This specification defines an API that provides scripted access to geographical location information associated with the hosting device.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the most recently formally published revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
If you wish to make comments regarding this document, please send them to public-geolocation@w3.org (subscribe, archives). All feedback is welcome.
Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation stage should join the aforementioned mailing list and take part in the discussions.
The Geolocation Working Group is responsible for this document. This is just an informal proposal at this time.
[If you keep the <!--comment--> the table of contents will be included here automatically.]
This section is non-normative.
The Geolocation API defines a high-level interface to location information associated with the hosting device, such as latitude and longitude. The API itself is agnostic of the underlying location information sources. Common sources of location information include Global Positioning System (GPS) and location inferred from network signals such as IP address, RFID, WiFi and Bluetooth MAC addresses, and GSM/CDMA cell IDs.
The API is designed to enable both "one-shot" position requests and repeated position updates, as well as the ability to explicitly query the cached positions. Location information is represented by latitude and longitude coordinates. The Geolocation API in this specification builds upon earlier work in the industry, including [AZALOC], [GEARSLOC], and [LOCATIONAWARE].
The following code extract illustrates how to obtain basic location information:
Example of a "one-shot" position request.
function showMap(position) {
// Show a map centered at (position.latitude, position.longitude).
}
// One-shot position request.
navigator.geolocation.getCurrentPosition(showMap);
Example of requesting repeated position updates.
function scrollMap(position) {
// Scrolls the map so that it is centered at (position.latitude, position.longitude).
}
// Request repeated updates.
var watchId = navigator.geolocation.watchPosition(scrollMap);
function buttonClickHandler() {
// Cancel the updates when the user clicks a button.
navigator.geolocation.clearWatch(watchId);
}
Example of requesting repeated position updates and handling errors.
function scrollMap(position) {
// Scrolls the map so that it is centered at (position.latitude, position.longitude).
}
function handleError(error) {
// Update a div element with error.message.
}
// Request repeated updates.
var watchId = navigator.geolocation.watchPosition(scrollMap, handleError);
function buttonClickHandler() {
// Cancel the updates when the user clicks a button.
navigator.geolocation.clearWatch(watchId);
}
Example of requesting a potentially cached position.
// Request a position. We accept positions whose age is not
// greater than 10 minutes. If the User Agent does not have a
// fresh enough cached position object, it will automatically
// acquire a new one.
navigator.geolocation.getCurrentPosition(successCallback,
errorCallback,
{maximumAge:600000});
function successCallback(position) {
// By using the 'maximumAge' option above, the position
// object is guaranteed to be at most 10 minutes old.
}
function errorCallback(error) {
// Update a div element with error.message.
}
Forcing the User Agent to return a fresh cached position.
// Request a position. We only accept cached positions whose age is not
// greater than 10 minutes. If the User Agent does not have a fresh
// enough cached position object, it will immediately invoke the error
// callback.
navigator.geolocation.getCurrentPosition(successCallback,
errorCallback,
{maximumAge:600000, timeout:0});
function successCallback(position) {
// By using the 'maximumAge' option above, the position
// object is guaranteed to be at most 10 minutes old.
// By using a 'timeout' of 0 milliseconds, if there is
// no suitable cached position available, the User Agent
// will immediately invoke the error callback with code
// TIMEOUT and will not initiate a new position
// acquisition process.
}
function errorCallback(error) {
switch(error.code) {
case error.TIMEOUT:
// Quick fallback when no suitable cached position exists.
doFallback();
// Acquire a new position object.
navigator.geolocation.getCurrentPosition(successCallback, errorCallback);
break;
case ... // treat the other error cases.
};
}
function doFallback() {
// No fresh enough cached position available.
// Fallback to a default position.
}
Forcing the User Agent to return any available cached position.
// Request a position. We only accept cached positions, no matter what
// their age is. If the User Agent does not have a cached position at
// all, it will immediately invoke the error callback.
navigator.geolocation.getCurrentPosition(successCallback,
errorCallback,
{maximumAge:Infinite, timeout:0});
function successCallback(position) {
// By setting the 'maximumAge' to Infinite, the position
// object is guaranteed to be a cached one.
// By using a 'timeout' of 0 milliseconds, if there is
// no cached position available at all, the User Agent
// will immediately invoke the error callback with code
// TIMEOUT and will not initiate a new position
// acquisition process.
if (position.timestamp < freshness_threshold &&
position.accuracy < accuracy_threshold) {
// The position is relatively fresh and accurate.
} else {
// The position is quite old and/or inaccurate.
}
}
function errorCallback(error) {
switch(error.code) {
case error.TIMEOUT:
// Quick fallback when no cached position exists at all.
doFallback();
// Acquire a new position object.
navigator.geolocation.getCurrentPosition(successCallback, errorCallback);
break;
case ... // treat the other error cases.
};
}
function doFallback() {
// No cached position available at all.
// Fallback to a default position.
}
This section is non-normative.
This specification is limited to providing a scripting APIs for retrieving geographic position information associated with a hosting device. The geographic position information is provided in terms of World Geodetic System coordinates [WGS84].
The scope of this specification does not include providing a markup language of any kind.
The scope of this specification does not include defining new URI schemes for building URIs that identify geographic locations.
The API defined in this specification can be used to retrieve the geographic location of a hosting device. In almost all cases, this information also discloses the location of the user of the device, thereby potentially compromising the user's privacy. A conforming implementation of this specification MUST provide a mechanism that protects the user's privacy and this mechanism SHOULD ensure that no location information is made available without the user's informed consent.
While the above wording reflects the current thinking of the Geolocation WG, there is a significant amount of debate on whether this specification should leave the details of the privacy protection mechanism entirely to the User Agent or whether it should also define a privacy framework that all conforming User Agents must implement. Please see the following threads:
All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]
Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.
Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)
User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
Implementations that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings defined in the Web IDL specification, as this specification uses that specification's terminology. [WEBIDL]
The Geolocation object can
be used by scripts to programmatically determine the location
information associated with the hosting device. The location
information is acquired by applying a user-agent specific algorithm,
creating a Position object, and
populating that object with appropriate data accordingly.
Objects implementing the Navigator interface
(e.g. the window.navigator object) must also implement
the NavigatorGeolocation
interface. [NAVIGATOR]. An instance
of NavigatorGeolocation would be then obtained by using
binding-specific casting methods on an instance
of Navigator.
[NoInterfaceObject]
interface NavigatorGeolocation {
readonly attribute Geolocation geolocation;
};
interface Geolocation {
void getCurrentPosition(in PositionCallback successCallback);
void getCurrentPosition(in PositionCallback successCallback, in PositionErrorCallback errorCallback);
void getCurrentPosition(in PositionCallback successCallback, in PositionErrorCallback errorCallback, in PositionOptions options);
int watchPosition(in PositionCallback successCallback);
int watchPosition(in PositionCallback successCallback, in PositionErrorCallback errorCallback);
int watchPosition(in PositionCallback successCallback, in PositionErrorCallback errorCallback, in PositionOptions options);
void clearWatch(in int watchId);
};
interface PositionCallback {
void handleEvent(in Position position);
};
interface PositionErrorCallback {
void handleEvent(in PositionError error);
};
The getCurrentPosition()
takes one, two or three arguments. When called, it must immediately
return and then asynchronously acquire a new Position object.
If successful, this method must invoke its associated
successCallback argument with a Position object as an argument. If the
attempt fails, and the method was invoked with a non-null
errorCallback argument, this method must invoke the
errorCallback with a PositionError object as an
argument.
The watchPosition()
takes one, two or three arguments. When called, it must immediately
return and then asynchronously start a watch process defined
as the following set of steps:
Position object.
If successful, invoke the associated successCallback with a Position object as an argument.
If the attempt fails, and the method was invoked with a non-null
errorCallback argument, this method must invoke the
errorCallback with a PositionError object as an
argument.
Position
object every time the implementation determines that the position
of the hosting device has changed.
This method returns an integer value that uniquely identifies the
watch process. When the clearWatch()
method is called with this identifier, the watch process must stop
acquiring any new position fixes and must cease invoking any callbacks.
The getCurrentPosition() and
watchPosition() methods
accept PositionOptions objects as
their third argument.
PositionOptions
objects are regular ECMAScript objects that have the following properties:
[NoInterfaceObject]
interface PositionOptions {
attribute boolean enableHighAccuracy;
attribute long timeout;
attribute long maximumAge;
};
The enableHighAccuracy, timeout
and maximumAge attributes are all optional.
The enableHighAccuracy
attribute provides a hint that the application would like to receive
the best possible results. This may result in slower response times
or increased power consumption. The user might also deny this
capability, or the device might not be able to provide more accurate
results than if the flag wasn't specified.
enableHighAccuracy is trying to solve.
The timeout attribute denotes
the maximum length of time (expressed in milliseconds) that is
allowed to pass from the the call to
getCurrentPosition() or watchPosition()
until the corresponding successCallback is invoked. If
the implementation is unable to successfully acquire a new Position
before the given timeout elapses, and no other errors have occurred
in this interval, then the corresponding errorCallback
must be invoked with a PositionError object whose code
attribute is set to TIMEOUT.
In case of a getCurrentPosition() call, the
errorCallback would be invoked exactly once.
In case of a watchPosition(), the
errorCallback could be invoked repeatedly: the first
timeout is relative to the moment watchPosition() was
called, while subsequent timeouts are relative to the moment when
the implementation determines that the position of the hosting
device has changed and a new Position object must be
acquired.
The maximumAge attribute
indicates that the application is willing to accept a cached
position whose age is no greater than the specified time in
milliseconds. If maximumAge is not specified or set to 0,
the implementation must immediately attempt to acquire a new
position object. Setting the maximumAge to Infinite
will force the implementation to return a cached position regardless
of its age. If an implementation does not have available a cached
position whose age is no greater than the
specified maximumAge, then it must acquire a new
position object. In case of a watchPosition(),
the maximumAge refers to the first position object
returned by the implementation.
interface Position {
readonly attribute double latitude;
readonly attribute double longitude;
readonly attribute double altitude;
readonly attribute double accuracy;
readonly attribute double altitudeAccuracy;
readonly attribute double heading;
readonly attribute double speed;
readonly attribute DOMTimeStamp timestamp;
};
The reference system used for the positioning attributes of this interface is the World Geodetic System [WGS84].
The latitude and longitude
attributes are specified in degrees.
The altitude attribute
denotes the height of the position, specified in meters above the [WGS84] ellipsoid. If the implementation cannot
provide altitude information, the value of this attribute must be
null.
The accuracy attribute
denotes the accuracy level of the latitude and longitude coordinates. It
is specified in meters and must be supported by all implementations.
The altitudeAccuracy attribute
is specified in meters. If the implementation cannot provide
altitude information, the value of this attribute must be null.
The accuracy and altitudeAccuracy
values returned by an implementation should correspond to a 95%
confidence level.
The heading attribute
denotes the direction of travel of the hosting device and is specified in
degrees counting clockwise relative to the true north. If the
implementation cannot provide heading information, the value of this
attribute must be null.
The speed attribute
denotes the current ground speed of the hosting device and is
specified in meters per second. If the implementation cannot
provide speed information, the value of this attribute must be
null.
The timestamp attribute
represents the time when the geographic location was acquired and is
represented as a DOMTimeStamp [DOMTIMESTAMP].
We are also debating whether we should include information
about civic addresses in the Position interface and
how this information could be acquired (e.g. via
reverse-geocoding). So far the agreement is to provide civic
address information in the second version of the Geolocation
API:
interface PositionError {
const unsigned short UNKNOWN_ERROR = 0;
const unsigned short PERMISSION_DENIED = 1;
const unsigned short POSITION_UNAVAILABLE = 2;
const unsigned short TIMEOUT = 3;
readonly unsigned short code;
readonly DOMString message;
};
The code attribute must return
the appropriate code from the following list:
UNKNOWN_ERROR (numeric value 0)PERMISSION_DENIED (numeric value 1)POSITION_UNAVAILABLE (numeric value 2)TIMEOUT (numeric value 3)The message attribute must
return an error message describing the details of the error
encountered. This attribute is primarily intended for debugging and
developers should not use it directly in their application user
interface.
Issue note: This section will get moved to a separate document
Someone visiting a foreign city could access a Web application that allows users to search or browse through a database of tourist attractions. Using the Geolocation API, the Web application has access to the user's approximate position and it is therefore able to rank the search results by proximity to the user's location.
A group of friends is hiking through the Scottish highlands. Some of them write short notes and take pictures at various points throughout the journey and store them using a Web application that can work offline on their hand-held devices. Whenever they add new content, the application automatically tags it with location data from the Geolocation API (which, in turn, uses the on-board GPS device). Every time they reach a town or a village, and they are again within network coverage, the application automatically uploads their notes and pictures to a popular blogging Web site, which uses the geolocation data to construct links that point to a mapping service. Users who follow the group's trip can click on these links to see a satellite view of the area where the notes were written and the pictures were taken. Another example is a life blog where a user creates content (e.g. images, video, audio) that records her every day experiences. This content can be automatically annotated with information such as time, geographic position or even the user's emotional state at the time of the recording.
A user is accessing an online service in order to arrange a parcel delivery and she needs to fill in a long form which includes special fields for her home address. To save the user's time, the application tries to pre-fill the address part of the form by using the Geolocation API to acquire the user's current location as a (latitude, longitude) pair as well as an address object. If an implementing User Agent cannot provide the address object, the application uses a third-party reverse geocoding service to translate the coordinates into a street address.
A user finds herself in an unfamiliar city area. She wants to check her position so she uses her hand-held device to navigate to a Web-based mapping application that can pinpoint her exact location on the city map using the Geolocation API. She then asks the Web application to provide driving directions from her current position to her desired destination.
Following from use-case 4, a mapping application can help the user navigate along a route by providing detailed turn-by-turn directions. The application does this by registering with the Geolocation API to receive repeated location updates of the user's position. These updates are delivered as soon as the implementing User Agent determines that the position of the user has changed, which allows the application to anticipate any changes of direction that the user might need to do.
A tour-guide Web application can use the Geolocation API to monitor the user's position and trigger visual or audio notifications when interesting places are in the vicinity. An online task management system can trigger reminders when the user is in the proximity of landmarks that are associated with certain tasks.
A widget-like Web application that shows the weather or news that are relevant to the user's current area can use the Geolocation API to register for location updates. If the user's position changes, the widget can adapt the content accordingly.
A social network application allows its users to automatically tag their status updates with location information. It does this by monitoring the user's position with the Geolocation API and using only certain parts from the Address object. Each user can control the granularity of the location information (e.g. city or neighbourhood level) that is shared with the other users. Any user can also track his network of friends and get real-time updates about their current location.
Alec Berntson, Steve Block, Greg Bolsinga, Aaron Boodman, Dave Burke, Chris Butler, Shyam Habarakada, Ian Hickson, Brad Lassey, Daniel Park, Stuart Parmenter, Olli Pettay, Chris Prince, Arun Ranganathan, Aza Raskin, Martin Thomson, Doug Turner, Mohamed Zergaoui