Changes (by bernard_aboba@…):
* owner: bernard_aboba@… => martin.thomson@…
Comment:
Here is the complete proposed text for Section 1.2, incorporating Martin's
suggested text as well:
1.2. Resolution and Uncertainty
The DHCP options defined in this document include fields quantifying
the resolution or uncertainty associated with a target location. No
inferences relating to privacy policies can be drawn from either
uncertainty or resolution values.
As utilized in this document, resolution refers to the accuracy of a
reported location, as expressed by the number of valid bits in each
of the Latitude, Longitude and Altitude fields.
In the context of location technology, uncertainty is a
quantification of errors. Any method for determining location is
subject to some sources of error; uncertainty describes the amount of
error that is present. Uncertainty might be the coverage area of a
wireless transmitter, the extent of a building or a single room.
Uncertainty is usually represented as an area within which the target
is located. In this document, each of the three axes can be assigned
an uncertainty value. In effect, this describes a rectangular prism,
which may be used as a coarse representation of a more complex shape
that fits within it. See Section 2.3.2 for more detail on the
correspondence between shapes and uncertainty.
When representing locations from sources that can quantify
uncertainty, the goal is to find the smallest possible rectangular
prism that this format can describe. This is achieved by taking the
minimum and maximum values on each axis and ensuring that the final
encoding covers these points. This increases the region of
uncertainty, but ensures that the region that is described
encompasses the target location.
The DHCPv4 option format defined in this document supports both
resolution and uncertainty parameters. Version 0 of the DHCPv4
option format includes a resolution parameter for each of the
dimensions of location. Since this resolution parameter need not
apply to all dimensions equally, a resolution value is included for
each of the three location elements. Since version 0 of the DHCPv6
option format is not defined, the DHCPv6 option does not support a
resolution parameter. Version 1 of the DHCPv4 and DHCPv6 option
format utilizes an uncertainty parameter. Appendix A describes the
mapping of DHCP option values to GML. Appendix B of this document
provides examples showing the calculation of resolution values.
Appendix C provides an example demonstrating calculation of
uncertainty values.
Since the PIDF-LO format [RFC4119][RFC5491] is used to conveying
location and the associated uncertainty within an emergency call
[Convey], a mechanism is needed to convert the information contained
with the DHCPv4 and DHCPv6 options to PIDF-LO. This document
describes the following conversions:
version 0 to PIDF-LO
version 1 to PIDF-LO
PIDF-LO to version 1
Conversion to PIDF-LO does not increase uncertainty; conversion from
PIDF-LO to version 1 increases uncertainty by less than a factor of 2
in each dimension. Since it is not possible to translate an
arbitrary PIDF-LO to version 0 with a bounded increase in
uncertainty, the conversion to version 0 is not specified. Note also
that in the conversion of version 0 to PIDF-LO it may not always be
possible to produce a PIDF-LO that captures both the location as well
as the uncertainty region surrounding it.
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Reporter: bernard_aboba@… | Owner: martin.thomson@…
Type: defect | Status: new
Priority: major | Milestone: draft-ietf-geopriv-3825bis
Component: rfc3825bis | Version: 1.0
Severity: Submitted WG Document | Keywords:
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Ticket URL: <http://trac.tools.ietf.org/wg/geopriv/trac/ticket/39#comment:2>
geopriv <http://tools.ietf.org/geopriv/>
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