Internet Engineering Task Force (IETF) M. Thomson Request for Comments: 7035 Microsoft Category: Standards Track B. Rosen ISSN: 2070-1721 Neustar D. Stanley Aruba Networks G. Bajko Nokia A. Thomson Lookingglass October 2013
Relative Location Representation
Abstract
This document defines an extension to the Presence Information Data Format Location Object (PIDF-LO) (RFC 4119) for the expression of location information that is defined relative to a reference point. The reference point may be expressed as a geodetic or civic location, and the relative offset may be one of several shapes. An alternative binary representation is described.
Optionally, a reference to a secondary document (such as a map image) can be included, along with the relationship of the map coordinate system to the reference/offset coordinate system, to allow display of the map with the reference point and the relative offset.
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/rfc7035.
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Copyright Notice
Copyright (c) 2013 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.
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Table of Contents
1. Introduction ....................................................4 2. Conventions Used in This Document ...............................4 3. Overview ........................................................4 4. Relative Location ...............................................7 4.1. Relative Coordinate System .................................8 4.2. Placement of XML Elements ..................................8 4.3. Binary Format ..............................................9 4.4. Distances and Angles .......................................9 4.5. Value Encoding ............................................10 4.6. Relative Location Restrictions ............................10 4.7. Baseline TLVs .............................................10 4.8. Reference TLVs ............................................10 4.9. Shapes ....................................................11 4.9.1. Point ..............................................11 4.9.2. Circle or Sphere Shape .............................12 4.9.3. Ellipse or Ellipsoid Shape .........................13 4.9.4. Polygon or Prism Shape .............................15 4.9.5. Arc-Band Shape .....................................18 4.10. Dynamic Location TLVs ....................................20 4.10.1. Orientation .......................................20 4.10.2. Speed .............................................20 4.10.3. Heading ...........................................20 4.11. Secondary Map Metadata ...................................21 4.11.1. Map URL ...........................................21 4.11.2. Map Coordinate Reference System ...................21 4.11.3. Map Example .......................................24 5. Examples .......................................................24 5.1. Civic PIDF with Polygon Offset ............................24 5.2. Geo PIDF with Circle Offset ...............................26 5.3. Civic TLV with Point Offset ...............................27 6. Schema Definition ..............................................28 7. Security Considerations ........................................30 8. IANA Considerations ............................................31 8.1. Relative Location Registry ................................31 8.2. URN Sub-Namespace Registration ............................33 8.3. XML Schema Registration ...................................33 8.4. Geopriv Identifiers Registry ..............................34 8.4.1. Registration of Two-Dimensional Relative Coordinate Reference System URN ....................35 8.4.2. Registration of Three-Dimensional Relative Coordinate Reference System URN ....................35 9. Acknowledgements ...............................................35 10. References ....................................................36 10.1. Normative References .....................................36 10.2. Informative References ...................................38
This document describes a format for the expression of relative location information.
A relative location is formed of a reference location plus a relative offset from that reference location. The reference location can be represented in either civic or geodetic form. The reference location can also have dynamic components such as velocity. The relative offset is specified in meters using a Cartesian coordinate system.
In addition to the relative location, an optional URI can be provided to a document that contains a map, floor plan, or other spatially oriented information. Applications could use this information to display the relative location. Additional fields allow the map to be oriented and scaled correctly.
Two formats are included: an XML form that is intended for use in PIDF-LO [RFC4119] and a TLV format for use in other protocols such as those that already convey binary representation of location information defined in [RFC4776].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This document describes an extension to PIDF-LO [RFC4119] as updated by [RFC5139] and [RFC5491], to allow the expression of a location as an offset relative to a reference.
Reference Location o \ \ Offset \ _\| x Relative Location
This extension allows the creator of a location object to include two location values plus an offset. The two location values, named "baseline" and "reference", combine to form the origin of the offset.
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The final, relative location is described relative to this reference point.
The baseline location is included outside of the <relative-location> element. The baseline location is visible to a client that does not understand relative location (i.e., it ignores the <relative-location> element).
A client that does understand relative location will interpret the location within the relative element as a refinement of the baseline location. This document defines both a reference location, which serves as a refinement of the baseline location and the starting point, and an offset, which describes the location of the Target based on this starting point.
Creators of location objects with relative location thus have a choice of how much information to put into the baseline location and how much to put into the reference location. For example, the baseline location value could be precise enough to specify a building that contains the relative location, and the reference location could specify a point within the building from which the offset is measured.
Location objects SHOULD NOT have all location information in the baseline location. Doing this would cause clients that do not understand relative location to incorrectly interpret the baseline location (i.e., the reference point) as the actual, precise location of the client. The baseline location is intended to carry a location that encompasses both the reference location and the relative location (i.e., the reference location plus offset).
It is possible to provide a valid relative location with no information in the baseline. However, this provides recipients who do not understand relative location with no information. A baseline location SHOULD include sufficient information to encompass both the
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reference and relative locations while providing a baseline that is as accurate as possible.
Both the baseline and the reference location are defined as either a geodetic location [OGC.GeoShape] or a civic address [RFC4776]. If the baseline location was expressed as a geodetic location, the reference MUST be geodetic. If the baseline location was expressed as a civic address, the reference MUST be civic.
Baseline and reference locations MAY also include dynamic location information [RFC5962].
The relative location can be expressed using a point (2- or 3-dimensional) or a shape that includes uncertainty: circle, sphere, ellipse, ellipsoid, polygon, prism, or arc-band. Descriptions of these shapes can be found in [RFC5491].
Optionally, a reference to a 'map' document can be provided. The reference is a URI [RFC3986]. The document could be an image or dataset that represents a map, floor plan, or other form. The type of document the URI points to is described as a MIME media type [RFC2046]. Metadata in the relative location can include the location of the reference point in the map as well as an orientation (angle from North) and scale to align the document Coordinate Reference System (CRS) with the World Geodetic System 1984 (WGS84) [WGS84] CRS. The document is assumed to be usable by the application receiving the PIDF with the relative location to locate the reference point in the map. This document does not describe any mechanisms for displaying or manipulating the document other than providing the reference location, orientation, and scale.
As an example, consider a relative location expressed as a point, relative to a civic location:
Relative location is a shape (e.g., point, circle, ellipse). The shape is defined with a CRS that has a datum defined as the reference (which appears as a civic address or geodetic location in the tuple) and the shape coordinates as meter offsets North/East of the datum measured in meters (with an optional Z offset relative to datum altitude). An optional angle allows the reference CRS be to rotated with respect to North.
The relative coordinate reference system uses a coordinate system with two or three axes.
The baseline and reference locations are used to define a relative datum. The reference location defines the origin of the coordinate system. The centroid of the reference location is used when the reference location contains any uncertainty.
The axes in this coordinate system are originally oriented based on the directions of East, North, and Up from the reference location: the first (x) axis increases to the East, the second (y) axis points North, and the optional third (z) axis points Up. All axes of the coordinate system use meters as a basic unit.
Any coordinates in the relative shapes use the described Cartesian coordinate system. In the XML form, this uses a URN of "urn:ietf:params:geopriv:relative:2d" for two-dimensional shapes and "urn:ietf:params:geopriv:relative:3d" for three-dimensional shapes. The binary form uses different shape type identifiers for 2D and 3D shapes.
Dynamic location information [RFC5962] in the baseline or reference location alters the relative coordinate system. The resulting Cartesian coordinate system axes are rotated so that the y axis is oriented along the direction described by the <orientation> element. The coordinate system also moves as described by the <speed> and <heading> elements.
The single timestamp included in the tuple (or equivalent) element applies to all location elements, including all three components of a relative location: baseline, reference, and relative. This is particularly important when there are dynamic components to these items. A location generator is responsible for ensuring the consistency of these fields.
The baseline of the reference location is represented as <location-info> like a normal PIDF-LO. Relative location adds a new <relative-location> element to <location-info>. Within <relative-location>, <reference> and <offset> elements are described. Within <offset> are the shape elements described below. This document extends PIDF-LO as described in [RFC6848].
This document describes a way to encode the relative location in a binary TLV form for use in other protocols that use TLVs to represent location.
A type-length-value encoding is used.
+------+------+------+------+------+------+------+ | Type |Length| Value ... +------+------+------+------+------+------+------+ | T | N | Value ... +------+------+------+------+------+------+------+
Figure 1: TLV Tuple Format
The Type field (T) is an 8-bit unsigned integer. The type codes used are registered in an IANA-managed "Relative Location Parameters" registry defined by this document and restricted to not include the values defined by the "Civic Address Types (CAtypes)" registry. This restriction permits a location reference and offset to be coded within the same object without type collisions.
The Length field (N) is defined as an 8-bit unsigned integer. This field can encode values from 0 to 255. The length field describes the number of bytes in the Value. Length does not count the bytes used for the Type or Length.
The Value field is defined separately for each type.
Each element of the relative location has a unique TLV assignment. A relative location encoded in TLV form includes both baseline and reference location TLVs and relative location TLVs. The reference TLVs are followed by the relative offset and optional map TLVs described in this document.
All distance measures used in shapes are expressed in meters.
All orientation angles used in shapes are expressed in degrees. Orientation angles are measured from WGS84 Northing to Easting with zero at Northing. Orientation angles in the relative coordinate system start from the second coordinate axis (y or Northing) and increase toward the first axis (x or Easting).
The binary form uses single-precision floating-point values [IEEE.754] to represent coordinates, distance, and angle measures. Single-precision values are 32-bit values with a sign bit, 8 exponent bits, and 23 fractional bits. This uses the interchange format defined in [IEEE.754] and Section 3.6 of [RFC1014], that is: sign, biased exponent and significand, with the most significant bit first.
Binary-encoded coordinate values are considered to be a single value without uncertainty. When encoding a value that cannot be exactly represented, the best approximation MUST be selected according to [Clinger1990].
More than one relative shape MUST NOT be included in either a PIDF-LO or TLV encoding of location for a given reference point.
Any error in the reference point transfers to the location described by the relative location. Any errors arising from an implementation not supporting or understanding elements of the reference point directly increases the error (or uncertainty) in the resulting location.
When a reference is encoded in binary form, the baseline and reference locations are combined in a reference TLV. This TLV is identified with the code 111 and contains civic address TLVs (if the baseline was a civic) or geo TLVs (if the baseline was a geo).
Shape data is used to represent regions of uncertainty for the reference and relative locations. Shape data in the reference location uses a WGS84 [WGS84] CRS. Shape data in the relative location uses a relative CRS.
The XML form for shapes uses Geography Markup Language (GML) [OGC.GML-3.1.1], consistent with the rules in [RFC5491]. Reference locations use the CRS URNs specified in [RFC5491]; relative locations use either a 2D CRS ("urn:ietf:params:geopriv:relative:2d") or a 3D ("urn:ietf:params:geopriv:relative:3d"), depending on the shape type.
The binary form of each shape uses a different shape type for 2D and 3D shapes.
Where "$CRS-URN$" is replaced by a "urn:ietf:params:geopriv:relative:2d" or "urn:ietf:params:geopriv:relative:3d" and "$Coordinate-3$" is omitted if the CRS is two-dimensional.
A circle or sphere describes a single point with a single uncertainty value in meters.
In a two-dimensional CRS, the coordinate includes two values, and the resulting shape forms a circle. In a three-dimensional CRS, the coordinate includes three values, and the resulting shape forms a sphere.
An ellipse or ellipsoid describes a point with an elliptical or ellipsoidal uncertainty region.
In a two-dimensional CRS, the coordinate includes two values plus a semi-major axis, a semi-minor axis, a semi-major axis orientation (clockwise from North). In a three-dimensional CRS, the coordinate includes three values, and in addition to the two-dimensional values, an altitude uncertainty (semi-vertical) is added.
A polygon or prism includes a number of points that describe the outer boundary of an uncertainty region. A prism also includes an altitude for each point and prism height.
At least 3 points MUST be included in a polygon. In order to interoperate with existing systems, an encoding SHOULD include 15 or fewer points, unless the recipient is known to support larger numbers.
Alternatively, a series of <pos> elements can be used in place of the single "posList". Each <pos> element contains two or three coordinate values.
Note that the first point is repeated at the end of the sequence of coordinates and no explicit count of the number of points is provided.
A GML polygon that includes altitude cannot be represented perfectly in TLV form. When converting to the binary representation, a two- dimensional CRS is used, and altitude is removed from each coordinate.
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A prism is represented in and converted from GML using the following template:
A polygon containing 2D points uses a type code of 119. A polygon with 3D points uses a type code of 120. A prism uses a type code of 121. The number of points can be inferred from the length of the TLV.
Note that unlike the polygon representation in GML, the first and last points are not the same point in the TLV representation. The duplicated point is removed from the binary form.
An arc-band describes a region constrained by a range of angles and distances from a predetermined point. This shape can only be provided for a two-dimensional CRS.
Distance and angular measures are defined in meters and degrees, respectively. Both are encoded as single-precision floating-point values.
The optional "map" URL can be used to provide a user of relative location with a visual reference for the location information. This document does not describe how the recipient uses the map nor how it locates the reference or offset within the map. Maps can be simple images, vector files, 2D or 3D geospatial databases, or any other form of representation understood by both the sender and recipient.
In XML, the map is a <map> element defined within <relative-location> and contains the URL. The URL is encoded as a UTF-8-encoded string. An "http:" [RFC2616] or "https:" [RFC2818] URL MUST be used unless the entity creating the PIDF-LO is able to ensure that authorized recipients of this data are able to use other URI schemes. A "type" attribute MUST be present and specifies the kind of map the URL points to. Map types are specified as MIME media types as recorded in the IANA Media Types registry, for example, <map type="image/png"> https://www.example.com/floorplans/123South/floor-2</map>.
In binary, the map type is a separate TLV from the map URL. The media type uses a type code of 126; the URL uses a type code of 127.
+------+------+------+------+------+------+------+ | 126 |Length| Map Media Type ... +------+------+------+------+------+------+------+ | 127 |Length| Map Image URL ... +------+------+------+------+------+------+------+
Figure 19: Map URL TLVs
Note that the binary form restricts data to 255 octets. This restriction could be problematic for URLs in particular. Applications that use the XML form, but cannot guarantee that a binary form won't be used, are encouraged to limit the size of the URL to fit within this restriction.
The CRS used by the map depends on the type of map. For example, a map described by a 3-D geometric model of the building may contain a complete CRS description in it. For some kinds of maps, typically described as images, the CRS used within the map must define the following:
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o The CRS origin
o The CRS axes used and their orientation
o The unit of measure used
This document provides elements that allow for a mapping between the local coordinate reference system used for the relative location and the coordinate reference system used for the map where they are not the same.
This optional element identifies the coordinates of the reference point as it appears in the map. This value is measured in a map- type-dependent manner, using the coordinate system of the map.
For image maps, coordinates start from the upper left corner, and coordinates are first counted by column with positive values to the right; then, rows are counted with positive values toward the bottom of the image. For such an image, the first item is columns, the second rows, and any third value applies to any third dimension used in the image coordinate space.
The <offset> element contains 2 (or 3) coordinates similar to a GML <pos>. For example:
If omitted, a value containing all zeros is assumed. If the coordinates provided contain fewer values than are needed, the first value from the set is applied in place of any absent values. Thus, if a single value is provided, that value is used for Coordinate-2
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and Coordinate-3 (if required). If two values are provided and three are required, the value of Coordinate-1 is used in place of Coordinate-3.
The map orientation includes the orientation of the map direction in relation to the Earth. Map orientation is expressed relative to the orientation of the relative coordinate system. This means that map orientation with respect to WGS84 North is the sum of the orientation field and any orientation included in a dynamic portion of the reference location. Both values default to zero if no value is specified.
This type uses a single-precision floating-point value of degrees relative to North.
In XML, the <orientation> element contains a single floating-point value, for example, <orientation>67.00</orientation>. In TLV form, map orientation uses the code 130:
The optional map scale describes the relationship between the units of measure used in the map, relative to the meters unit used in the relative coordinate system.
This type uses a sequence of IEEE 754 [IEEE.754] single-precision floating-point values to represent scale as a sequence of numeric values. The units of these values are dependent on the type of map and could, for example, be pixels per meter for an image.
A scaling factor is provided for each axis in the coordinate system. For a two-dimensional coordinate system, two values are included to allow for different scaling along the x and y axes independently. For a three-dimensional coordinate system, three values are specified for the x, y, and z axes. Decoders can determine the number of scaling factors by examining the length field.
Alternatively, a single scaling value MAY be used to apply the same scaling factor to all coordinate components.
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Images that use a rows/columns coordinate system often use a left- handed coordinate system. A negative value for the y/rows axis scaling value can be used to account for any change in direction between the y axis used in the relative coordinate system and the rows axis of the image coordinate system.
In XML, the <scale> element MAY contain a single scale value or MAY contain 2 (or 3) values in XML list form. In TLV form, scale uses a type code of 131. The length of the TLV determines how many scale values are present:
Note: The pattern value for "mimeType" has been folded onto multiple lines. Whitespace has been added to conform to comply with document formatting restrictions. Extra whitespace around the line endings MUST be removed before using this schema.
<xs:annotation> <xs:appinfo source="urn:ietf:params:xml:schema:pidf:geopriv10:relative"> Relative Location for PIDF-LO </xs:appinfo> <xs:documentation source="http://ietf.org/rfc/rfc7035.txt"> This schema defines a location representation that allows for the description of locations that are relative to another. An optional map reference is also defined. </xs:documentation> </xs:annotation>
This document describes a data format. To a large extent, security properties of this depend on how this data is used.
Privacy for location data is typically important. Adding relative location may increase the precision of the location but does not otherwise alter its privacy considerations, which are discussed in [RFC4119].
The map URL provided in a relative location could accidentally reveal information if a Location Recipient uses the URL to acquire the map. The coverage area of a map, or parameters of the URL itself, could provide information about the location of a Target. In combination with other information that could reveal the set of potential Targets that the Location Recipient has location information for, acquiring a map could leak significant information. In particular, it is important to note that the Target and Location Recipient are often the same entity.
Access to map URLs MUST be secured with TLS [RFC5246] (that is, restricting the map URL to be an https URI), unless the map URL cannot leak information about the Target's location. This restricts information about the map URL to the entity serving the map request. If the map URL conveys more information about a Target than a map server is authorized to receive, that URL MUST NOT be included in the PIDF-LO.
This document creates a new registry called "Relative Location Parameters". This shares a page, titled "Civic Address Types Registry" with the existing "Civic Address Types (CAtypes)" registry. As defined in [RFC5226], this new registry operates under "IETF Review" rules.
The content of this registry includes:
Relative Location Code (RLtype): Numeric identifier, assigned by IANA.
Brief description: Short description identifying the meaning of the element.
Reference to published specification: A stable reference to an RFC that describes the value in sufficient detail so that interoperability between independent implementations is possible.
Values requested to be assigned into this registry MUST NOT conflict with values assigned in the "Civic Address Types (CAtypes)" registry or vice versa, unless the IANA Considerations section for the new value explicitly overrides this prohibition and the document defining the value describes how conflicting TLV codes will be interpreted by implementations. To ensure this, the CAtypes entries are explicitly reserved in the initial values table below. Those reserved entries can be changed, but only with caution, as explained here.
To make this clear for future users of the registry, the following note is added to the "Civic Address Types (CAtypes)" registry:
The registration of new values should be accompanied by a corresponding reservation in the Relative Location Parameters registry.
Similarly, the "Relative Location Parameters" registry bears the note:
The registration of new values should be accompanied by a corresponding reservation in the Civic Address Types (CAtypes) registry.
This section registers two URNs for use in identifying relative coordinate reference systems. These are added to a new "Geopriv Identifiers" registry according to the procedures in Section 4 of [RFC3553]. The "Geopriv Identifiers" registry is entered under the "Uniform Resource Name (URN) Namespace for IETF Use" category.
Registrations in this registry follow the "IETF Review" [RFC5226] policy.
Index value: Values in this registry are URNs or URN prefixes that start with the prefix "urn:ietf:params:geopriv:". Each is registered independently.
Each registration in the "Geopriv Identifiers" registry requires the following information:
URN: The complete URN that is used or the prefix for that URN.
Description: A summary description for the URN or URN prefix.
Specification: A reference to a specification describing the URN or URN prefix.
Contact: Email for the person or groups making the registration.
Index value: As described in [RFC3553], URN prefixes that are registered include a description of how the URN is constructed. This is not applicable for specific URNs.
The "Geopriv Identifiers" registry has two initial registrations, included in the following sections.
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8.4.1. Registration of Two-Dimensional Relative Coordinate Reference System URN
This section registers the "urn:ietf:params:geopriv:relative:2d" URN in the "Geopriv Identifiers" registry.
URN: urn:ietf:params:geopriv:relative:2d
Description: A two-dimensional relative coordinate reference system
This document is the product of a design team on relative location. Besides the authors, this team included Marc Linsner, James Polk, and James Winterbottom.
[Clinger1990] Clinger, W., "How to Read Floating Point Numbers Accurately", Proceedings of Conference on Programming Language Design and Implementation, pp. 92-101, 1990.
[IEEE.754] IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE Standard 754-2008, August 2008.
[OGC.GML-3.1.1] Cox, S., Daisey, P., Lake, R., Portele, C., and A. Whiteside, "Geographic information - Geography Markup Language (GML)", OpenGIS 03-105r1, April 2004, <http://portal.opengeospatial.org/files/ ?artifact_id=4700>.
[OGC.GeoShape] Thomson, M. and C. Reed, "GML 3.1.1 PIDF-LO Shape Application Schema for use by the Internet Engineering Task Force (IETF)", OGC Best Practice 06-142r1, Version: 1.0, April 2007.
[RFC1014] Sun Microsystems, Inc., "XDR: External Data Representation standard", RFC 1014, June 1987.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An IETF URN Sub-namespace for Registered Protocol Parameters", BCP 73, RFC 3553, June 2003.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004.
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[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005.
[RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration Information", RFC 4776, November 2006.
[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location Format for Presence Information Data Format Location Object (PIDF-LO)", RFC 5139, February 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[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.
[RFC5962] Schulzrinne, H., Singh, V., Tschofenig, H., and M. Thomson, "Dynamic Extensions to the Presence Information Data Format Location Object (PIDF-LO)", RFC 5962, September 2010.
[RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, "Dynamic Host Configuration Protocol Options for Coordinate-Based Location Configuration Information", RFC 6225, July 2011.
[RFC6848] Winterbottom, J., Thomson, M., Barnes, R., Rosen, B., and R. George, "Specifying Civic Address Extensions in the Presence Information Data Format Location Object (PIDF- LO)", RFC 6848, January 2013.
[WGS84] US National Imagery and Mapping Agency, "Department of Defense (DoD) World Geodetic System 1984 (WGS 84), Third Edition", NIMA TR8350.2, January 2000.
[RFC3863] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004.
[RFC4479] Rosenberg, J., "A Data Model for Presence", RFC 4479, July 2006.
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Authors' Addresses
Martin Thomson Microsoft 3210 Porter Drive Palo Alto, CA 94304 US
