Internet DRAFT - draft-fossati-core-geo-link-format-attribute
draft-fossati-core-geo-link-format-attribute
Internet Engineering Task Force T. Fossati
Internet-Draft Alcatel-Lucent
Intended status: Standards Track February 12, 2014
Expires: August 16, 2014
A Link-Format Attribute for Locating Things
draft-fossati-core-geo-link-format-attribute-03
Abstract
This memo proposes a new CoAP link format attribute, "geo", that can
be used to associate positioning metadata to a CoAP resource. An
extension to the link format query syntax is also defined to allow
the discovery of resources based on their geo location.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The geo Link Format Attribute . . . . . . . . . . . . . . . . 3
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Encoding Considerations . . . . . . . . . . . . . . . . . . . 4
6. Extended Geo Queries . . . . . . . . . . . . . . . . . . . . 4
6.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.2. Filtering Rules . . . . . . . . . . . . . . . . . . . . . 5
6.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. Security Considerations . . . . . . . . . . . . . . . . . . . 5
10. Normative References . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The ability for a client application to access positioning
information about a sensing resource is crucial in a number of use
cases, e.g. those in which one or more sensor networks provide input
to an emergency handling service (fire, flood, etc.).
This memo proposes a new CoAP link-format attribute, "geo", that can
be used to associate positioning metadata to a CoAP resource, and
make this information available to other endpoints that, directly or
indirectly, participate to CoAP link-format discovery [RFC6690].
This spec reuses the geo URI syntax [RFC5870], which is capable of
describing physical locations in two or three dimensions (also
supporting underground and underwater localisation using negative
numbers) in a simple, reasonably compact, and human readable way.
1.1. Requirements Language
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].
2. Use Cases
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Location-aware applications and location-based services like rescue
systems in devastated areas, seismic networks, gas pipeline
monitoring deployments, fire or flood detection systems, etc., need
to precisely locate the source of sensed stimulus in order to react
in a suitable way. Smart city scenarios, e.g. street lights control,
emergency services, often have similar needs.
3. The geo Link Format Attribute
This section defines a new Web Linking [RFC5988] link-param, "geo",
to be used within the [RFC6690] framework, having the following
syntax:
link-extension = "geo" "=" geo-path
geo-path ; defined in Section 3.3. of RFC 5870
The geo attribute MUST NOT appear more than once in a link.
4. Examples
o A sensor exposing an explicit location resource:
REQ: GET /.well-known/core?geo=*
RES: 2.05 Content
</loc>;geo="52.2047, 0.1368"
o A fire detector somewhere in the Pollino National Park (approx.
10cm accuracy, enough to distinguish trees from each other):
REQ: GET /.well-known/core?geo=*
RES: 2.05 Content
</fire>;ct=0;if="sensor";geo="40.00201,16.34007"
o An underwater current sampler in the sea between Ithaki and
Kefallonia bearing explicit accuracy information (10m):
REQ: GET /.well-known/core?geo=*
RES: 2.05 Content
</water>;ct=0;if="sensor";geo="38.2953,20.6426,-20;u=10"
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5. Encoding Considerations
This specification allows only one CRS, which is WGS-84. There is no
need to set an explicit crslabel when encoding a geo link-format
attribute, since the default value wgs84 applies anyway.
For further encoding consideration, see Section 3.5. of [RFC5870].
6. Extended Geo Queries
The "extended" geo query (xgeo) format allows a client application to
select a capture area, and let endpoints advertise their presence --
by replying to the link-format query -- if they are located within
the specified area.
6.1. Syntax
The syntax for describing the query capture area is based on the "WGS
84 bounding box" defined in section 10.2.2 of [OGC-WSC].
The WGS 84 bounding box is a specialisation of the more general
bounding box concept for use with the WGS 84 geodetic datum, with
latitude and longitude expressed as decimal degrees.
A bounding box is a rectangular area identified by its lower and
upper corners, i.e. the points within the bounding box at which the
value of each coordinate is the algebraic minimum and maximum,
respectively.
For consistency with the geo URI definition, the latitude and
longitude attributes of the upper and lower corners have been
swapped, while the optional 'crs' and 'dimensions' parameters are not
used (their default values are implicitly assumed), which leads to
the following ABNF:
ext-geo-query = "?xgeo=" bounding-box
bounding-box = lower-corner "-" upper-corner
lower-corner = latitude "," longitude
upper-corner = latitude "," longitude
For simplicity, xgeo allows a single bounding box per link-format
query. Therefore, when a search is logically made of multiple boxes
(e.g. at a discontinuity point, or for more complex tessellations),
the querying client shall split it into the appropriate number of
xgeo queries and send them out individually.
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6.2. Filtering Rules
An endpoint which understands xgeo MUST respond to the query if and
only if its latitude and longitude values fall within the bounding
box specified in the query string.
When running the match algorithm, the queried endpoint MUST take into
consideration any accuracy/uncertainty associated with its current
position. Any uncertainty information MUST be returned in a response
if it has been used to compute a positive answer to the corresponding
xgeo query.
6.3. Examples
o An example capture area that would match (among the other) the "/
water" resource in Section 4:
REQ: GET /.well-known/core?xgeo=38.2900,20.6400-38.3000,20.6500
RES[0]: 2.05 Content
</water>;geo="38.2953,20.6426,-20;u=10"
RES[1]: 2.05 Content
</pos>;geo="38.2908,20.6451"
RES[2]: [...]
7. Acknowledgements
Thanks to Keith Drage and Carl Reed for comments and discussions that
have helped shaping this document.
8. IANA Considerations
No formal request at present. However, there is a plan to add a
registry for the namespace of link parameters as part of [RFC5988]
update.
9. Security Considerations
The "geo" link-format attribute shares the same security issues as
any other attribute involved in the discovery process described in
[RFC6690].
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Further to that, the privacy considerations regarding distribution,
protection, usage, retention, and storage of the location information
of the target resource found in [RFC6280] fully apply.
10. Normative References
[OGC-WSC] Whiteside, A. and J. Greenwood, "OGC Web Service Common
Implementation Specification (Version 2.0.0)", April 2010,
<http://http://www.opengeospatial.org/standards/common>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3694] Danley, M., Mulligan, D., Morris, J., and J. Peterson,
"Threat Analysis of the Geopriv Protocol", RFC 3694,
February 2004.
[RFC5870] Mayrhofer, A. and C. Spanring, "A Uniform Resource
Identifier for Geographic Locations ('geo' URI)", RFC
5870, June 2010.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[RFC6280] Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture for
Location and Location Privacy in Internet Applications",
BCP 160, RFC 6280, July 2011.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, August 2012.
Author's Address
Thomas Fossati
Alcatel-Lucent
3 Ely Road
Milton, Cambridge CB24 6DD
UK
Email: thomas.fossati@alcatel-lucent.com
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