Geopriv H. Tschofenig
Internet-Draft Nokia Siemens Networks
Intended status: Standards Track J. Winterbottom
Expires: September 8, 2009 Andrew Corporation
March 7, 2009
Specifying a Circular Uncertainty Area Using DHCP
draft-tschofenig-geopriv-dhcp-circle-01.txt
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Abstract
This document specifies how a circular area representing the location
of device can be returned using DHCP. The document also shows how
the data returned from DHCP can be encoded into GML for using in a
PIDF-LO in an unambiguous or contentious manner.
This document is a contribution to the ongoing discussion on RFC
3825; it represents one possible solution to address the discussed
issues.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Details and Rationale . . . . . . . . . . . . . . . . . . . . 5
3.1. DHCPv4 Option for a Circular Location . . . . . . . . . . 5
3.2. DHCPv6 Option for a LIS Address . . . . . . . . . . . . . 6
4. Expressing the Circle in GML . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
8. Normative References . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Location provided by GPS device and like generally provide location
information as a point with a degree of uncertainty. This
uncertainty is more often than not expressed as an offset in metres
from the central point, with the resulting location being a circle
when expressed in 2 dimensions, and a sphere when expressed in 3
dimensions. This memo presupposes that locations have been measured,
for example using a GPS, ahead of time and have subsequently been
stored in a wiremap database. Associations between end-devices and
location can be done using DHCP option 82 or other methods where
appropriate.
This document omits an altitude representation based on the
envisioned usage scenario.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Details and Rationale
The intent of this specification is to provide a location to an end-
device so that it can easily represent it as circle in GML in
accordance with PIDF-LO Profile [I-D.ietf-geopriv-pdif-lo-profile].
PIDF-LO Profile relies on geoshape [geoshape] requires all
coordinates to be specified using WGS-84, consequently the
coordinates used in this memo are specified using WGS-84.
GML [gml] uses the ISO 19107 [ISO-19107] definition of a point, and
quotes this as being "0-dimensional geometric primitive, representing
a position. NOTE The boundary of a point is the empty set." At some
point however, it becomes necessary to express the coordinates that
make up the location in bits and bytes. Since the intent is to use
GML as the final representation, the encoding standards and
limitations expressed by GML are used.
GML is an XML language [xml] for expressing location information, and
XML defines mappings between its primative types and standard binary
encodings. The GML point is made up of XML (xsd) doubles, and an XML
double is expressed as an IEEE 754-1985 [IEEE-754-1985] double-
precision floating point number. This means that a latitude or
longitude in GML is expressed as a 64 bit binary number, but in
accordance with the previous definition is interpretted as being zero
dimensional, without area.
The binary encodings provided in this memo express latitude and
longitude values as 64 bit binary floating-point numbers, as defined
in [IEEE-754-1985]. A radius is defined as a positive offset to this
in metres, and is expressed as an unsigned 16 bit integer. This
allows a circle with a radius in the order of 65.5km to be expressed
without difficulty, and for a point with no specified uncertainty to
be provided where the radius is set to zero.
3.1. DHCPv4 Option for a Circular Location
This section defines a DHCP for IPv4 (DHCPv4) option for the point
with radius of uncertainty.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LOC-CIRCLE | Length | Latitude |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude continued |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude Continued | Longitude |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude continued |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude Continued | Radius |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
DHCPv4 Option
LOC-CIRCLE: The IANA assigned option number (TBD).
Length: The length of this option octets (18).
Latitude: 8 octets representing the the latitude of the central
point of a circle, expressed as an [IEEE-754-1985] double.
Longitude: 8 octets representing the the longitude of the central
point of a circle, expressed as an [IEEE-754-1985] double.
Radius: a 16 bit unsigned integer expressing the radius of the
circle in metres.
3.2. DHCPv6 Option for a LIS Address
This section defines a DHCP for IPv6 (DHCPv6) option for the point
with radius of uncertainty. The DHCPv6 option for this parameter is
similarly formatted to the DHCPv4 option.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LOC-CIRCLE | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latitude continued |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Longitude continued |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radius |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
DHCPv6 Option
LOC-CIRCLE: The IANA assigned option number (TBD).
Length: The length of this option in octets (18).
Latitude: 8 octets representing the the latitude of the central
point of a circle, expressed as an [IEEE-754-1985] double.
Longitude: 8 octets representing the the longitude of the central
point of a circle, expressed as an [IEEE-754-1985] double.
Radius: a 16 bit unsigned integer expressing the radius of the
circle in metres.
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4. Expressing the Circle in GML
PIDF-LO Profile [I-D.ietf-geopriv-pdif-lo-profile] describes how a
circle is expressed in GML and included in a PIDF-LO [RFC4119]. The
latitude and longitude components of this encoding form the central
point of the circle.
_d^^^^^^^^^b_
.d'' ``b.
.p' / `q.
.d' Radius-> / `b.
.d' / `b.
:: / ::
:: C ::
:: ^ ::
`p. | .q'
`p. Centre .q'
`b. .d'
`q.. ..p'
^q.........p^
Figure 1: Circle Representation
The XML for the resulting circle is shown in Figure 2 (assuming the
centre is represented as 42.5463 -73.2512) and the radius is 5
meters.
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<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gs="http://www.opengis.net/pidflo/1.0"
xmlns:gml="http://www.opengis.net/gml"
entity="pres: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">
5
</gml:radius>
</gs:Circle>
</gp:location-info>
<usage-rules/>
<method>DHCP</method>
</gp:geopriv>
</status>
</tuple>
</presence>
Figure 2: Resulting XML and PIDF-LO
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5. Security Considerations
The security issues for this document are the same as for RFC 3825
[RFC3825].
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6. IANA Considerations
There are no specific IANA considerations for this document.
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7. Acknowledgements
The authors contribute this document to the ongoing discussion in the
GEOPRIV working group. Still, the authors believe that it would be
necessary to investigate the intended deployment use cases more in
order to evaluate what additional location shapes are likely to be
used and whether there is interest in using DHCP (or lower layer
protocols developed by the IEEE or TIA) for conveying location
information or whether there is more interest to use these protocols
purely to discover a LIS and allow more flexibility with regard to
the supported location shapes.
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8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.ietf-geopriv-pdif-lo-profile]
Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
PIDF-LO Usage Clarification, Considerations and
Recommendations", draft-ietf-geopriv-pdif-lo-profile-14
(work in progress), November 2008.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[RFC3825] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based
Location Configuration Information", RFC 3825, July 2004.
[geoshape]
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 06-142r1, Version: 1.0, April 2007.
[ISO-19107]
ISO, "Geographic information - Spatial Schema", ISO
Standard 19107, First Edition, 5 2003.
[gml] Cox, S., Daisey, P., Lake, R., Portele, C., and A.
Whiteside, "Geographic information - Geography Markup
Language (GML)", OpenGIS 03-105r1, April 2004,
<http://portal.opengeospatial.org/files/
?artifact_id=4700>.
[xml] W3C, "XML Schema Part 2: Datatypes Second Edition",
October 2004, <http://www.w3.org/TR/xmlschema-2/>.
[IEEE-754-1985]
IEEE, "754-1985 IEEE Standard for Binary Floating-Point
Arithmetic", January 2003.
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Authors' Addresses
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
James Winterbottom
Andrew Corporation
PO Box U40
University of Wollongong, NSW 2500
AU
Email: james.winterbottom@andrew.com
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