Internet Engineering Task Force (IETF) H. Schulzrinne Request for Comments: 5962 V. Singh Category: Standards Track Columbia University ISSN: 2070-1721 H. Tschofenig Nokia Siemens Networks M. Thomson Andrew Corporation September 2010
Dynamic Extensions to the Presence Information Data Format Location Object (PIDF-LO)
Abstract
The Geopriv Location Object introduced by the Presence Information Data Format - Location Object (PIDF-LO), RFC 4119, defines a basic XML format for carrying geographical information of a presentity. This document defines PIDF-LO extensions to convey information about moving objects. Elements are defined that enable expression of spatial orientation, speed, and heading of the presentity.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5962.
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
The Presence Information Data Format - Location Object (PIDF-LO) (see RFC 4119 [RFC4119]) provides geographical location of a presentity. This corresponds to a physical location at a given instance of time. RFC 5491 [RFC5491] extends PIDF-LO and provides additional guidelines to implementers.
This document extends PIDF-LO to convey spatial orientation, speed, and heading of a presentity. The addition of rate-of-change information to the PIDF-LO enables a range of use cases. These use cases either use dynamic information directly or use that information
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for smoother tracking of a position over time. For example, an application that continuously tracks a presentity could use velocity information to extrapolate positions in between times that location information is measured. A shipping company could directly use speed to monitor delivery truck speed to ensure speed limits are observed.
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [RFC2119].
This document uses the term "presentity", as defined in RFC 2778 [RFC2778], to refer to the device subject to location determination. The similarity to presence concepts and the abstract location privacy architecture, as described in RFC 4079 [RFC4079], led to re-use of the Presence Information Data Format (PIDF) (see RFC 3863 [RFC3863]), and its enhancement for location information (see RFC 4119 [RFC4119]). Note that this document does not differentiate between human and non-human objects, and hence both are in scope.
This document defines a new element, <Dynamic>, for the conveyance of dynamic information.
Dynamic information MAY be included without any other location information being present. When dynamic information is associated with information about the instantaneous position of the presentity, the <Dynamic> element MUST be included in the same <location-info> element as the corresponding geodetic (or civic) location information.
Dynamic information can be safely ignored by a recipient that does not support this specification. The <Dynamic> element contains the following components:
orientation:
The <orientation> element describes the spatial orientation of the presentity -- the direction that the object is pointing. For a device, this orientation might depend on the type of device. See Section 3.1 for details.
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speed:
Speed is the time rate of change in position of a presentity without regard for direction: the scalar component of velocity. The value for the <speed> element is a measure that is defined in meters per second.
heading:
Heading is the directional component of velocity. See Section 3.1 for details.
Each element can be omitted if no information is available. In the following example, the presentity is approximately oriented to the North at a slightly elevated angle. The presentity is travelling 24 meters per second to the West:
RFC 5962 Dynamic Extensions to PIDF-LO September 2010
Another example shows a PIDF-LO document of the presentity alice@example.com on a bike travelling 12 meters per second. Her position is indicated as a circle. The values for speed may be used by a receiver to adjust the uncertainty over time.
3.1. Angular Measures and Coordinate Reference Systems
[RFC5491] constrains the coordinate reference system (CRS) used in PIDF-LO to World Geodetic System 1984 (WGS 84), using either the two- dimensional (latitude, longitude) CRS identified by "urn:ogc:def:crs:EPSG::4326" or the three-dimensional (latitude, longitude, altitude) CRS identified by "urn:ogc:def:crs:EPSG::4979". Dynamic locations similarly assume that either of these coordinate reference systems will be used.
The <orientation> and <heading> elements both describe a direction. The <orientation> element describes the "direction of facing"; the <heading> element describes the "direction of travel". Both measures
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contain one or two angular values that are expressed relative to the current position of the presentity (see Appendix A). Angular measures are expressed in degrees, and values can be negative. If two measures are present, the values MUST be separated by whitespace.
The first measure specifies the horizontal direction from the current position of the presentity to a point that it is pointing towards (for <orientation>) or travelling towards (for <heading>). Horizontal angles are measured from Northing to Easting. Horizontal angles start from zero when pointing to or travelling towards the North and increase towards the East.
The second measure, if present, specifies the vertical component of this angle. This angle is the elevation from the local horizontal plane. If the second angle value is omitted, the vertical component is unknown. If only one angle is present, <orientation> describes only the horizontal component. For <heading>, the associated <speed> measure contains only the horizontal component of speed.
This document defines additional location elements carried by PIDF-LO. These additional elements provide greater reason to observe the privacy and security considerations described in RFC 4119 [RFC4119]. No further privacy or security measures are necessary.
RFC 4119 points back to RFC 3694 [RFC3694] and RFC 3693 [RFC3693] to describe the threat model and the security requirements imposed on the GEOPRIV architecture for sharing location information as a result of the threat model. It is important to note that these two documents often refer to threats related to the current location information of a presentity, while this document introduces dynamic information that may be used by attackers to anticipate the future location of a presentity. While already a series of location snapshots is likely to offer information for guessing the future location of a presentity, it has to be said that including more information in a PIDF-LO does increase the severity of an information leak. Those who deploy location-based services are in general strongly advised to provide their users with ways to control the distribution of location information to those who have been authorized to see it.
We would like to thank Klaus Darilion, Cullen Jennings, Rohan Mahy, Carl Reed, and Brian Rosen for their comments. Furthermore, we would like to thank Alexey Melnikov, Adrian Farrel, Tim Polk, Dan Romascanu for his IESG review comments, Avshalom Houri for his GenArt review, Hilarie Orman for her SECDIR review, and Joel Jaeggli for his Operations Directorate review.
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[RFC2778] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000.
[RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004.
[RFC3694] Danley, M., Mulligan, D., Morris, J., and J. Peterson, "Threat Analysis of the Geopriv Protocol", RFC 3694, February 2004.
[RFC3863] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004.
[RFC4079] Peterson, J., "A Presence Architecture for the Distribution of GEOPRIV Location Objects", RFC 4079, July 2005.
[RFC5491] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV Presence Information Data Format Location Object (PIDF-LO) Usage Clarification, Considerations, and Recommendations", RFC 5491, March 2009.
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Appendix A. Earth Centered, Earth Fixed Direction Vectors
The absolute orientation or heading of a presentity depends on its latitude and longitude. The following vectors can be used to determine the absolute direction in the WGS 84 Earth Centered, Earth Fixed (X, Y, Z) coordinate space.
The direction of North as a unit vector in Earth Centered, Earth Fixed (ECEF) coordinates is: