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Versions: (draft-winterbottom-geopriv-pdif-lo-profile) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 5491

Geopriv                                                  J. Winterbottom
Internet-Draft                                                M. Thomson
Expires: September 6, 2007                            Andrew Corporation
                                                           H. Tschofenig
                                           Siemens Networks GmbH & Co KG
                                                           March 5, 2007


GEOPRIV PIDF-LO Usage Clarification, Considerations and Recommendations
               draft-ietf-geopriv-pdif-lo-profile-06.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).












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Abstract

   The Presence Information Data Format Location Object (PIDF-LO)
   specification provides a flexible and versatile means to represent
   location information.  There are, however, circumstances that arise
   when information needs to be constrained in how it is represented so
   that the number of options that need to be implemented in order to
   make use of it are reduced.  There is growing interest in being able
   to use location information contained in a PIDF-LO for routing
   applications.  To allow successfully interoperability between
   applications, location information needs to be normative and more
   tightly constrained than is currently specified in the PIDF-LO.  This
   document makes recommendations on how to constrain, represent and
   interpret locations in a PIDF-LO.  It further recommends a subset of
   GML that MUST be implemented by applications involved in location
   based routing.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Using Location Information . . . . . . . . . . . . . . . . . .  6
     3.1.  Single Civic Location Information  . . . . . . . . . . . .  8
     3.2.  Civic and Geospatial Location Information  . . . . . . . .  8
     3.3.  Manual/Automatic Configuration of Location Information . .  9
   4.  Geodetic Coordinate Representation . . . . . . . . . . . . . . 10
   5.  Geodetic Shape Representation  . . . . . . . . . . . . . . . . 11
     5.1.  Polygon Restrictions . . . . . . . . . . . . . . . . . . . 12
     5.2.  Complex Shape Examples . . . . . . . . . . . . . . . . . . 12
       5.2.1.  Polygon Representation and Usage . . . . . . . . . . . 12
       5.2.2.  Prism Representation and Usage . . . . . . . . . . . . 14
       5.2.3.  Arc Band Respresentation and Usage . . . . . . . . . . 16
       5.2.4.  Ellipsoid Representation and Usage . . . . . . . . . . 18
     5.3.  Emergency Shape Representations  . . . . . . . . . . . . . 20
   6.  Recommendations  . . . . . . . . . . . . . . . . . . . . . . . 22
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 25
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     10.1. Normative references . . . . . . . . . . . . . . . . . . . 26
     10.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
   Intellectual Property and Copyright Statements . . . . . . . . . . 28

























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1.  Introduction

   The Presence Information Data Format Location Object (PIDF-LO) [2] is
   the IETF recommended way of encoding location information and
   associated privacy policies.  Location information in a PIDF-LO may
   be described in a geospatial manner based on a subset of GMLv3, or as
   civic location information [4].  A GML profile for expressing
   geodetic shapes in a PIDF-LO is described in [6].  Uses for PIDF-LO
   are envisioned in the context of numerous location based
   applications.  This document makes recommendations for formats and
   conventions to make interoperability less problematic.








































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2.  Terminology

   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 [1].

   The definition for "Target" is taken from [5].

   In this document a "discrete location" is defined as a place, point,
   area or volume in which a Target can be found.  It must be described
   with sufficient precision to address the requirements of an intended
   application.

   The term "location complex" is used to describe location information
   represented by a composite of both civic and geodetic information.
   An example of a location complex might be a geodetic polygon
   describing the perimeter of a building and a civic element
   representing the floor in the building.

































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3.  Using Location Information

   The PIDF format provides for an unbounded number of tuples.  The
   geopriv element resides inside the status component of a tuple, hence
   a single PIDF document may contain an arbitrary number of location
   objects some or all of which may be contradictory or complementary.
   The actual location information is contained inside a <location-info>
   element, and there may be one or more actual locations described
   inside the <location-info> element.

   Graphically, the structure of the PIDF-LO can be depicted as follows:


   PIDF document
      tuple 1
          status
               geopriv
                   location-info
                       civicAddress
                       geodetic
                       location...
                   usage-rules
               geopriv 2
               geopriv 3
               .
               .
               .

      tuple 2
      tuple 3



   All of these potential sources and storage places for location lead
   to confusion for the generators, conveyors and users of location
   information.  Practical experience within the United States National
   Emergency Number Association (NENA) in trying to solve these
   ambiguities led to a set of conventions being adopted.  These rules
   do not have any particular order, but should be followed by creators
   and users of location information contained in a PIDF-LO to ensure
   that a consistent interpretation of the data can be achieved.

   Rule #1:  A geopriv element MUST describe a discrete location.








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   Rule #2:  Where a discrete location can be uniquely described in more
      than one way, each location description SHOULD reside in a
      separate tuple.


   Rule #3:  Providing more than one location in a single presence
      document (PIDF) MUST only be done if all objects describe the same
      location.  This may occur if a Target's location is determined
      using a series of different techniques.


   Rule #4:  Providing more than one location in a single <location-
      info> element SHOULD be avoided where possible.


   Rule #5:  When providing more than one location in a single
      <location-info> element the locations MUST be provided by a common
      source at the same time and by the same method.


   Rule #6:  Providing more than one location in a single <location-
      info> element SHOULD only be done if they form a complex to
      describe the same location.  For example, a geodetic location
      describing a point, and a civic location indicating the floor in a
      building.


   Rule #7:  Where a location complex is provided in a single <location-
      info> element, the coarse location information MUST be provided
      first.  For example, a geodetic location describing an area, and a
      civic location indicating the floor should be represented with the
      area first followed by the civic location.


   Rule #8:  Where a PIDF document contains more than one tuple
      containing a status element with a geopriv location element , the
      priority of tuples SHOULD be based on tuple position within the
      PIDF document.  That is to say, the tuple with the highest
      priority location occurs earliest in the PIDF document.


   Rule #9:  Where multiple PIDF documents can be sent or received
      together, say in a multi-part MIME body, and current location
      information is required by the recipient, then document selection
      SHOULD be based on document order, with the first document be
      considered first.

   The following examples illustrate the application of these rules.



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3.1.  Single Civic Location Information

   Jane is at a coffee shop on the ground floor of a large shopping
   mall.  Jane turns on her laptop and connects to the coffee-shop's
   WiFi hotspot, Jane obtains a complete civic address for her current
   location, for example using the DHCP civic mechanism defined in [3].
   A Location Object is constructed consisting of a single PIDF
   document, with a single geopriv tuple, and a single location residing
   in the <location-info> element.  This document is unambiguous, and
   should be interpreted consistently by receiving nodes if sent over
   the network.

3.2.  Civic and Geospatial Location Information

   Mike is visiting his Seattle office and connects his laptop into the
   Ethernet port in a spare cube.  In this case the location is a
   geodetic location, with the altitude represented as a building floor
   number.  Mike's main location is the point specified by the geodetic
   coordinates.  Further, Mike is on the second floor of the building
   located at these coordinates.  Applying rules #6 and #7 are applied,
   the PIDF-LO document creates a complex as shown below.


   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:pidf"
      xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
      xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
      xmlns:gml="http://www.opengis.net/gml"
      entity="pres:mike@seattle.example.com">
     <tuple id="sg89ab">
       <status>
         <gp:geopriv>
           <gp:location-info>
             <gml:Point srsName="urn:ogc:def:crs:EPSG::4326"
                <gml:pos>-43.5723 153.21760</gml:pos>
             </gml:Point>
             <cl:civicAddress>
               <cl:FLR>2</cl:FLR>
             </cl:civicAddress>
           </gp:location-info>
           <gp:usage-rules/>
         </gp:geopriv>
       </status>
       <timestamp>2003-06-22T20:57:29Z</timestamp>
     </tuple>
   </presence>





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3.3.  Manual/Automatic Configuration of Location Information

   Loraine has a predefined civic location stored in her laptop, since
   she normally lives in Sydney, the address is for her Sydney-based
   apartment.  Loraine decides to visit sunny San Francisco, and when
   she gets there she plugs in her laptop and makes a call.  Loraine's
   laptop receives a new location from the visited network in San
   Francisco.  As this system cannot be sure that the pre-existing, and
   new location, describe the same place, Loraine's computer generates a
   new PIDF-LO and will use this to represent Loraine's location.  If
   Loraine's computer were to add the new location to her existing PIDF
   location document (breaking rule #3), then the correct information
   may still be interpreted by location recipient providing Loraine's
   system applies rule #9.  In this case the resulting order of location
   information in the PIDF document should be San Francisco first,
   followed by Sydney.  Since the information is provided by different
   sources, rule #8 should also be applied and the information placed in
   different tuples with the tuple containing the San Francisco location
   first.
































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4.  Geodetic Coordinate Representation

   The geodetic examples provided in RFC 4119 [2] are illustrated using
   the gml:location element which uses the gml:coordinates elements
   (inside the gml:Point element) and this representation has several
   drawbacks.  Firstly, it has been deprecated in later versions of GML
   (3.1 and beyond) making it inadvisable to use for new applications.
   Secondly, the format of the coordinates type is opaque and so can be
   difficult to parse and interpret to ensure consistent results, as the
   same geodetic location can be expressed in a variety of ways.  The
   PIDF-LO Geodetic Shapes specification [6] provides a specific GML
   profile for expressing commonly used shapes using simple GML
   representations.  The shapes defined in [6] are the recommended
   shapes to ensure interoperability between location based
   applications.




































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5.  Geodetic Shape Representation

   The cellular mobile world today makes extensive use of geodetic based
   location information for emergency and other location-based
   applications.  Generally these locations are expressed as a point
   (either in two or three dimensions) and an area or volume of
   uncertainty around the point.  In theory, the area or volume
   represents a coverage in which the user has a relatively high
   probability of being found, and the point is a convenient means of
   defining the centroid for the area or volume.  In practice, most
   systems use the point as an absolute value and ignore the
   uncertainty.  It is difficult to determine if systems have been
   implemented in this manner for simplicity, and even more difficult to
   predict if uncertainty will play a more important role in the future.
   An important decision is whether an uncertainty area should be
   specified.

   The PIDF-LO Geodetic Shapes specification [6] defines eight shape
   types most of which are easily translated into shapes definitions
   used in other applications and protocols, such as Open Mobile
   Alliance (OMA) Mobile Location Protocol (MLP).  For completeness the
   shapes defined in [6] are listed below:

   o  Point (2d or 3d)

   o  Polygon (2d)

   o  Circle (2d)

   o  Ellipse (2d)

   o  Arc band (2d)

   o  Sphere (3d)

   o  Ellipsoid (3d)

   o  Prism (3d)

   The GeoShape specification [6] also describes a standard set of
   coordinate reference systems (CRS), unit of measure (UoM) and
   conventions relating to lines and distances.  GeoShape mandates the
   use the WGS-84 Coordinate reference system and restricts usage to
   EPSG-4326 for two dimensional (2d) shape representations and EPSG-
   4979 for three dimensional (3d) volume representations.  Distance and
   heights are expressed in meters using EPSG-9001.

   It is RECOMMENDED that where uncertainty is included, a confidence of



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   68% (or one standard deviation) is used.  Specifying a convention for
   confidence enables better use of uncertainty values.

5.1.  Polygon Restrictions

   The Polygon shape type defined in [6] intentionally does not place
   any constraints on the number of vertices that may be included to
   define the bounds of the Polygon.  This allows arbitrarily complex
   shapes to be defined and conveyed in a PIDF-LO.  However where
   location information is to be used in real-time processing
   applications, such as location dependent routing, having arbitrarily
   complex shapes consisting of tens or even hundreds of points could
   result in significant performance impacts.  To mitigate this risk it
   is recommended that Polygons be restricted to a maximum of 15
   discrete points (16 including the repeated point) when the location
   information is intended for use in real-time applications.  This
   limit of 15 points is chosen to allow moderately complex shape
   definitions while at the same time enabling interoperation with other
   location transporting protocols such as those defined in 3GPP ([7])
   and OMA where the 15 point limit is already imposed.

   Polygons are defined with the minimum distance between two adjacent
   vertices (geodesic).  A connecting line SHALL NOT cross another
   connecting line of the same Polygon.  Polygons SHOULD be defined with
   the upward normal pointing up, this is accomplished by defining the
   vertices in counter-clockwise direction.

   Points specified in a polygon must be coplanar, and it is recommended
   that where points are specified in 3 dimensions that all points
   maintain the same altitude.

5.2.  Complex Shape Examples

   This section provides some examples of where some of the more complex
   shapes are used, how they are determined, and how they are
   represented in a PIDF-LO.  Complete details on all of the Geoshape
   types are provided in [6].

5.2.1.  Polygon Representation and Usage

   The polygon shape may be used to represent a building outline or
   coverage area.  The first and last points of the polygon must be the
   same to form a closed shape.  For example looking at the octagon
   below with vertices, A,H,G,F,E,D,C,B,A. The resulting polygon will be
   defined with 9 points, with the first and last points both having the
   coordinates of point A.





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        B-------------C
      /                \
     /                  \
    /                    \
   A                      D
   |                      |
   |                      |
   |                      |
   |                      |
   H                      E
    \                    /
     \                  /
      \                /
       G--------------F





































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   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:pidf"
    xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
    xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
    xmlns:gs="http://www.opengis.net/pidflo/1.0"
    xmlns:gml="http://www.opengis.net/gml"
      entity="pres:octagon@example.com">
     <tuple id="sg89ab">
       <status>
         <gp:geopriv>
           <gp:location-info>
             <gml:Polygon srsName="urn:ogc:def:crs:EPSG::4326">
               <gml:exterior>
                 <gml:LinearRing>
                   <gml:pos>43.311 -73.422</gml:pos> <!--A-->
                   <gml:pos>43.211 -73.422</gml:pos> <!--H-->
                   <gml:pos>43.111 -73.322</gml:pos> <!--G-->
                   <gml:pos>43.111 -73.222</gml:pos> <!--F-->
                   <gml:pos>43.211 -73.122</gml:pos> <!--E-->
                   <gml:pos>43.311 -73.122</gml:pos> <!--D-->
                   <gml:pos>43.411 -73.222</gml:pos> <!--C-->
                   <gml:pos>43.411 -73.322</gml:pos> <!--B-->
                   <gml:pos>43.311 -73.422</gml:pos> <!--A-->
                 </gml:LinearRing>
              </gml:exterior>
             </gml:Polygon>
           </gp:location-info>
           <gp:usage-rules/>
         </gp:geopriv>
       </status>
       <timestamp>2007-06-22T20:57:29Z</timestamp>
     </tuple>
   </presence>


5.2.2.  Prism Representation and Usage

   A prsim may be used to represent a section of a building or range of
   floors of building.  The prism extrudes a polygon by providing a
   height element.  It consists of a base made up of coplanar 3 points
   defined in 3 dimensions all at the same altitude.  The prism is then
   an extrusion from this base to the value specified in the height
   element.  If the height is negative, then the prism is extruded from
   the top down, while a positive height extrudes from the bottom up.
   The first and last points of the polygon must be the same to form a
   closed shape.

   For example looking at the cube below.  If the prism is extruded from



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   the bottom up, then the polygon forming the base of the prism is
   defined with the points A, B, C, D, A. The height of the prism is the
   distance between point A and point E in meters.  The resulting
   PIDF-LO is provided below.


              G-----F
             /|    /|
            / |   / |
           H--+--E  |
           |  C--|--B
           | /   | /
           |/    |/
           D-----A





































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   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:pidf"
    xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
    xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
    xmlns:gs="http://www.opengis.net/pidflo/1.0"
    xmlns:gml="http://www.opengis.net/gml"
      entity="pres:mike@someprism.example.com">
     <tuple id="sg89ab">
       <status>
         <gp:geopriv>
           <gp:location-info>
             <gs:Prism srsName="urn:ogc:def:crs:EPSG::4979">
               <gs:base>
                  <gml:Polygon>
                     <gml:exterior>
                       <gml:LinearRing>
                          <gml:posList>
                              42.556844 -73.248157 36.6 <!--A-->
                              42.656844 -73.248157 36.6 <!--B-->
                              42.656844 -73.348157 36.6 <!--C-->
                              42.556844 -73.348157 36.6 <!--D-->
                              42.556844 -73.248157 36.6 <!--A-->
                           </gml:posList>
                        </gml:LinearRing>
                     </gml:exterior>
                  </gml:Polygon>
               </gs:base>
               <gs:height uom="urn:ogc:def:uom:EPSG::9001">
                  2.4
               </gs:height>
            </gs:Prism>
           </gp:location-info>
           <gp:usage-rules/>
         </gp:geopriv>
       </status>
       <timestamp>2007-06-22T20:57:29Z</timestamp>
     </tuple>
   </presence>


5.2.3.  Arc Band Respresentation and Usage

   The arc band shape type is commonly generated in wireless systems
   where timing advance or code offsets sequences are used to compensate
   for distances between handsets and the access point.  The arc band is
   represented as two radii emanating from a central point, and two
   angles which represent the starting angle and the opening angle of
   the arc.  In a cellular environment the central point is nominally



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   the location of the cell tower, the two radii are determined by the
   extent of the timing advance, and the two angles are generally
   provisioned information.

   For example, Paul is using a cellular wireless device and is 7 timing
   advance symbols away from the cell tower.  For a GSM-based network
   this would place Paul roughly between 3,594 meters and 4,148 meters
   from the cell tower, providing the inner and outer radius values.  If
   the start angle is 20 degrees from north, and the opening angle is
   120 degrees, an arc band representing Paul's location would look
   similar to the figure below.


         N ^        ,.__
           | a(s)  /     `-.
           | 20   /         `-.
           |--.  /             `.
           |   `/                \
           |   /__                \
           |  .   `-.              \
           | .       `.             \
           |. \        \             .
        ---c-- a(o) -- |             | -->
           |.  / 120   '             |   E
           |  .       /              '
           |    .    /              ;
                  .,'              /
               r(i)`.             /
            (3594m)  `.          /
                       `.      ,'
                         `.  ,'
                       r(o)`'
                     (4148m)


   The resulting PIDF-LO is reflected below.















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   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:pidf"
    xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
    xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
    xmlns:gs="http://www.opengis.net/pidflo/1.0"
    xmlns:gml="http://www.opengis.net/gml"
      entity="pres:paul@somecell.example.com">
     <tuple id="sg89ab">
       <status>
         <gp:geopriv>
           <gp:location-info>
             <gs:ArcBand srsName="urn:ogc:def:crs:EPSG::4326">
                <gml:pos>
                  -43.5723 153.21760
                </gml:pos>
                <gs:innerRadius uom="urn:ogc:def:uom:EPSG::9001">
                  3594
                </gs:innerRadius>
                <gs:outerRadius uom="urn:ogc:def:uom:EPSG::9001">
                  4148
                </gs:outerRadius>
                <gs:startAngle uom="urn:ogc:def:uom:EPSG::9102">
                  20
                </gs:startAngle>
                <gs:openingAngle uom="urn:ogc:def:uom:EPSG::9102">
                  20
                </gs:openingAngle>
             </gs:ArcBand>
           </gp:location-info>
           <gp:usage-rules/>
         </gp:geopriv>
       </status>
       <timestamp>2003-06-22T20:57:29Z</timestamp>
     </tuple>
   </presence>


   An important note to make on the arc band is that the center point
   used in the definition of the shape is not included in resulting
   enclosed area, and that Target may be anywhere in the defined area of
   the arc band.

5.2.4.  Ellipsoid Representation and Usage

   The ellipsoid is the volume most commonly produced by GPS systems.
   It is used extensively in navigation systems and wireless location
   networks.  The ellipsoid is constructed around a central point
   specified in three dimensions, and three axies perpendicular to one



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   another are extended outwards from this point.  These axies are
   defined as the semi-major (M) axis, the semi-minor (m) axis, and the
   vertical (v) axis respectively.  An angle is used to express the
   orientation of the ellipsoid.  The orientation angle is measured in
   degrees from north, and represents the direction of the semi-major
   axis from the center point.


                  \
                _.-\""""^"""""-._
              .'    \   |        `.
             /       v  m          \
            |         \ |           |
            |          -c ----M---->|
            |                       |
             \                     /
              `._               _.'
                 `-...........-'


   A PIDF-LO containing an ellipsoid would like something like the
   sample below.





























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   <?xml version="1.0" encoding="UTF-8"?>
   <presence xmlns="urn:ietf:params:xml:ns:pidf"
    xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
    xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
    xmlns:gs="http://www.opengis.net/pidflo/1.0"
    xmlns:gml="http://www.opengis.net/gml"
      entity="pres:somone@gpsreceiver.example.com">
     <tuple id="sg89ab">
       <status>
         <gp:geopriv>
           <gp:location-info>
             <gs:Ellipsoid srsName="urn:ogc:def:crs:EPSG::4979">
               <gml:pos>
                 42.5463 -73.2512 26.3
               </gml:pos>
               <gs:semiMajorAxis uom="urn:ogc:def:uom:EPSG::9001">
                 7.7156
               </gs:semiMajorAxis>
               <gs:semiMinorAxis uom="urn:ogc:def:uom:EPSG::9001">
                 3.31
               </gs:semiMinorAxis>
              <gs:verticalAxis uom="urn:ogc:def:uom:EPSG::9001">
                28.7
              </gs:verticalAxis>
              <gs:orientation uom="urn:ogc:def:uom:EPSG::9102">
                90
              </gs:orientation>
             </gs:Ellipsoid>
           </gp:location-info>
           <gp:usage-rules/>
         </gp:geopriv>
       </status>
       <timestamp>2003-06-22T20:57:29Z</timestamp>
     </tuple>
   </presence>


5.3.  Emergency Shape Representations

   In some parts of the world cellular networks constraints are placed
   on the shape types that can be used to represent the location of an
   emergency caller.  These restrictions, while to some extend are
   artificial, may pose significant interoperability problems in
   emergency networks were they to be unilaterally lifted.  The largest
   impact likely being on Public Safety Answer Point (PSAP) where
   multiple communication networks report emergency data.  Wholesale
   swap-out or upgrading of this equipment is deemed to be complex and
   costly and has resulted in a number of countries, most notably the



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   United States, to adopt migratory standards towards emergency IP
   telephony support.  Where these migratory standards are implemented
   restrictions on acceptable geodetic shape types to represent the
   location of an emergency caller may exist.  Conversion from one shape
   type to another should be avoided to eliminate the introduction of
   errors in reported location.

   In North America the migratory VoIP emergency services standard (i2)
   [8] reuses the NENA E2 interface [9] which restriction geodetic shape
   representation to a point, a point with an uncertain circle, a point
   with an altitude and an uncertainty circle.  The NENA recommended
   shapes can be represented in a PIDF-LO using the GeoShape Point,
   GeoShape Circle, and GeoShape Sphere definitions respectively.






































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6.  Recommendations

   As a summary, this document gives a few recommendations on the usage
   of location information in PIDF-LO.  Nine rules specified in
   Section 3 give guidelines on avoiding ambiguity in PIDF-LO
   interpretations when multiple locations may be provided to a Target
   or location recipient.

   It is recommended that only the shape types and shape representations
   described in [6] be used to express geodetic locations for exchange
   between general applications.  By standardizing geodetic data
   representation interoperability issues are mitigated.

   It is recommended that GML Polygons be restricted to a maximum of 16
   points when used in location-dependent routing and other real-time
   applications to mitigate possible performance issues.  This allows
   for interoperability with other location protocols where this
   restriction applies.

   Geodetic location may require restricted shape definitions in regions
   where migratory emergency IP telephony implementations are deployed.
   Where the acceptable shape types are not understood restrictions to
   Point, Circle and Sphere representations should be used to
   accommodate most existing deployments.

   Conversions from one geodetic shape type to another should be avoided
   where data is considered critical and the introduction of errors
   considered unacceptable.

   In the absence of any application specific knowledge shapes and
   volumes should assumed to have a corresponding confidence value of
   68% when associated representing a Target's location.



















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7.  Security Considerations

   The primary security considerations relate to how location
   information is conveyed and used, which are outside the scope of this
   document.  This document is intended to serve only as a set of
   guidelines as to which elements MUST or SHOULD be implemented by
   systems wishing to perform location dependent routing.  The
   ramification of such recommendations is that they extend to devices
   and clients that wish to make use of such services.










































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8.  IANA Considerations

   This document does not introduce any IANA considerations.
















































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9.  Acknowledgments

   The authors would like to thank the GEOPRIV working group for their
   discussions in the context of PIDF-LO, in particular Carl Reed, Ron
   Lake, James Polk and Henning Schulzrinne.  Furthermore, we would like
   to thank Jon Peterson as the author of PIDF-LO and Nadine Abbott for
   her constructive comments in clarifying some aspects of the document.












































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10.  References

10.1.  Normative references

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", March 1997.

   [2]   Peterson, J., "A Presence-based GEOPRIV Location Object
         Format", RFC 4119, December 2005.

   [3]   Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
         and DHCPv6) Option for Civic Addresses Configuration
         Information", RFC 4676, October 2006.

   [4]   Thomson, M. and J. Winterbottom, "Revised Civic Location Format
         for PIDF-LO", draft-ietf-geopriv-revised-civic-lo-05 (work in
         progress), February 2007.

   [5]   Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
         Polk, "Geopriv Requirements", RFC 3693, February 2004.

   [6]   Thomson, M. and C. Reed, "GML 3.1.1 PIDF-LO Shape Application
         Schema for use by the Internet Engineering Task Force (IETF)",
         Candidate OpenGIS Implementation Specification 06-142, Version:
         0.0.9, December 2006.

10.2.  Informative References

   [7]   "3GPP TS 23.032 V6.0.0 3rd Generation Partnership Project;
         Technical Specification Group Code Network; Universal
         Geographic Area Description (GAD)".

   [8]   "abbrev"i2">NENA VoIP-Packet Technical Committee, Interim VoIP
         Architecture for Enhanced 9-1-1 Services (i2), NENA 08-001, Dec
         2005".

   [9]   "NENA Standard for the Implementation of the Wireless Emergency
         Service Protocol E2 Interface, NENA 05-001, Dec 2003".

   [10]  Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
         Configuration Protocol Option for Coordinate-based Location
         Configuration Information", RFC 3825, July 2004.









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Authors' Addresses

   James Winterbottom
   Andrew Corporation
   Wollongong
   NSW Australia

   Email: james.winterbottom@andrew.com


   Martin Thomson
   Andrew Corporation
   Wollongong
   NSW Australia

   Email: martin.thomson@andrew.com


   Hannes Tschofenig
   Siemens Networks GmbH & Co KG
   Otto-Hahn-Ring 6
   Munich, Bavaria  81739
   Germany

   Email: Hannes.Tschofenig@siemens.com


























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Full Copyright Statement

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