator.geolocation.getCurrentPosition(showMap);
    

Example: Position updates

  function scrollMap(position) {
    // Scrolls the map so it is centered
    // at (position.latitude, position.longitude). }
  // Request repeated updates.
  var watchId =
  navigator.geolocation.watchPosition(scrollMap);
  function buttonClickHandler() {
    // Cancel when user clicks button
    navigator.geolocation.clearWatch(watchId); }
    

IDL: Geolocation interface

  interface Geolocation { 
    readonly attribute Position lastPosition;
    void getCurrentPosition(in 
      PositionCallback successCallback);
    …
    int watchPosition(in
      PositionCallback successCallback);
    …
    void clearWatch(in int watchId); };

IDL: PositionCallback interface

  interface PositionCallback {
    void handleEvent(in Position position); };

IDL: Position object

  interface Position {
    readonly attribute double latitude;
    readonly attribute double longitude;
    readonly attribute double accuracy;
    readonly attribute double altitude;
    readonly attribute double altitudeAccuracy;
    readonly attribute double heading
    readonly attribute double velocity
    readonly attribute DOMTimeStamp timestamp; };
    

The End

Thanks!

mike@w3.org