draft-ietf-geopriv-pdif-lo-profile-04.txt   draft-ietf-geopriv-pdif-lo-profile-05.txt 
Geopriv J. Winterbottom Geopriv J. Winterbottom
Internet-Draft M. Thomson Internet-Draft M. Thomson
Expires: November 3, 2006 Andrew Corporation Intended status: Informational Andrew Corporation
H. Tschofenig Expires: April 26, 2007 H. Tschofenig
Siemens Siemens
May 2, 2006 October 23, 2006
GEOPRIV PIDF-LO Usage Clarification, Considerations and Recommendations GEOPRIV PIDF-LO Usage Clarification, Considerations and Recommendations
draft-ietf-geopriv-pdif-lo-profile-04.txt draft-ietf-geopriv-pdif-lo-profile-05.txt
Status of this Memo Status of this Memo
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skipping to change at page 1, line 36 skipping to change at page 1, line 36
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This Internet-Draft will expire on November 3, 2006. This Internet-Draft will expire on April 26, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
The Presence Information Data Format Location Object (PIDF-LO) The Presence Information Data Format Location Object (PIDF-LO)
specification provides a flexible and versatile means to represent specification provides a flexible and versatile means to represent
location information. There are, however, circumstances that arise location information. There are, however, circumstances that arise
skipping to change at page 2, line 15 skipping to change at page 3, line 7
applications. To allow successfully interoperability between applications. To allow successfully interoperability between
applications, location information needs to be normative and more applications, location information needs to be normative and more
tightly constrained than is currently specified in the PIDF-LO. This tightly constrained than is currently specified in the PIDF-LO. This
document makes recommendations on how to constrain, represent and document makes recommendations on how to constrain, represent and
interpret locations in a PIDF-LO. It further recommends a subset of interpret locations in a PIDF-LO. It further recommends a subset of
GML that MUST be implemented by applications involved in location GML that MUST be implemented by applications involved in location
based routing. based routing.
Table of Contents Table of Contents
1. CHANGES SINCE LAST TIME . . . . . . . . . . . . . . . . . . . 3 1. CHANGES SINCE LAST TIME . . . . . . . . . . . . . . . . . . . 4
1.1. 04 changes . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. 05 changes . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. 03 changes . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. 04 changes . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. 01 changes . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. 03 changes . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4. 01 changes . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. To Do . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Using Location Information . . . . . . . . . . . . . . . . . . 7 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Single Civic Location Information . . . . . . . . . . . . 8 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Civic and Geospatial Location Information . . . . . . . . 9 5. Using Location Information . . . . . . . . . . . . . . . . . . 9
4.3. Manual/Automatic Configuration of Location Information . . 12 5.1. Single Civic Location Information . . . . . . . . . . . . 11
5. Geodetic Coordinate Representation . . . . . . . . . . . . . . 13 5.2. Civic and Geospatial Location Information . . . . . . . . 11
6. Geodetic Shape Representation . . . . . . . . . . . . . . . . 14 5.3. Manual/Automatic Configuration of Location Information . . 12
6.1. Polygon Restriction . . . . . . . . . . . . . . . . . . . 15 6. Geodetic Coordinate Representation . . . . . . . . . . . . . . 14
6.2. Emergency Shape Representations . . . . . . . . . . . . . 15 7. Geodetic Shape Representation . . . . . . . . . . . . . . . . 15
7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 16 7.1. Polygon Restriction . . . . . . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 7.2. Emergency Shape Representations . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 8. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative references . . . . . . . . . . . . . . . . . . . 20 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . . 20 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Uncertainty in The RFC-3825 LCI Representation . . . 21 12.1. Normative references . . . . . . . . . . . . . . . . . . . 21
A.1. Conversion From LCI Form . . . . . . . . . . . . . . . . . 21 12.2. Informative References . . . . . . . . . . . . . . . . . . 21
Appendix A. Uncertainty in The RFC-3825 LCI Representation . . . 22
A.1. Conversion From LCI Form . . . . . . . . . . . . . . . . . 22
A.2. Conversion To LCI Form . . . . . . . . . . . . . . . . . . 22 A.2. Conversion To LCI Form . . . . . . . . . . . . . . . . . . 22
A.2.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . 22 A.2.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . 23
A.2.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . 23 A.2.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . 24
A.3. Problem . . . . . . . . . . . . . . . . . . . . . . . . . 23 A.3. Problem . . . . . . . . . . . . . . . . . . . . . . . . . 24
A.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 23 A.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 24
Appendix B. Creating a PIDF-LO from DHCP Geo Encoded Data . . . . 25 Appendix B. Creating a PIDF-LO from DHCP Geo Encoded Data . . . . 26
B.1. Latitude and Longitude . . . . . . . . . . . . . . . . . . 25 B.1. Latitude and Longitude . . . . . . . . . . . . . . . . . . 26
B.2. Altitude . . . . . . . . . . . . . . . . . . . . . . . . . 27 B.2. Altitude . . . . . . . . . . . . . . . . . . . . . . . . . 28
B.3. Generating the PIDF-LO . . . . . . . . . . . . . . . . . . 27 B.3. Generating the PIDF-LO . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33
Intellectual Property and Copyright Statements . . . . . . . . . . 33 Intellectual Property and Copyright Statements . . . . . . . . . . 34
1. CHANGES SINCE LAST TIME 1. CHANGES SINCE LAST TIME
[[This section is informational only and will be removed before the [[This section is informational only and will be removed before the
final version.]] final version.]]
1.1. 04 changes 1.1. 05 changes
Clarified definitions more.
Clarified rules.
Clarified examples, and removed confusion caused by the illustration
of how not to represent location.
1.2. 04 changes
Added a section to recommend restricting Polygon to 16 points for Added a section to recommend restricting Polygon to 16 points for
routing and other real-time applications. routing and other real-time applications.
Added section detailing caution when selecting shapes for emergency Added section detailing caution when selecting shapes for emergency
routing. routing.
Modified the recommendations section to include the two above Modified the recommendations section to include the two above
additions. additions.
Added a second appendix detailing problems with expressing Added a second appendix detailing problems with expressing
uncertainty using LCI. uncertainty using LCI.
1.2. 03 changes 1.3. 03 changes
Removed some shape definitions, ellipses, arcbands. Removed some shape definitions, ellipses, arcbands.
Removed OMA shape definition comparisons. Removed OMA shape definition comparisons.
Modified examples to use new civicAddr draft data. Modified examples to use new civicAddr draft data.
Made extensive references to the GeoShape Draft. Made extensive references to the GeoShape Draft.
1.3. 01 changes 1.4. 01 changes
minor changes to the abstract. minor changes to the abstract.
Minor changes to the introduction. Minor changes to the introduction.
Added and appendix to take implementers through how to create a Added and appendix to take implementers through how to create a
PIDF-LO from data received using DHCP option 123 as defined in [3]. PIDF-LO from data received using DHCP option 123 as defined in [3].
Rectified examples to use position and pos rather than location and Rectified examples to use position and pos rather than location and
point. point.
skipping to change at page 5, line 5 skipping to change at page 6, line 5
Corrected example 3 so that it does not violate SIP rules. Corrected example 3 so that it does not violate SIP rules.
Added addition geopriv elements to the status component of the figure Added addition geopriv elements to the status component of the figure
in "Using Location Information" to more accurately reflect the in "Using Location Information" to more accurately reflect the
cardinality issues. cardinality issues.
Revised text in section Geodetic Coordinate Representation. Removed Revised text in section Geodetic Coordinate Representation. Removed
last example as this was addressed with the change to position and last example as this was addressed with the change to position and
pos in previous examples. pos in previous examples.
2. Introduction 2. To Do
Get Appendices moved into the RFC 3825 Biz document.
Get an OGC reference for the GeoShapes specification
3. Introduction
The Presence Information Data Format Location Object (PIDF-LO) [2] is The Presence Information Data Format Location Object (PIDF-LO) [2] is
the IETF recommended way of encoding location information and the IETF recommended way of encoding location information and
associated privacy policies. Location information in a PIDF-LO may associated privacy policies. Location information in a PIDF-LO may
be described in a geospatial manner based on a subset of GMLv3, or as be described in a geospatial manner based on a subset of GMLv3, or as
civic location information [5]. A GML profile for expressing civic location information [5]. A GML profile for expressing
geodetic shapes in a PIDF-LO is described in [6].Uses for PIDF-LO are geodetic shapes in a PIDF-LO is described in [7]. Uses for PIDF-LO
envisioned in the context of numerous location based applications. are envisioned in the context of numerous location based
This document makes recommendations for formats and conventions to applications. This document makes recommendations for formats and
make interoperability less problematic. conventions to make interoperability less problematic.
3. Terminology 4. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [1]. document are to be interpreted as described in [1].
In this document a "discrete location" is defined as a location that The definition for "Target" is taken from [6].
can be found based on the information used to describe it. It is not
necessarily a single point in space, but may be an area or volume
depending on what is being defined and the required precision.
4. Using Location Information 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.
5. Using Location Information
The PIDF format provides for an unbounded number of tuples. The The PIDF format provides for an unbounded number of tuples. The
geopriv element resides inside the status component of a tuple, hence geopriv element resides inside the status component of a tuple, hence
a single PIDF document may contain an arbitrary number of location a single PIDF document may contain an arbitrary number of location
objects some or all of which may be contradictory or complementary. objects some or all of which may be contradictory or complementary.
The actual location information is contained inside a <location-info> The actual location information is contained inside a <location-info>
element, and there may be one or more actual locations described element, and there may be one or more actual locations described
inside the <location-info> element. inside the <location-info> element.
Graphically, the structure of the PIDF/PIDF-LO can be depicted as Graphically, the structure of the PIDF/PIDF-LO can be depicted as
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. .
. .
tuple 2 tuple 2
tuple 3 tuple 3
All of these potential sources and storage places for location lead All of these potential sources and storage places for location lead
to confusion for the generators, conveyors and users of location to confusion for the generators, conveyors and users of location
information. Practical experience within the United States National information. Practical experience within the United States National
Emergency Number Association (NENA) in trying to solve these Emergency Number Association (NENA) in trying to solve these
ambiguities led the following conventions being adopted: 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 conatined 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 #1: A geopriv element MUST describe a discrete location.
Rule #2: Where a discrete location can be uniquely described in more Rule #2: Where a discrete location can be uniquely described in more
than one way, each location description SHOULD reside in a than one way, each location description SHOULD reside in a
separate tuple. separate tuple.
Rule #3: Providing more than one location in a single presence Rule #3: Providing more than one location in a single presence
document (PIDF) MUST only be done if all objects describe the same document (PIDF) MUST only be done if all objects describe the same
location. 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> Rule #4: Providing more than one location in a single <location-
element SHOULD be avoided where possible. info> element SHOULD be avoided where possible.
Rule #5: When providing more than one location in a single <location- Rule #5: When providing more than one location in a single
info> element the locations MUST be provided by a common source. <location-info> element the locations MUST be provided by a common
source.
Rule #6: Providing more than one location in a single <location-info> Rule #6: Providing more than one location in a single <location-
element SHOULD only be done if they form a complex to describe the info> element SHOULD only be done if they form a complex to
same location. For example, a geodetic location describing a describe the same location. For example, a geodetic location
point, and a civic location indicating the floor in a building. 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- Rule #7: Where a location complex is provided in a single <location-
info> element, the macro locations MUST be provided first. For info> element, the coarse location information MUST be provided
example, a geodetic location describing an area, and a civic first. For example, a geodetic location describing an area, and a
location indicating the floor MUST be represented with the area civic location indicating the floor should be represented with the
first followed by the civic location. area first followed by the civic location.
Rule #8: Where a PIDF document contains more than one tuple Rule #8: Where a PIDF document contains more than one tuple
containing a status element with a geopriv location element , the containing a status element with a geopriv location element , the
priority of tuples SHOULD be based on tuple position within the priority of tuples SHOULD be based on tuple position within the
PIDF document. That is to say, the tuple with the highest PIDF document. That is to say, the tuple with the highest
priority location occurs earliest in the PIDF document. Initial priority location occurs earliest in the PIDF document.
priority SHOULD be determined by the originating UA, the final
priority MAY be determined by a proxy along the way, or the UAS.
Rule #9: Where multiple PIDF documents are contained within a single Rule #9: Where multiple PIDF documents can be sent of received
request, document selection SHOULD be based on document order. 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. The following examples illustrate the application of these rules.
4.1. Single Civic Location Information 5.1. Single Civic Location Information
Jane is at a coffee shop on the ground floor of a large shopping 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 mall. Jane turns on her laptop and connects to the coffee-shop's
WiFi hotspot, Jane obtains a complete civic address for her current WiFi hotspot, Jane obtains a complete civic address for her current
location, for example using the DHCP Civic mechanism defined in [4]. location, for example using the DHCP civic mechanism defined in [4].
A Location Object is constructed consisting of a single PIDF A Location Object is constructed consisting of a single PIDF
document, with a single geopriv tuple, and a single location residing document, with a single geopriv tuple, and a single location residing
in the <location-info> element. This document is unambiguous, and in the <location-info> element. This document is unambiguous, and
should be interpreted consitently by receiving nodes if sent over the should be interpreted consitently by receiving nodes if sent over the
network. network.
4.2. Civic and Geospatial Location Information 5.2. Civic and Geospatial Location Information
Mike is visiting his Seattle office and connects his laptop into the Mike is visiting his Seattle office and connects his laptop into the
Ethernet port in a spare cube. Mike's computer receives a location Ethernet port in a spare cube. In this case the location is a
over DHCP as defined in RFC-3825 [3]. In this case the location is a
geodetic location, with the altitude represented as a building floor geodetic location, with the altitude represented as a building floor
number. This is constructed by Mike's computer into the following number. The main location of user is inside the rectangle bounded by
PIDF document: the geodetic coordinates specified. Further that the user is on the
second floor of the building located at these coordinates. Applying
<?xml version="1.0" encoding="UTF-8"?> rules #6 and #7 are applied, the PIDF-LO document creates a complex
<presence xmlns="urn:ietf:params:xml:ns:pidf" as shown below.
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape"
entity="pres:mike@seattle.example.com">
<tuple id="sg89ab">
<status>
<gp:geopriv>
<gp:location-info>
<cl:civicAddress>
<cl:FLR>2</cl:FLR>
</cl:civicAddress>
</gp:location-info>
<gp:usage-rules/>
</gp:geopriv>
</status>
<timestamp>2006-01-30T20:57:29Z</timestamp>
</tuple>
<tuple id="sg89ae">
<status>
<gp:geopriv>
<gp:location-info>
<Polygon srsName="urn:ogc:def::crs:EPSG::4326"
xmlns="http://www.opengis.net/gml">
<exterior>
<LinearRing>
<pos>37.775 -122.4194</pos>
<pos>37.555 -122.4194</pos>
<pos>37.555 -122.4264</pos>
<pos>37.775 -122.4264</pos>
<pos>37.775 -122.4194</pos>
</LinearRing>
</exterior>
</Polygon>
</gp:location-info>
<gp:usage-rules/>
</gp:geopriv>
</status>
<timestamp>2006-01-30T20:57:29Z</timestamp>
</tuple>
</presence>
The constructed PIDF document contains two geopriv elements each in a
separate PIDF tuple, the first being a civic address made up of only
floor, the second containing the provided geodetic information. If
the location is required for routing purposes, which information is
used? Applying rule #8, we will likely fail, or at a minimum need to
fall back to the second tuple describing the geodetic location, a
route described by floor only is not precise enough in the normal
case to permit route selection. If rule #6 and #7 are applied, then
the revised PIDF-LO document creates a complex as shown below.
<?xml version="1.0" encoding="UTF-8"?> <?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf" <presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10" xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr" xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape" xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape"
entity="pres:mike@seattle.example.com"> entity="pres:mike@seattle.example.com">
<tuple id="sg89ab"> <tuple id="sg89ab">
<status> <status>
<gp:geopriv> <gp:geopriv>
skipping to change at page 11, line 43 skipping to change at page 12, line 38
<cl:FLR>2</cl:FLR> <cl:FLR>2</cl:FLR>
</cl:civicAddress> </cl:civicAddress>
</gp:location-info> </gp:location-info>
<gp:usage-rules/> <gp:usage-rules/>
</gp:geopriv> </gp:geopriv>
</status> </status>
<timestamp>2003-06-22T20:57:29Z</timestamp> <timestamp>2003-06-22T20:57:29Z</timestamp>
</tuple> </tuple>
</presence> </presence>
It is now clear that the main location of user is inside the 5.3. Manual/Automatic Configuration of Location Information
rectangle bounded by the geodetic coordinates specified. Further
that the user is on the second floor of the building located at these
coordinates.
4.3. Manual/Automatic Configuration of Location Information
Loraine has a predefined civic location stored in her laptop, since Loraine has a predefined civic location stored in her laptop, since
she normally lives in Sydney, the address in her address is for her she normally lives in Sydney, the address is her address is for her
Sydney-based apartment. Loraine decides to visit sunny San Sydney-based apartment. Loraine decides to visit sunny San
Francisco, and when she gets there she plugs in her laptop and makes 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 a call. Loraine's laptop receives a new location from the visited
network in San Francisco. As this system cannot be sure that the network in San Francisco. As this system cannot be sure that the
pre-existing and new location describe the same place, Loraine's pre-existing and new location describe the same place, Loraine's
computer generates a new PIDF-LO and will use this to represent computer generates a new PIDF-LO and will use this to represent
Loraine's location. If Loraine's computer were to add the new Loraine's location. If Loraine's computer were to add the new
location to her existing PIDF location document (breaking rule #3), location to her existing PIDF location document (breaking rule #3),
then the correct information may still be interpreted by location then the correct information may still be interpreted by location
recipient providing Loraine's system applies rule #9. In this case recipient providing Loraine's system applies rule #9. In this case
the resulting order of location information in the PIDF document the resulting order of location information in the PIDF document
should be San Francisco first, followed by Sydney. Since the should be San Francisco first, followed by Sydney. Since the
information is provided by different sources, rule #8 should also be information is provided by different sources, rule #8 should also be
applied and the information placed in different tuples with San applied and the information placed in different tuples with San
Francisco first. Francisco first.
5. Geodetic Coordinate Representation 6. Geodetic Coordinate Representation
The geodetic examples provided in RFC-4119 [2] are illustrated using The geodetic examples provided in RFC 4119 [2] are illustrated using
the gml:location element which uses the gml:coordinates elements the gml:location element which uses the gml:coordinates elements
(inside the gml:Point element) and this representation has several (inside the gml:Point element) and this representation has several
drawbacks. Firstly, it has been deprecated in later versions of GML drawbacks. Firstly, it has been deprecated in later versions of GML
(3.1 and beyond) making it inadvisable to use for new applications. (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 Secondly, the format of the coordinates type is opaque and so can be
difficult to parse and interpret to ensure consistent results, as the difficult to parse and interpret to ensure consistent results, as the
same geodetic location can be expressed in a variety of ways. The same geodetic location can be expressed in a variety of ways. The
PIDF-LO Geodetic Shapes specification [6] provides a specific GML PIDF-LO Geodetic Shapes specification [7] provides a specific GML
profile for expressing commonly used shapes using simple GML profile for expressing commonly used shapes using simple GML
representations. The shapes defined in [6] are the recommended representations. The shapes defined in [7] are the recommended
shapes to ensure interoperability between location based shapes to ensure interoperability between location based
applications. applications.
6. Geodetic Shape Representation 7. Geodetic Shape Representation
The cellular mobile world today makes extensive use of geodetic based The cellular mobile world today makes extensive use of geodetic based
location information for emergency and other location-based location information for emergency and other location-based
applications. Generally these locations are expressed as a point applications. Generally these locations are expressed as a point
(either in two or three dimensions) and an area or volume of (either in two or three dimensions) and an area or volume of
uncertainty around the point. In theory, the area or volume uncertainty around the point. In theory, the area or volume
represents a coverage in which the user has a relatively high represents a coverage in which the user has a relatively high
probability of being found, and the point is a convenient means of probability of being found, and the point is a convenient means of
defining the centroid for the area or volume. In practice, most defining the centroid for the area or volume. In practice, most
systems use the point as an absolute value and ignore the systems use the point as an absolute value and ignore the
uncertainty. It is difficult to determine if systems have been uncertainty. It is difficult to determine if systems have been
implement in this manner for simplicity, and even more difficult to implement in this manner for simplicity, and even more difficult to
predict if uncertainty will play a more important role in the future. predict if uncertainty will play a more important role in the future.
An important decision is whether an uncertainty area should be An important decision is whether an uncertainty area should be
specified. specified.
The PIDF-LO Geodetic Shapes specification [6] defines eight shape The PIDF-LO Geodetic Shapes specification [7] defines eight shape
types most of which are easily translated in shapes definitions used types most of which are easily translated in shapes definitions used
in other applications and protocol, such as Open Mobile Alliance in other applications and protocol, such as Open Mobile Alliance
(OMA) Mobile Location Protocol (MLP). For completeness the shape (OMA) Mobile Location Protocol (MLP). For completeness the shape
defined in [6] are listed below: defined in [7] are listed below:
o Point (2d or 3d) o Point (2d or 3d)
o Polygon (2d) o Polygon (2d)
o Circle (2d) o Circle (2d)
o Ellipse (2d) o Ellipse (2d)
o Arc band (2d) o Arc band (2d)
o Sphere (3d circle) o Sphere (3d circle)
o Ellipsoid (3d) o Ellipsoid (3d)
o Prism (3d polygon) o Prism (3d polygon)
The GeoShape specification [6] also describes a standard set of The GeoShape specification [7] also describes a standard set of
coordinate reference systems (CRS), unit of measure and conventions coordinate reference systems (CRS), unit of measure and conventions
relating to lines and distances. GeoShape mandates the use the relating to lines and distances. GeoShape mandates the use the
WGS-84 Coordinate reference system and restricts usage to EPSG-4326 WGS-84 Coordinate reference system and restricts usage to EPSG-4326
for two dimensional (2d) shape representations and EPSG-4979 for for two dimensional (2d) shape representations and EPSG-4979 for
three dimensional (3d) volume representations. Distance and heights three dimensional (3d) volume representations. Distance and heights
are expressed in metres using EPSG-9001. are expressed in meters using EPSG-9001.
6.1. Polygon Restriction 7.1. Polygon Restriction
The Polygon shape type defined in [6] intentionally does not place The Polygon shape type defined in [7] intentionally does not place
any constraints on the number of points that may be included to any constraints on the number of vertices that may be included to
define the bounds of the Polygon. This allows arbitrarily complex define the bounds of the Polygon. This allows arbitrarily complex
shapes to be defined and conveyed in a PIDF-LO. However where shapes to be defined and conveyed in a PIDF-LO. However where
location information is to be used in real-time processing location information is to be used in real-time processing
applications, such as location dependent routing, having arbitrarily applications, such as location dependent routing, having arbitrarily
complex shapes consisting of tens or even hundreds of points may complex shapes consisting of tens or even hundreds of points may
result in significant performance impacts. To mitigate this risk it result in significant performance impacts. To mitigate this risk it
is recommended that Polygons be restricted to a maximum of 16 points is recommended that Polygons be restricted to a maximum of 16 points
when the location information is intended for use in real-time when the location information is intended for use in real-time
applications. This limit of 16 points is chosen to allow moderately applications. This limit of 16 points is chosen to allow moderately
complex shape definitions while at the same time enabling complex shape definitions while at the same time enabling
interworking with other location transporting protocols such as those interworking with other location transporting protocols such as those
defined in 3GPP ([7]) and OMA where the 16 point limit is already defined in 3GPP ([8]) and OMA where the 16 point limit is already
imposed. imposed.
6.2. Emergency Shape Representations 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.
7.2. Emergency Shape Representations
In some parts of the world cellular networks constraints are placed 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 on the shape types that can be used to represent the location of an
emergency caller. These restrictions, while to some extend are emergency caller. These restrictions, while to some extend are
artificial, may pose significant interoperability problems in artificial, may pose significant interoperability problems in
emergency networks were they to be unilaterally lifted. The largest emergency networks were they to be unilaterally lifted. The largest
impact likely being on PSAP CPE where multiple communication networks impact likely being on Public Safety Answer Point (PSAP) where
report emergency data. Wholesale swap-out or upgrading of this multiple communication networks report emergency data. Wholesale
equipment is deemed to be complex and costly and has resulted in a swap-out or upgrading of this equipment is deemed to be complex and
number of countries, most notably the United States, to adopt costly and has resulted in a number of countries, most notably the
migratory standards towards emergency IP telephony support. Where United States, to adopt migratory standards towards emergency IP
these migratory standards are implemented restrictions on acceptable telephony support. Where these migratory standards are implemented
geodetic shape types to represent the location of an emergency caller restrictions on acceptable geodetic shape types to represent the
may exist and MUST be adhered to. Conversion from one shape type to location of an emergency caller may exist. Conversion from one shape
another should be avoided to eliminate the introduction of errors in type to another should be avoided to eliminate the introduction of
reported location. errors in reported location.
In North America the migratory VoIP emergency services standard (i2) In North America the migratory VoIP emergency services standard (i2)
implicitly imposes the restriction ([10]) that the geodetic shape be [11] reuses the NENA E2 interface [12] which restriction geodetic
constrained to a point, point and uncertain circle, point with shape representation to a point, a point with an uncertain circle, a
altitude and uncertainty circle. These shapes can be easily point with an altitude and an uncertainty circle. The NENA
represented using the GeoShape specification and map to Point, Circle recommended shapes can be represented in a PIDF-LO using the GeoShape
and Sphere respectively. Point, GeoShape Circle, and GeoShape Sphere definitions respectively.
7. Recommendations 8. Recommendations
As a summary this document gives a few recommendations on the usage As a summary, this document gives a few recommendations on the usage
of location information in PIDF-LO. Nine rules specified in of location information in PIDF-LO. Nine rules specified in
Section 4 give guidelines on the ambiguity of PIDF-LO with regard to Section 5 give guidelines on avoiding ambiguity in PIDF-LO
the occurrence of multiple locations. interpretations when multiple locations may be provided to a Target
or location recipient.
It is recommend that only the shape types and shape representations It is recommend that only the shape types and shape representations
described in [6] be used to express geodetic locations for exchange described in [7] be used to express geodetic locations for exchange
between general applications. By standardizing geodetic data between general applications. By standardizing geodetic data
representation interoperability issues are mitigated. representation interoperability issues are mitigated.
It is recommended that Polygons be restricted to a maximum of 16 It is recommended that GML Polygons be restricted to a maximum of 16
points when used in location-dependent routing and other real-time points when used in location-dependent routing and other real-time
applications to mitigate possible performance issues. This allows applications to mitigate possible performance issues. This allows
for interoperability with other location protocols where this for interoperability with other location protocols where this
restriction applies. restriction applies.
Geodetic location may require restricted shape definitions in regions Geodetic location may require restricted shape definitions in regions
where migratory emergency IP telephony implementations are deployed. where migratory emergency IP telephony implementations are deployed.
Where the acceptable shape types are not understood restrictions to Where the acceptable shape types are not understood restrictions to
Point, Circle and Sphere representations should be used to Point, Circle and Sphere representations should be used to
accommodate most existing deployments. accommodate most existing deployments.
Conversions from one geodetic shape type to another should be avoided Conversions from one geodetic shape type to another should be avoided
where data is considered critical and the introduction of errors where data is considered critical and the introduction of errors
considered unacceptable. considered unacceptable.
If Geodetic information is to be provided via DHCP, then a minimum If geodetic information is to be provided via DHCP, then a minimum
resolution of 20 bits SHOULD be specified for both the Latitude and resolution of 20 bits SHOULD be specified for both the Latitude and
Longitude fields to achieve sub 100 metre precision. Where only two Longitude fields to achieve sub 100 meter precision.
dimensional objects are required polygons SHOULD be used to express
the enclosed area. Where 3 dimensions are required a rectangular
prism SHOULD be used.
8. Security Considerations 9. Security Considerations
The primary security considerations relate to how location The primary security considerations relate to how location
information is conveyed and used, which are outside the scope of this information is conveyed and used, which are outside the scope of this
document. This document is intended to serve only as a set of document. This document is intended to serve only as a set of
guidelines as to which elements MUST or SHOULD be implemented by guidelines as to which elements MUST or SHOULD be implemented by
systems wishing to perform location dependent routing. The systems wishing to perform location dependent routing. The
ramification of such recommendations is that they extend to devices ramification of such recommendations is that they extend to devices
and clients that wish to make use of such services. and clients that wish to make use of such services.
9. IANA Considerations 10. IANA Considerations
This document does not introduce any IANA considerations. This document does not introduce any IANA considerations.
10. Acknowledgments 11. Acknowledgments
The authors would like to thank the GEOPRIV working group for their The authors would like to thank the GEOPRIV working group for their
discussions in the context of PIDF-LO, in particular Carl Reed, Ron discussions in the context of PIDF-LO, in particular Carl Reed, Ron
Lake, James Polk and Henning Schulzrinne. Furthermore, we would like Lake, James Polk and Henning Schulzrinne. Furthermore, we would like
to thank Jon Peterson as the author of PIDF-LO and Nadine Abbott for to thank Jon Peterson as the author of PIDF-LO and Nadine Abbott for
her constructive comments in clarifying some aspects of the document. her constructive comments in clarifying some aspects of the document.
11. References 12. References
11.1. Normative references 12.1. Normative references
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", March 1997. Levels", March 1997.
[2] Peterson, J., "A Presence-based GEOPRIV Location Object Format", [2] Peterson, J., "A Presence-based GEOPRIV Location Object Format",
RFC 4119, December 2005. RFC 4119, December 2005.
[3] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host [3] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004. Configuration Information", RFC 3825, July 2004.
[4] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4 [4] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
and DHCPv6) Option for Civic Addresses Configuration and DHCPv6) Option for Civic Addresses Configuration
Information", draft-ietf-geopriv-dhcp-civil-09 (work in Information", draft-ietf-geopriv-dhcp-civil-09 (work in
progress), January 2006. progress), January 2006.
[5] Thomson, M. and J. Winterbottom, "Revised Civic Location Format [5] Thomson, M. and J. Winterbottom, "Revised Civic Location Format
for PIDF-LO", draft-ietf-geopriv-revised-civic-lo-02 (work in for PIDF-LO", draft-ietf-geopriv-revised-civic-lo-04 (work in
progress), April 2006. progress), September 2006.
[6] Thomson, M., "draft-thomson-geopriv-geo-shape, Geodetic Shapes [6] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[7] Thomson, M., "draft-thomson-geopriv-geo-shape, Geodetic Shapes
for the Representation of Uncertainty in PIDF-LO", January 2006. for the Representation of Uncertainty in PIDF-LO", January 2006.
11.2. Informative References 12.2. Informative References
[7] "3GPP TS 23.032 V6.0.0 3rd Generation Partnership Project; [8] "3GPP TS 23.032 V6.0.0 3rd Generation Partnership Project;
Technical Specification Group Code Network; Universal Technical Specification Group Code Network; Universal
Geographic Area Description (GAD)". Geographic Area Description (GAD)".
[8] Schulzrinne, H., "A Document Format for Expressing Privacy [9] Schulzrinne, H., "Common Policy: A Document Format for
Preferences", draft-ietf-geopriv-common-policy-09 (work in Expressing Privacy Preferences",
progress), April 2006. draft-ietf-geopriv-common-policy-11 (work in progress),
August 2006.
[9] "TR-45 J-STD-036-AD-2 Enhanced Wireless 9-1-1 Phase 2". [10] "TR-45 J-STD-036-AD-2 Enhanced Wireless 9-1-1 Phase 2".
[10] "NENA Standard for the Implementation of the Wireless Emergency [11] "abbrev"i2">NENA VoIP-Packet Technical Committee, Interim VoIP
Service Protocol E2 Interface". Architecture for Enhanced 9-1-1 Services (i2), NENA 08-001, Dec
2005".
[12] "NENA Standard for the Implementation of the Wireless Emergency
Service Protocol E2 Interface, NENA 05-001, Dec 2003".
Appendix A. Uncertainty in The RFC-3825 LCI Representation Appendix A. Uncertainty in The RFC-3825 LCI Representation
This Appendix should be regarded as informative only and provides RFC-3825 [3] defines a binary geodetic representation referred to as
Location Configuration Information LCI. The way that LCI represents
uncertainty is through a resolution parameter that indicates how many
binary digits of each axis are significant or accurate. This is
explained in detail in [3] with a series of examples, with a further
example provided in Appendix B of this document. In short LCI
describes a rectangular prism that is aligned along the north-south/
east-west/up-down axes.
This appendix should be regarded as informative only and provides
guidance on aspects concerning the interpretation of uncertainty as guidance on aspects concerning the interpretation of uncertainty as
it applies to the binary geodetic LCI representation defined in RFC- it applies to the binary geodetic LCI representation defined in RFC-
3825 [3]. No recommendation on the use or otherwise of LCI in 3825 [3].
applications is made. However the risks of introducing large errors
into reported location when LCI is used to represent uncertainty are
clearly explained.
RFC-3825 [3] defines a binary geodetic representation referred to as
LCI. The way that LCI represents uncertainty is through a resolution
parameter that indicates how many binary digits of each axis are
significant or accurate. This is explained in detail in [3] with a
series of examples with a further example provided in Appendix B of
this document. In short LCI describes a rectangular prism that is
aligned along the north-south/east-west/up-down axes.
A.1. Conversion From LCI Form A.1. Conversion From LCI Form
From the example in RFC-3825, 38.89868 degrees is encoded into a From the example in RFC 3825, 38.89868 degrees is encoded into a
34bit twos-complement number: 34bit twos-complement number:
000100110.1110011000001111111001000 000100110.1110011000001111111001000
The resolution value for this axis indicates how many of this bits The resolution value for this axis indicates how many of thess bits
are actually significant. A resolution of 18 indicates that the last are actually significant. A resolution of 18 indicates that the last
16 bits of the number could be either 1 or zero: 16 bits of the number could be either 1 or zero:
000100110.111001100xxxxxxxxxxxxxxxx 000100110.111001100xxxxxxxxxxxxxxxx
To determine the uncertainty assume a range from the minimum possible To determine the uncertainty assume a range from the minimum possible
value (all zeros for the last 16 bits) to the maximum (all ones): value (all zeros for the last 16 bits) to the maximum (all ones):
000100110.1110011000000000000000000 to 000100110.1110011000000000000000000 to
000100110.1110011001111111111111111 000100110.1110011001111111111111111
This yields the range in the example to be between 38.8984375 degrees This yields the range in the example to be between 38.8984375 degrees
and 38.9003906 degrees (rounded to 7 decimal places). and 38.9003906 degrees (rounded to 7 decimal places).
A.2. Conversion To LCI Form A.2. Conversion To LCI Form
This involves converting the original shape to a rectangular prism. Converting location information into the LCI format involves
To do this determine the minimum and maximum values for each of the converting the original shape to a rectangular prism. To do this
axes: latitude, longitude and altitude. This results in a slightly determine the minimum and maximum values for each of the axes:
latitude, longitude and altitude. This results in a slightly
increased area, but the overall effect is minimal. increased area, but the overall effect is minimal.
+----------.....----------+ +----------.....----------+
| _d^^^^^^^^^b_ | | _d^^^^^^^^^b_ |
| .d''yyyyyyyyyyy``b. | | .d''yyyyyyyyyyy``b. |
| .p'yyyyyyyyyyyyyyyyy`q. | | .p'yyyyyyyyyyyyyyyyy`q. |
|.d'yyyyyyyyyyyyyyyyyyy`b.| |.d'yyyyyyyyyyyyyyyyyyy`b.|
.d'yyyyyyyyyyyyyyyyyyyyy`b. .d'yyyyyyyyyyyyyyyyyyyyy`b.
::yyyyyyyyyyyyyyyyyyyyyyy:: ::yyyyyyyyyyyyyyyyyyyyyyy::
:: ................... :: :: ................... ::
skipping to change at page 22, line 40 skipping to change at page 23, line 36
points and the Target may reside at anyone of these points with equal points and the Target may reside at anyone of these points with equal
probability. If the area is cropped there is a risk that the probability. If the area is cropped there is a risk that the
Target's position will be one of the discarded points yielding an Target's position will be one of the discarded points yielding an
incorrect result. In general the increases in area are minimal, for incorrect result. In general the increases in area are minimal, for
a circular area, as shown, the increase ratio is 4:pi; a square a circular area, as shown, the increase ratio is 4:pi; a square
building will at most double the size of the area. building will at most double the size of the area.
A.2.1. Example 1 A.2.1. Example 1
Looking at a random example from 32.98004 degrees to 32.98054397 Looking at a random example from 32.98004 degrees to 32.98054397
degrees the approximate distance is 56 metres. Converting each value degrees the approximate distance is 56 meters. Converting each value
into a The 34-bit twos-complement number yields the following: into a 34-bit twos-complement number yields the following:
000100000.1111101011100011111001110 to 000100000.1111101011100011111001110 to
000100000.1111101100000100111011100 000100000.1111101100000100111011100
^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^
To ensure that the encoded value represents the full range from the To ensure that the encoded value represents the full range from the
lowest to highest value, take the common stem as marked this above. lowest to highest value, take the common stem as marked this above.
There are 16 common bits between low and high. To check, convert the There are 16 common bits between low and high. To check, convert the
value back by making the last 18 bits either 0 or 1 as described value back by making the last 18 bits either 0 or 1 as described
earlier. This leads to a range from 32.9765625 degrees to 32.9843745 earlier. This leads to a range from 32.9765625 degrees to 32.9843745
degrees, which is approximately 870 metres a significant increase degrees, which is approximately 870 meters a significant increase
over the original 56 metres. over the original 56 meters.
A.2.2. Example 2 A.2.2. Example 2
Take the range from 31.9999985 degrees to 32.00000274 degrees, which Take the range from 31.9999985 degrees to 32.00000274 degrees, which
is about 0.5 metres in distances ranging around 32 degrees. This is about 0.5 meters in distances ranging around 32 degrees. This
results in the following binary values: results in the following binary values:
000011111.1111111111111111111001110 to 000011111.1111111111111111111001110 to
000100000.0000000000000000001011100 000100000.0000000000000000001011100
^^^ ^^^
Only 3 bits are common to both values which yields an encoded range Only 3 bits are common to both values which yields an encoded range
from 0 to 64 degrees, or a distance of 3,500 kilometres. from 0 to 64 degrees, or a distance of 3,500 kilometers.
A.3. Problem A.3. Problem
The LCI encoding breaks when the uncertainty that is being The LCI encoding breaks when the uncertainty that is being
represented causes a change in a relatively significant binary digit. represented causes a change in a relatively significant binary digit.
This results in an expanded uncertainty, possibly very large, This results in an expanded uncertainty, possibly very large,
depending on which binary digit changes. In many cases the change depending on which binary digit changes. In many cases the change
will be in lower-order digits, which will result in a relatively will be in lower-order digits, which will result in a relatively
small increase in uncertainty, but certain values will yield an small increase in uncertainty, but certain values will yield an
almost useless location see Appendix A.2.2. almost useless location see Appendix A.2.2.
skipping to change at page 24, line 5 skipping to change at page 24, line 48
determination technologies only reduce the probability of large determination technologies only reduce the probability of large
problems occurring, although the nature of the encoding is such that problems occurring, although the nature of the encoding is such that
any uncertainty can be greatly increased. any uncertainty can be greatly increased.
A.4. Conclusion A.4. Conclusion
Uncertainty is a reality of location and important for a number of Uncertainty is a reality of location and important for a number of
applications. LCI's limited form means that adapting existing applications. LCI's limited form means that adapting existing
uncertainty information, for example a circle as in Appendix A.2.2, uncertainty information, for example a circle as in Appendix A.2.2,
results in a small error. The introduction of this small encoding results in a small error. The introduction of this small encoding
error however is insignificant when compared to the error that can be error is, however, insignificant when compared to the error that can
introduced by the way that the resolution parameter is interpreted. be introduced by the way that the resolution parameter is
interpreted.
Appendix B. Creating a PIDF-LO from DHCP Geo Encoded Data Appendix B. Creating a PIDF-LO from DHCP Geo Encoded Data
This appendix is informative only. This appendix is informative only.
RFC-3825 [3] describes a means by which an end-point may learn it RFC 3825 [3] describes a means by which an end point may learn it
location from information encoded into DHCP option 123. The location from information encoded into DHCP option 123. The
following section describes how and end-point can take this following section describes how and end point can take this
information and represent it in a well formed PIDF-LO describing this information and represent it in a well formed PIDF-LO describing this
geodetic location. geodetic location.
The location information described in RFC-3825 consists of a The location information described in RFC 3825 consists of a
latitude, longitude, altitude and datum. latitude, longitude, altitude and datum.
B.1. Latitude and Longitude B.1. Latitude and Longitude
The latitude and longitude values are represented in degrees and The latitude and longitude values are represented in degrees and
decimal degrees. Latitude values are positive if north of the decimal degrees. Latitude values are positive if north of the
equator, and negative if south of the equator. Similarly equator, and negative if south of the equator. Similarly
longitudinal values are positive if east of the Greenwich meridian, longitudinal values are positive if east of the Greenwich meridian,
and negative if west of the Greenwich meridian. and negative if west of the Greenwich meridian.
skipping to change at page 25, line 37 skipping to change at page 26, line 37
consisting of a 9 bit integer component and a 25 bit fraction consisting of a 9 bit integer component and a 25 bit fraction
component, with negative numbers being represented in 2s complement component, with negative numbers being represented in 2s complement
notation. The latitude and longitude fields are each proceeded by a notation. The latitude and longitude fields are each proceeded by a
6 bit resolution field, the LaRes for latitude, and the LoRes for 6 bit resolution field, the LaRes for latitude, and the LoRes for
longitude. The value in the LaRes field indicates the number of longitude. The value in the LaRes field indicates the number of
significant bits to interpret in the Latitude field, while the value significant bits to interpret in the Latitude field, while the value
in the LoRes field indicates the number of significant bits to in the LoRes field indicates the number of significant bits to
interpret in the Longitude field. interpret in the Longitude field.
For example, if you are in Wollongong Australia which is located at For example, if you are in Wollongong Australia which is located at
34 Degrees 25 minutes South and 150 degrees 32 minutes East this 34 Degrees 25 minutes South and 150 degrees 32 minutes East, this
would translate to -34.41667, 150.53333 in decimal degrees. If these would translate to -34.41667, 150.53333 in decimal degrees. If these
numbers are translated to their full 34 bit representations, then we numbers are translated to their full 34 bit representations, then we
arrive the following: arrive the following:
Latitude = 111011101.1001010101010101000111010 Latitude = 111011101.1001010101010101000111010
Longitude = 0100101101000100010001000010100001 Longitude = 0100101101000100010001000010100001
RFC-3825, uses the LaRes and LoRes values to specify a lower and RFC 3825, uses the LaRes and LoRes values to specify a lower and
upper boundary for location thereby specifying an area. The size of upper boundary for location thereby specifying an area. The size of
the area specified is directly related to the value specified in the the area specified is directly related to the value specified in the
LaRes and LoRes fields. LaRes and LoRes fields.
Using the previous example, if LaRes is set 7, then lower latitude Using the previous example, if LaRes is set 7, then lower latitude
boundary can be calculated as -256+128+64+16+8+4, which is -36 boundary can be calculated as -256+128+64+16+8+4, which is -36
degrees, the upper boundary then becomes -256+128+64+16+8+4+2+1 which degrees, the upper boundary then becomes -256+128+64+16+8+4+2+1 which
is -35 degrees. LoRes may be used similarly for Longitude. is -35 degrees. LoRes may be used similarly for Longitude.
So what level of precision is useful? Well, certain types of So what level of precision is useful? Well, certain types of
applications and regulations call for different levels of precision, applications and regulations call for different levels of precision,
and the required precision may vary depending on how the location was and the required precision may vary depending on how the location was
determined. For Cellular 911 calls in the United States, for determined. For cellular 911 calls in the United States, for
example, if the network measures the location then the caller should example, if the network measures the location then the caller should
be within 100 metres, while if the handset does the measurement then be within 100 meters, while if the handset does the measurement then
the location should be within 50 metres. Since DHCP is a network the location should be within 50 meters. Since DHCP is a network
based mechanism we will benchmark off 100 metres (approximately 330 based mechanism we will benchmark off 100 meters (approximately 330
ft) which is still a large area. ft) which is still a large area.
For simplicity we shall assume that we are defining a square, in For simplicity we shall assume that we are defining a square, in
which we are equally to appear anywhere. The greatest distance which we are equally to appear anywhere. The greatest distance
through this square is across the diagonal, so we make this 100 through this square is across the diagonal, so we make this 100
metres. meters.
+----------------------+ +----------------------+
| _/| | _/|
| _/ | | _/ |
| _/ | | _/ |
| _/ | | _/ |
| _/ | | _/ |
| 100_/ metres | | 100_/ metres |
| _/ | | _/ |
| _/ | | _/ |
| _/ | | _/ |
| _/ | | _/ |
|_/ | |_/ |
+----------------------+ +----------------------+
The distance between the top and the bottom and the left and the The distance between the top and the bottom and the left and the
right is the same, the area being a square, and this works out to be right is the same, the area being a square, and this works out to be
70.7 metres. When expressed in decimal degrees, the third point 70.7 meters. When expressed in decimal degrees, the third point
after the decimal place represents about 100 metre precision, this after the decimal place represents about 100 meter precision, this
equates to 10 binary places of fractional part. A 70 metre distance equates to 10 binary places of fractional part. A 70 meter distance
is required, so 11 fractional binary digits are necessary resulting is required, so 11 fractional binary digits are necessary resulting
in a total of 20 bits of precision. in a total of 20 bits of precision.
With -34.4167, 150.5333 encoded with 20 bits of precision for the With -34.4167, 150.5333 encoded with 20 bits of precision for the
LaRes and LoRes, the corners of the enclosing square are: LaRes and LoRes, the corners of the enclosing square are:
Point 1 (-34.4170, 150.5332) Point 1 (-34.4170, 150.5332)
Point 2 (-34.4170, 150.5337) Point 2 (-34.4170, 150.5337)
Point 3 (-34.4165, 150.5332) Point 3 (-34.4165, 150.5332)
Point 4 (-34.4165, 150.5337) Point 4 (-34.4165, 150.5337)
B.2. Altitude B.2. Altitude
The altitude elements define how the altitude is encoded and to what The altitude elements define how the altitude is encoded and to what
level of precision. The units for altitude are either metres, or level of precision. The units for altitude are either meters, or
floors, with the actual measurement being encoded in a similar manner floors, with the actual measurement being encoded in a similar manner
to those for latitude and longitude, but with 22 bit integer, and 8 to those for latitude and longitude, but with 22 bit integer, and 8
bit fractional components. bit fractional components.
B.3. Generating the PIDF-LO B.3. Generating the PIDF-LO
If altitude is not required, or is expressed in floors then a If altitude is not required, or is expressed in floors then a
geodetic location expressed by a polygon SHOULD be used, with points geodetic location expressed by a polygon SHOULD be used, with points
expressed in a counter-clockwise direction. If the altitude is expressed in a counter-clockwise direction. If the altitude is
expressed in floors and is required, the altitude SHOULD be expressed expressed in floors and is required, the altitude SHOULD be expressed
skipping to change at page 27, line 41 skipping to change at page 28, line 41
<LinearRing> <LinearRing>
<pos>-34.4165 150.5332</pos> <pos>-34.4165 150.5332</pos>
<pos>-34.4170 150.5532</pos> <pos>-34.4170 150.5532</pos>
<pos>-34.4170 150.5537</pos> <pos>-34.4170 150.5537</pos>
<pos>-34.4165 150.5337</pos> <pos>-34.4165 150.5337</pos>
<pos>-34.4165 150.5332</pos> <pos>-34.4165 150.5332</pos>
</LinearRing> </LinearRing>
</exterior> </exterior>
</Polygon> </Polygon>
If a floor number of say 3 were included, then the location-;info No Altitude
If a floor number of say 3 were included, then the location-info
element would contain the above information and the following: element would contain the above information and the following:
<civicAddress <civicAddress
xlmns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"> xlmns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr">
<FLR>2</FLR> <FLR>2</FLR>
</civicAddress> </civicAddress>
Civic Altitude
When altitude is expressed as an integer and fractional component, as When altitude is expressed as an integer and fractional component, as
with the latitude and longitude, it expresses a range which requires with the latitude and longitude, it expresses a range which requires
the prism form to be used. Care must be taken to ensure that the the prism form to be used. Care must be taken to ensure that the
points are defined in a counter-clockwise direction to ensure that points are defined in a counter-clockwise direction to ensure that
the upward normal points up. the upward normal points up.
Extending the previous example to include an altitude expressed in Extending the previous example to include an altitude expressed in
metres rather than floors. AltRes is set to a value of 19, and the metres rather than floors. AltRes is set to a value of 19, and the
Altitude value is set to 34. Using similar techniques as shown in Altitude value is set to 34. Using similar techniques as shown in
the latitude and longitude section, a range of altitudes between 32 the latitude and longitude section, a range of altitudes between 32
metres and 40 metres is described. The prism would therefore be meters and 40 meters is described. The prism would therefore be
defined as follows: defined as follows:
<Prism srsName="urn:ogc:def:crs:EPSG::4976" <Prism srsName="urn:ogc:def:crs:EPSG::4976"
xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape" xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape"
xmlns:gml="http://www.opengis.net/gml"> xmlns:gml="http://www.opengis.net/gml">
<base> <base>
<gml:Polygon> <gml:Polygon>
<gml:exterior> <gml:exterior>
<gml:LinearRing> <gml:LinearRing>
<gml:pos>-34.4165 150.5332 32</gml:pos> <gml:pos>-34.4165 150.5332 32</gml:pos>
skipping to change at page 28, line 38 skipping to change at page 29, line 42
<gml:pos>-34.4165 150.5332 32</gml:pos> <gml:pos>-34.4165 150.5332 32</gml:pos>
</gml:LinearRing> </gml:LinearRing>
</gml:exterior> </gml:exterior>
</gml:Polygon> </gml:Polygon>
</base> </base>
<height uom="urn:ogc:def:uom:EPSG::9001"> <height uom="urn:ogc:def:uom:EPSG::9001">
8 8
</height> </height>
</Prism> </Prism>
The Method value SHOULD be set to DHCP. Note that this case, the The Method value SHOULD be set to Wiremap.
DHCP is referring to the way in which location information was
delivered to the IP-device, and not necessarily how the location was
determined.
The timestamp value SHOULD be set to the time that location was The timestamp value SHOULD be set to the time that location was
retrieved from the DHCP server. retrieved from the DHCP server.
The client application MAY insert any usage rules that are pertinent The client application MAY insert any usage rules that are pertinent
to the user of the device and that comply with [8]. A guideline is to the user of the device and that comply with [9]. A guideline is
that the any retention-expiry value SHOULD NOT exceed the current that the any retention-expiry value SHOULD NOT exceed the current
lease time. lease time.
The Provided-By element SHOULD NOT be populated as this is not The Provided-By element SHOULD NOT be populated as this is not
provided by the source of the location information. provided by the source of the location information.
The 3 completed PIDF-LO representations are provided below, and The 3 completed PIDF-LO representations are provided below, and
represent a location without altitude, a location with a civic represent a location without altitude, a location with a civic
altitude, and a location represented as a 3 dimensional rectangular altitude, and a location represented as a 3 dimensional rectangular
prism. prism.
skipping to change at page 29, line 38 skipping to change at page 30, line 40
<gml:pos>-34.4165 150.5332</gml:pos> <gml:pos>-34.4165 150.5332</gml:pos>
<gml:pos>-34.4170 150.5532</gml:pos> <gml:pos>-34.4170 150.5532</gml:pos>
<gml:pos>-34.4170 150.5537</gml:pos> <gml:pos>-34.4170 150.5537</gml:pos>
<gml:pos>-34.4165 150.5337</gml:pos> <gml:pos>-34.4165 150.5337</gml:pos>
<gml:pos>-34.4165 150.5332</gml:pos> <gml:pos>-34.4165 150.5332</gml:pos>
</gml:LinearRing> </gml:LinearRing>
</gml:exterior> </gml:exterior>
</gml:Polygon> </gml:Polygon>
</gp:location-info> </gp:location-info>
<gp:usage-rules/> <gp:usage-rules/>
<gp:method>DHCP</gp:method> <gp:method>Wiremap</gp:method>
</gp:geopriv> </gp:geopriv>
</status> </status>
<timestamp>2005-07-05T14:49:53+10:00</timestamp> <timestamp>2005-07-05T14:49:53+10:00</timestamp>
</tuple> </tuple>
</presence> </presence>
Geodetic Location Only PIDF-LO
<?xml version="1.0"?> <?xml version="1.0"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf" <presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:pidf="urn:ietf:params:xml:ns:pidf" xmlns:pidf="urn:ietf:params:xml:ns:pidf"
xmlns:cl=" urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr" xmlns:cl=" urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape" xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10" xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gml="http://www.opengis.net/gml" xmlns:gml="http://www.opengis.net/gml"
entity="pres:user@example.com"> entity="pres:user@example.com">
<tuple id="a6fea09"> <tuple id="a6fea09">
<status> <status>
skipping to change at page 30, line 32 skipping to change at page 31, line 32
<gml:pos>-34.4165 150.5337</gml:pos> <gml:pos>-34.4165 150.5337</gml:pos>
<gml:pos>-34.4165 150.5332</gml:pos> <gml:pos>-34.4165 150.5332</gml:pos>
</gml:LinearRing> </gml:LinearRing>
</gml:exterior> </gml:exterior>
</gml:Polygon> </gml:Polygon>
<cl:civilAddress> <cl:civilAddress>
<cl:FLR>2</cl:FLR> <cl:FLR>2</cl:FLR>
</cl:civilAddress> </cl:civilAddress>
</gp:location-info> </gp:location-info>
<gp:usage-rules/> <gp:usage-rules/>
<gp:method>DHCP</gp:method> <gp:method>Wiremap</gp:method>
</gp:geopriv> </gp:geopriv>
</status> </status>
<timestamp>2005-07-05T14:49:53+10:00</timestamp> <timestamp>2005-07-05T14:49:53+10:00</timestamp>
</tuple> </tuple>
</presence> </presence>
Geodetic Location with Civic Floor PIDF-LO
<?xml version="1.0"?> <?xml version="1.0"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf" <presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:pidf="urn:ietf:params:xml:ns:pidf" xmlns:pidf="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10" xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape" xmlns:gs="urn:ietf:params:xml:ns:pidf:geopriv10:geoShape"
xmlns:gml="http://www.opengis.net/gml" xmlns:gml="http://www.opengis.net/gml"
entity="pres:user@example.com"> entity="pres:user@example.com">
<tuple id="a6fea09"> <tuple id="a6fea09">
<status> <status>
<gp:geopriv> <gp:geopriv>
skipping to change at page 31, line 35 skipping to change at page 32, line 35
</gml:LinearRing> </gml:LinearRing>
</gml:exterior> </gml:exterior>
</gml:Polygon> </gml:Polygon>
</gs:base> </gs:base>
<gs:height uom="urn:ogc:def:uom:EPSG::9001"> <gs:height uom="urn:ogc:def:uom:EPSG::9001">
8 8
</gs:height> </gs:height>
</gs:Prism> </gs:Prism>
</gp:location-info> </gp:location-info>
<gp:usage-rules/> <gp:usage-rules/>
<gp:method>DHCP</gp:method> <gp:method>Wiremap</gp:method>
</gp:geopriv> </gp:geopriv>
</status> </status>
<timestamp>2005-07-05T14:49:53+10:00</timestamp> <timestamp>2005-07-05T14:49:53+10:00</timestamp>
</tuple> </tuple>
</presence> </presence>
Rectangular Prism PIDF-LO
Authors' Addresses Authors' Addresses
James Winterbottom James Winterbottom
Andrew Corporation Andrew Corporation
Wollongong Wollongong
NSW Australia NSW Australia
Email: james.winterbottom@andrew.com Email: james.winterbottom@andrew.com
Martin Thomson Martin Thomson
skipping to change at page 33, line 5 skipping to change at page 34, line 5
Email: martin.thomson@andrew.com Email: martin.thomson@andrew.com
Hannes Tschofenig Hannes Tschofenig
Siemens Siemens
Otto-Hahn-Ring 6 Otto-Hahn-Ring 6
Munich, Bavaria 81739 Munich, Bavaria 81739
Germany Germany
Email: Hannes.Tschofenig@siemens.com Email: Hannes.Tschofenig@siemens.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
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 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 The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
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on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 33, line 29 skipping to change at page 34, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity
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 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.
Copyright Statement
Copyright (C) The Internet Society (2006). 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.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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