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Location Query This specification defines an XMPP protocol extension for querying a compliant server for information about the geographical or physical location of an entity." &LEGALNOTICE; 0255 Experimental Standards Track Standards Council XMPP Core NOT_YET_ASSIGNED Helge Timenes helge@buddycloud.com helge@buddycloud.com Simon Tennant simon@buddycloud.com simon@buddycloud.com Ross Savage ross@buddycloud.com ross@buddycloud.com 0.3 2008-12-20 ht
  • Corrected name-space in section 10.1.
  • Removed extra 's in example 7
  • Made time-stamp optional
  • Added optional time-stamp to beacon element
  • Added comment reflecting that query time-stamp applies to GPS coordinates if beacons provide own time-stamps
0.2 2008-12-17 ht
  • Updated examples to be conform with XEP-0080 (use lat and lon instead of latitude and longitude).
  • Fixed wrong closing tag for <type> in examples.
  • Added signal strength to beacon data.
0.1 2008-11-13 psa

Initial published version.

0.0.3 2008-11-07 ht
  • Removed <error/> child of geoloc element (arc minutes).
  • Added <accuracy/> (meters).
  • Updated notes on GPS data submitted in location query.
  • Replaced language encoding 'en-UK' with 'en-US' to avoid UK/GB confusion.
0.0.2 2008-11-03 ht
  • Corrected XML namespace.
  • Added country code reference.
0.0.1 2008-10-28 ht/st/rs

First draft.

This document defines a format for querying a location server for information about an entity's geographical location. The query must contain some location characteristics that the server can process to derive this information. These can be in the form of geodetic coordinates (from GPS receivers or other positioning equipment), in which case the server will perform "reversed geocoding" to derive the information. Alternatively, the location can be characterized by a list of identifiable radio transmitters (from here on called 'beacons') observable from this location. Typical beacons include cellular telephone towers, wireless network access points and bluetooth devices. In this case the location server must match the supplied characteristics with stored knowledge about the beacons to derive the submitting entity's location. Client implementers are encouraged to supply both kinds of characteristics when available, as this can be utilized by self-learning location servers. The location information returned by the location server is structured according to &xep0080;, ensuring compatibility with systems using this standard for location information publishing.

The location query is designed to be used as a one-shot request or as a continuous query-result dialogue. The latter form will allow location servers to analyze changes with time, which in most cases yields improved fidelity and the possibility to derive motion state information.

The format defined herein was designed to address the following requirements:

The basic principle behind this XMPP extension is as follows: An XMPP clients collects characteristics about its current location that is not directly suitable for presentation to a human user, but from which human readable location information can be derived. The client sends this information to a location server that derives this information and returns it to the querying client. Here "location server" means a XMPP server application that supports the locationquery stanza defined in this document. It can either be an integral part of the XMPP server, or run as a component on the same or a different machine from the XMPP server itself.

57.0501862 9.9188746 35.6 ]]> 1599-10-23T01:56:05Z 57.0501862 9.9188746 35.6 Jomfru Ane Gade 13 Aalborg Denmark http://shakespeare.lit/places/kings_head_pub_aalborg Near King's Head Pub ]]> 238:02:34775:50880 cell 00:0F:3D:42:92:2A wifi 00:19:CB:45:50:4A wifi ]]> 1599-10-23T01:56:05Z 57.050122 9.918833 Aalborg Jomfru Ane Gade 13 Denmark 20 http://shakespeare.lit/places/kings_head_pub_aalborg King's Head Pub ]]> 1599-10-23T01:55:21Z 57.0501862 9.918874 33.56 true 238:02:34775:50880 cell -88 1599-10-23T01:55:21Z 238:02:34775:48770 cell -76 1599-10-23T01:52:34Z 00:0F:3D:42:92:2A wifi -64 1599-10-23T01:55:21Z 238:02:34775:50880 cell -88 1599-10-23T01:55:21Z 00:19:CB:45:50:4A wifi -82 1599-10-23T01:52:24Z 00:18:42:E6:71:51 bluetooth ]]> ]]> 1599-10-23T01:56:05Z 57.0501862 9.918874 Jomfru Ane Gade 13 Aalborg Denmark 20 http://shakespeare.lit/places/kings_head_pub_aalborg King's Head Pub ]]> 1599-10-23T01:56:05Z 57.0501862 9.918874 Jomfru Ane Gade 13 Aalborg Denmark 20 http://shakespeare.lit/places/kings_head_pub_aalborg King's Head Pub 1599-10-23T01:56:05Z 57.0501862 9.918874 Jomfru Ane Gade 13 Aalborg Denmark 20 http://shakespeare.lit/places/kings_head_pub_aalborg King's Head Pub ]]>

Information about the radio beacons in the entity's surrounding, and its geodetic coordinates are provided by the entity and propagated on the network by the entity's associated application (usually a client). The information is structured by means of a <locationquery/> element that is qualified by the 'urn:xmpp:locationquery:0' namespace and nested with in a <iq> element with type set to get. The location result is provided by the location server and returned to the client in a <iq> element with type set to result. The location result is structured by means of a <geoloc/> element that is qualified by the 'http://jabber.org/protocol/geoloc' namespace (see XEP-0080).

Element Name Datatype Definition Example Notes
timestamp xs:datetime UTC time-stamp (MUST conform to the DateTime profile of &xep0082;). 2004-02-19T21:12Z Optional. If individual beacons contain own timing information, this time-stamp shall represent GPS time only, otherwise it shall represent all provided info in the query. If not set, the server may assume current time.
publish xs:boolean A flag specifying whether or not the server should publish the location result to subscribers of the submitting user's XEP-0080 compatible geoloc pub-sub node instead of returning it directly to the submitting user. true Optional. If present and "true", the server shall publish the entity's location details whenever it changes (suitable for periodic queries) and respond to the query with an empty <iq> stanza with type set to "result". If not specified or "false" the server shall return the location results to the submitting user in the form of a geoloc stanza (XEP-0080) embedded in a <iq> with type set to "result". Default is "false"
lat xs:decimal Latitude in decimal degrees North. 39.75 Required if no radio beacon data present, otherwise optional. If present, this shall also be present in the result stanza. If not present, the location server SHOULD estimate a value based on submitted beacon data and return with result stanza. The location server is free to decide if the value of this field should be piped directly through to result, or if it should be modified based on beacon data or time history information. For instance: if the entity is indoors, the GPS signal will be inaccurate and unstable over time. If wifi beacons are submitted, the location server may decide that the entity is inside a known building, and return the latitude of this instead.
lon xs:decimal Longitude in decimal degrees East -104.99 See notes for lat
alt xs:decimal Altitude in meters above or below sea level 1609 Optional. If present, this shall also be present in the result stanza with identical value.
bearing xs:decimal GPS bearing (direction in which the entity is heading to reach its next waypoint), measured in decimal degrees relative to true north See notes for alt
datum xs:string GPS datum (See XEP-0080) See notes for alt
accuracy xs:decimal Horizontal GPS accuracy in meters 10 See notes for lat
speed xs:decimal The speed at which the entity is moving, in meters per second 52.69 See notes for alt
beacons locationquery:beacon A list of identifiable radio transmitters observed by the entity Required if no lat and lon values specified, otherwise optional. See Table 2 for type definition.
Element Name Datatype Definition Example Notes
id xs:string A world-wide unique beacon identifier. This SHALL be composed as follows:

For cell towers: "MCC:MNC:LAC:CID" where MCC is the mobile country code Values of Mobile Country Codes (MCC) are specified by Annex to ITU Operational Bulletin No. 897 – 1.XII.2007.), MNC is the network carrier code, LAC is the area code and CID is the cell ID.

For wireless access points and bluetooth devices: The device MAC address.
207:02:12643:78596 Required
type xs:string Beacon type. One of "cell", "wifi", "bluetooth", "wimax", "rfid" (?), "other" "cell" Required.
signalstrength xs:int Beacon signal strength in dBM. -64 Optional.
timestamp xs:datetime UTC time-stamp (MUST conform to the DateTime profile of &xep0082;). 2004-02-19T21:12Z Optional. If query contains info from multiple beacon scans, specifying the timestamp for each beacon may lead to improved temporal analysis (movement state etc).
Element Name Datatype Definition Example Notes
alt xs:decimal Altitude in meters above or below sea level 1609 Piped directly through from query alt field if set.
area xs:string A named area such as a campus or neighborhood Central Park
bearing xs:decimal GPS bearing (direction in which the entity is heading to reach its next waypoint), measured in decimal degrees relative to true north Piped directly through from query bearing field if set.
building xs:string A specific building on a street or in an area The Empire State Building
country xs:string The nation where the user is located USA
datum xs:string GPS datum (See notes for XEP-0080) Piped directly through from query datum field if set.
description xs:string A natural-language name for or description of the location Bill's house If location is mapped to a place in a place oriented service, this should hold the place description.
accuracy xs:decimal Horizontal GPS accuracy in meters 10 Piped directly through from query accuracy field or estimated by location server using based on the other information in query and, if possible, differences between several queries over time.
floor xs:string A particular floor in a building 102
lat xs:decimal Latitude in decimal degrees North 39.75 Piped directly through from query lat field or estimated by location server based on the other information in query and, if possible, differences between several queries over time.
locality xs:string A locality within the administrative region, such as a town or city New York City
lon xs:decimal Longitude in decimal degrees East -104.99 Piped directly through from query lon or estimated by location server based on the other information in query and, if possible, differences between several queries over time.
postalcode xs:string A code used for postal delivery 10027
region xs:string An administrative region of the nation, such as a state or province New York
room xs:string A particular room in a building Observatory
speed The speed at which the entity is moving, in meters per second 52.69 xs:decimal Piped directly through from query speed field or estimated by location server based on the other information in query and, if possible, differences between several queries over time.
street xs:string A thoroughfare within the locality, or a crossing of two thoroughfares 34th and Broadway
text xs:string A catch-all element that captures any other information about the location Northwest corner of the lobby Best practice tip: This field can be used by the server to combine several fields in a natural language style, suitable for simple one-line location presence text. Example: "Near Bob's place" (description + accuracy), "On the road in New York" (locality + speed)
timestamp xs:datetime UTC timestamp specifying the moment when the reading was taken (MUST conform to the DateTime profile of XEP-0082) 2004-02-19T21:12Z Piped directly through from query timestamp field.
uri A URI or URL pointing to information about the location http://beta.plazes.com/plazes/1940:jabber_inc xs:anyURI Only applicable to place-oriented services

NOTE: The datatypes specified above are defined in &w3xmlschema2;.

The location results SHOULD be distributed means of &xep0060; or the subset thereof specified in &xep0163;. This can be done automatically by requesting the "publish" location query result format, in which case the location server will publish the results on the user's behalf. Alternatively the it can be done client side as outlined in XEP-0080.

The does not have to determine a value for all fields of the <geoloc> stanza, but it SHOULD determine values for as many as possible. At the very least a value for 'country' should be set.

If no GPS coordinate and accuracy information is submitted in the query, and the server determines location coordinates from submitted beacon data, a value for the returned geoloc 'accuracy' field SHOULD be returned. The magnitude of this should be derived based on the ranges of the beacons used to determine the location.

The server should make no assumptions about how often a entity submits a query. It should support occasional manually triggered queries as well as periodic automated queries. In the latter case it should analyze changes over time, as this can greatly increase the fidelity of the result.

Furthermore, no assumptions should be made about the number of beacons being logged in each query. Some handset manufacturers limit the access programmers have to cell tower and access point information. Some may only offer the currently connected cell ID, such that even if the handset can "see" many cell towers, only the one to which the handset is connected at the moment can be read. In this case the cell tower readings may not be constant, even if the querying entity is not moving. Rather it may jump round-robin style to each visible cell with variable time spent on each. The location server should account for this to avoid yielding results indicating that a user is running around in cell-sized circles when he is in fact stationary. Again, analysis of variation of submitted queries over time is recommended.

As no guarantees can be made that a given radio beacon stays at one fixed physical location throughout it's lifetime, the server should implement means to detect this. Generally it can be assumed that cell towers seldom move (could happen when a network operator changes the way it allocates cell IDs or when a tower is physically moved to a different location). Wireless access points move a bit more frequently (for instance when their owners move, or if they are installed in moving vehicles such as busses or trains). Bluetooth devices can generally be assumed to be mobile and should, unless specific knowledge to the contrary exists, not be used to locate an entity to a specific physical location. Rather, bluetooth devices (and other mobile beacons) can be used to co-locate entities to other entities for which a physical location is known. An example: Entity A submits query with GPS coordinates and the ID of some bluetooth device. It is located based on its submitted coordinates. Entity B submits a query with the same bluetooth device ID, but no GPS coordinates. Given this, and the fact that bluetooth transmitters have a very limited range, the server can then derive that A and B are at the same physical location (it may add 10-20 m to the accuracy of the location of B to account for the bluetooth range).

The "radio landscape" is by no means constant. New beacons are added continuously, and old ones are phased out. A location server will have to adapt to this shifting landscape, either by means of operator-supplied databases (in case of cell towers) or by means of user generated information. This standard was written with the latter in mind, and it is recommended that location servers utilize any queries with combined GPS and radio beacon information to "learn" the approximate physical location of the provided beacons. For server implementation that rely on user generated information only, it is also recommended to supply additional means for the users to feed back location context in cases where the client does not have any GPS access, or when the server produces the wrong results. One way to do this would be to let the users define "placemarks" (a name, street, city etc) that can be associated with the beacons seen by this user at the time of definition. This is however beyond the scope of this XEP.

For the reasons mentioned above, it is recommended that the client supply both GPS coordinates as well as nearby radio beacon information when possible. Also it is recommended that the client submit queries frequently enough to allow the server to analyze changes over time (or lack thereof) to obtain a better result. When possible, the client should include wifi access points in the queries, as these yield much more precise results than cell towers alone (due to the much more limited range). This must however all be weighted against the increased power consumption resulting from keeping network sockets open, scanning for access points and driving a GPS receiver.

For optimal results, clients SHOULD post a location query any time when the set of observed beacons change (a new beacon is seen or an old one is not seen any more)

Because the character data contained in the location results is intended to be readable by humans, the location query SHOULD possess an 'xml:lang' attribute specifying the natural language of such character data &rfc4646;. If so, the server SHOULD equip the <geoloc/> element, of the result stanza with an identical attribute

It is imperative to control access to location information, at least by default. Imagine that a stalker got unauthorized access to this information, with enough accuracy and timeliness to be able to find the target person. This scenario could lead to loss of life, so please take access control checks seriously. If an error is deliberately added to a location, the error SHOULD be the same for all receivers, to minimize the likelihood of triangulation. In the case of deliberate error, the <accuracy/> element SHOULD NOT be included.

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [7].

This specification defines the following XML namespace:

  • urn:xmpp:locationquery:0

Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespaces to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.

If the protocol defined in this specification undergoes a major revision that is not fully backward-compatible with an older version, or that contains significant new features, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.

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Schema for the location results are given by XEP-0080.