One document matched: draft-ietf-geopriv-pdif-lo-profile-07.txt
Differences from draft-ietf-geopriv-pdif-lo-profile-06.txt
Geopriv J. Winterbottom
Internet-Draft M. Thomson
Updates: 4119 (if approved) Andrew Corporation
Intended status: Standards Track H. Tschofenig
Expires: October 30, 2007 Nokia Siemens Networks
April 28, 2007
GEOPRIV PIDF-LO Usage Clarification, Considerations and Recommendations
draft-ietf-geopriv-pdif-lo-profile-07.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 30, 2007.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Winterbottom, et al. Expires October 30, 2007 [Page 1]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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 RFC 4119
(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 is mandatory to implemented by
applications involved in location based routing.
Winterbottom, et al. Expires October 30, 2007 [Page 2]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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. Shape Examples . . . . . . . . . . . . . . . . . . . . . . 13
5.2.1. Point . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2.2. Polygon . . . . . . . . . . . . . . . . . . . . . . . 14
5.2.3. Circle . . . . . . . . . . . . . . . . . . . . . . . . 15
5.2.4. Ellipse . . . . . . . . . . . . . . . . . . . . . . . 16
5.2.5. Arc Band . . . . . . . . . . . . . . . . . . . . . . . 18
5.2.6. Sphere . . . . . . . . . . . . . . . . . . . . . . . . 19
5.2.7. Ellipsoid . . . . . . . . . . . . . . . . . . . . . . 20
5.2.8. Prism . . . . . . . . . . . . . . . . . . . . . . . . 22
6. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.1. Normative references . . . . . . . . . . . . . . . . . . . 29
10.2. Informative References . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . . . 31
Winterbottom, et al. Expires October 30, 2007 [Page 3]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
1. Introduction
The Presence Information Data Format Location Object (PIDF-LO) [2] is
the 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 [5]. A GML profile for expressing geodetic
shapes in a PIDF-LO is described in [3]. 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.
Winterbottom, et al. Expires October 30, 2007 [Page 4]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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 [6].
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 "compound location" is used to describe location information
represented by a composite of both civic and geodetic information.
An example of compound location might be a geodetic polygon
describing the perimeter of a building and a civic element
representing the floor in the building.
Winterbottom, et al. Expires October 30, 2007 [Page 5]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
3. Using Location Information
The PIDF format provides for an unbounded number of <tuple> elements.
Each <tuple> element contains a single <status> element that may
contain more than one <geopriv> element as a child element. Each
<geopriv> element must contain at least the following two child
elements: <location-info> element and <usage-rules> element. One or
more chunks of location information are contained inside a <location-
info> element.
Hence, a single PIDF document may contain an arbitrary number of
location objects some or all of which may be contradictory or
complementary. Graphically, the structure of a PIDF-LO document can
be depicted as shown in Figure 1.
<?xml version="1.0" encoding="UTF-8"?>
<presence>
<tuple> -- #1
<status>
<geopriv> -- #1
<location-info>
location chunk #1
location chunk #2
...
location chunk #n
<usage-rules>
</geopriv>
<geopriv> -- #2
<geopriv> -- #3
...
<geopriv> -- #m
</status>
</tuple>
<tuple> -- #2
<tuple> -- #3
...
<tuple> -- #o
</presence>
Figure 1: Structure of a PIDF-LO Document
All of these potential sources and storage places for location lead
to confusion for the generators, conveyors and consumers 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
Winterbottom, et al. Expires October 30, 2007 [Page 6]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
do not have any particular order, but should be followed by creators
and consumers 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.
Rule #2: Where a discrete location can be uniquely described in more
than one way, each location description SHOULD reside in a
separate <tuple> element.
Rule #3: Providing more than one location chunk in a single presence
document (PIDF) MUST only be done if all objects refer to the same
place.
This may occur if a Target's location is determined using a
series of different techniques.
Rule #4: Providing more than one location chunk in a single
<location-info> element SHOULD be avoided where possible. Rule #5
and Rule #6 provide further refinement.
Rule #5: When providing more than one location chunk in a single
<location-info> element the locations MUST be provided by a common
source at the same time and by the same location determination
method.
Rule #6: Providing more than one location chunk in a single
<location-info> element SHOULD only be used for representing
compound location referring to the same place.
For example, a geodetic location describing a point, and a
civic location indicating the floor in a building.
Rule #7: Where compound location 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.
Winterbottom, et al. Expires October 30, 2007 [Page 7]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
Rule #8: Where a PIDF document contains more than one <tuple>
element containing a <status> element with a <geopriv> element,
the priority of tuples SHOULD be based on position of the <tuple>
element 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.
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 [4].
A Location Object is constructed consisting of a single PIDF
document, with a single <tuple> element, a single <status> element, a
single <geopriv> element, and a single location chunk 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 location information is
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 resulting compound location information is shown below.
Winterbottom, et al. Expires October 30, 2007 [Page 8]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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>
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 the 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.
Winterbottom, et al. Expires October 30, 2007 [Page 9]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
4. Geodetic Coordinate Representation
The geodetic examples provided in RFC 4119 [2] are illustrated using
the <gml:location> element, which uses the <gml:coordinates> element
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 [3] provides a specific GML
profile for expressing commonly used shapes using simple GML
representations. The shapes defined in [3] are the recommended
shapes to ensure interoperability.
Winterbottom, et al. Expires October 30, 2007 [Page 10]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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 [3] 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 [3] are listed below:
o Point (2d and 3d)
o Polygon (2d)
o Circle (2d)
o Ellipse (2d)
o Arc band (2d)
o Sphere (3d)
o Ellipsoid (3d)
o Prism (3d)
All above-listed shapes are mandatory to implement.
The GeoShape specification [3] also describes a standard set of
coordinate reference systems (CRS), unit of measure (UoM) and
conventions relating to lines and distances. The use of the WGS-84
coordinate reference system and the usage of EPSG-4326 (as identified
by the URN urn:ogc:def:crs:EPSG::4326) for two dimensional (2d) shape
representations and EPSG-4979 (as identified by the URN
urn:ogc:def:crs:EPSG::4979) for three dimensional (3d) volume
Winterbottom, et al. Expires October 30, 2007 [Page 11]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
representations is mandated. Distance and heights are expressed in
meters using EPSG-9001 (as identified by the URN
urn:ogc:def:uom:EPSG::9001). Angular measures MUST use either
degrees or radians. Measures in degrees MUST be identified by the
URN urn:ogc:def:uom:EPSG::9102, measures in radians MUST be
identified by the URN urn:ogc:def:uom:EPSG::9101
Implementations MUST specify the CRS using the srsName attribute on
the outermost geometry element. The CRS MUST NOT be respecified or
changed for any sub-elements. The srsDimension attribute SHOULD be
omitted, since the number of dimensions in these CRSs is known. A
CRS MUST be specified using the above URN notation only,
implementations do not need to support user-defined CRSs.
It is RECOMMENDED that where uncertainty is included, a confidence of
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 [3] intentionally does not place
any constraints on the number of vertices that may be included to
define the bounds of a 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 Polygon shapes be restricted to a maximum of 15
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 (see
[8]) 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.
Winterbottom, et al. Expires October 30, 2007 [Page 12]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
5.2. 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 [3].
5.2.1. Point
The point shape type is the simplest form of geodetic LI, which is
natively supported by GML. The gml:Point element is used when there
is no known uncertainty. A point also forms part of a number of
other geometries. A point may be specified using either WGS 84
(latitude, longitude) or WGS 84 (latitude, longitude, altitude). The
next example shows a 2d point:
<?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:point2d@example.com">
<tuple id="sg89abcd">
<status>
<gp:geopriv>
<gp:location-info>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326"
xmlns:gml="http://www.opengis.net/gml">
<gml:pos>-34.407 150.883</gml:pos>
</gml:Point>
</gp:location-info>
<gp:usage-rules/>
</gp:geopriv>
</status>
<timestamp>2007-06-22T20:57:29Z</timestamp>
</tuple>
</presence>
The next example shows a 3d point:
Winterbottom, et al. Expires October 30, 2007 [Page 13]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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:point3d@example.com">
<tuple id="sg89ab5">
<status>
<gp:geopriv>
<gp:location-info>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4979"
xmlns:gml="http://www.opengis.net/gml">
<gml:pos>-34.407 150.883 24.8</gml:pos>
</gml:Point>
</gp:location-info>
<gp:usage-rules/>
</gp:geopriv>
</status>
<timestamp>2007-06-22T20:57:29Z</timestamp>
</tuple>
</presence>
5.2.2. Polygon
The polygon shape may be used to represent a building outline or
coverage area. The first and last points of the polygon have to be
the same. 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.
B-------------C
/ \
/ \
/ \
A D
| |
| |
| |
| |
H E
\ /
\ /
\ /
G--------------F
Winterbottom, et al. Expires October 30, 2007 [Page 14]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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>
5.2.3. Circle
The circular area is used for coordinates in two-dimensional CRSs to
describe uncertainty about a point. The definition is based on the
one-dimensional geometry in GML, gml:CircleByCenterPoint. The centre
point of a circular area is specified by using a two dimensional CRS;
in three dimensions, the orientation of the circle cannot be
specified correctly using this representation. A point with
uncertainty that is specified in three dimensions should use the
Sphere shape type.
Winterbottom, et al. Expires October 30, 2007 [Page 15]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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:circle@example.com">
<tuple id="sg89ab1">
<status>
<gp:geopriv>
<gp:location-info>
<gs:Circle srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>
42.5463 -73.2512
</gml:pos>
<gml:radius uom="urn:ogc:def:uom:EPSG::9001">
850.24
</gml:radius>
</gs:Circle>
</gp:location-info>
</gp:geopriv>
</status>
</tuple>
</presence>
5.2.4. Ellipse
An elliptical area describes an ellipse in two dimensional space.
The ellipse is described by a center point, the length of its semi-
major and semi-minor axes, and the orientation of the semi-major
axis. Like the circular area (Circle), the ellipse MUST be specified
using a two dimensional CRS.
Winterbottom, et al. Expires October 30, 2007 [Page 16]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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:Ellipse@somecell.example.com">
<tuple id="sg89ab7">
<status>
<gp:geopriv>
<gp:location-info>
<gs:Ellipse srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>
42.5463 -73.2512
</gml:pos>
<gs:semiMajorAxis uom="urn:ogc:def:uom:EPSG::9001">
1275
</gs:semiMajorAxis>
<gs:semiMinorAxis uom="urn:ogc:def:uom:EPSG::9001">
670
</gs:semiMinorAxis>
<gs:orientation uom="urn:ogc:def:uom:EPSG::9102">
43.2
</gs:orientation>
</gs:Ellipse>
</gp:location-info>
<gp:usage-rules/>
</gp:geopriv>
</status>
<timestamp>2003-06-22T20:57:29Z</timestamp>
</tuple>
</presence>
The gml:pos element indicates the position of the center, or origin,
of the ellipse. The gs:semiMajorAxis and gs:semiMinorAxis elements
are the length of the semi-major and semi-minor axes respectively.
The gs:orientation element is the angle by which the semi-major axis
is rotated from the first axis of the CRS towards the second axis.
For WGS 84, the orientation indicates rotation from Northing to
Easting, which, if specified in degrees, is roughly equivalent to a
compass bearing (if magnetic north were the same as the WGS north
pole). Note: An ellipse with equal major and minor axis lengths is a
circle.
Winterbottom, et al. Expires October 30, 2007 [Page 17]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
5.2.5. Arc Band
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
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.
Winterbottom, et al. Expires October 30, 2007 [Page 18]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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.
5.2.6. Sphere
The sphere is a volume that provides the same information as a circle
in three dimensions. The sphere has to be specified using a three
dimensional CRS. The following example shows a sphere shape, which
is identical to the circle example, except for the addition of an
Winterbottom, et al. Expires October 30, 2007 [Page 19]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
altitude in the provided coordinates.
<?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:circle@example.com">
<tuple id="sg89ab1">
<status>
<gp:geopriv>
<gp:location-info>
<gs:Sphere srsName="urn:ogc:def:crs:EPSG::4979">
<gml:pos>
42.5463 -73.2512 26.3
</gml:pos>
<gs:radius uom="urn:ogc:def:uom:EPSG::9001">
850.24
</gs:radius>
</gs:Sphere>
</gp:location-info>
</gp:geopriv>
</status>
</tuple>
</presence>
5.2.7. Ellipsoid
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
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.
Winterbottom, et al. Expires October 30, 2007 [Page 20]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
\
_.-\""""^"""""-._
.' \ | `.
/ v m \
| \ | |
| -c ----M---->|
| |
\ /
`._ _.'
`-...........-'
A PIDF-LO containing an ellipsoid would like something like the
sample below.
Winterbottom, et al. Expires October 30, 2007 [Page 21]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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>
5.2.8. Prism
A prism 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 have to be the same.
Winterbottom, et al. Expires October 30, 2007 [Page 22]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
For example, looking at the cube below. If the prism is extruded
from 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
Winterbottom, et al. Expires October 30, 2007 [Page 23]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
<?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>
Winterbottom, et al. Expires October 30, 2007 [Page 24]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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 [3] 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.
Winterbottom, et al. Expires October 30, 2007 [Page 25]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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.
Winterbottom, et al. Expires October 30, 2007 [Page 26]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
8. IANA Considerations
This document does not introduce any IANA considerations.
Winterbottom, et al. Expires October 30, 2007 [Page 27]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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.
Winterbottom, et al. Expires October 30, 2007 [Page 28]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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] 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
[4] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
and DHCPv6) Option for Civic Addresses Configuration
Information", RFC 4776, November 2006.
[5] Thomson, M. and J. Winterbottom, "Revised Civic Location Format
for PIDF-LO", draft-ietf-geopriv-revised-civic-lo-05 (work in
progress), February 2007.
[6] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[7] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004.
[8] "3GPP TS 23.032 V6.0.0 3rd Generation Partnership Project;
Technical Specification Group Code Network; Universal Geographic
Area Description (GAD)".
Winterbottom, et al. Expires October 30, 2007 [Page 29]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
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
Nokia Siemens Networks
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: Hannes.Tschofenig@nsn.com
URI: http://www.tschofenig.com
Winterbottom, et al. Expires October 30, 2007 [Page 30]
Internet-Draft GEOPRIV PIDF-LO Profile April 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Winterbottom, et al. Expires October 30, 2007 [Page 31]
| PAFTECH AB 2003-2026 | 2026-04-22 07:47:37 |