draft-ietf-geopriv-uncertainty-03.txt | draft-ietf-geopriv-uncertainty-04.txt | |||
---|---|---|---|---|

GEOPRIV M. Thomson | GEOPRIV M. Thomson | |||

Internet-Draft Mozilla | Internet-Draft Mozilla | |||

Updates: 3693,4119,5491 (if approved) J. Winterbottom | Updates: 3693,4119,5491 (if approved) J. Winterbottom | |||

Intended status: Standards Track Unaffiliated | Intended status: Standards Track Unaffiliated | |||

Expires: March 20, 2015 September 16, 2014 | Expires: April 25, 2015 October 22, 2014 | |||

Representation of Uncertainty and Confidence in PIDF-LO | Representation of Uncertainty and Confidence in PIDF-LO | |||

draft-ietf-geopriv-uncertainty-03 | draft-ietf-geopriv-uncertainty-04 | |||

Abstract | Abstract | |||

The key concepts of uncertainty and confidence as they pertain to | This document defines key concepts of uncertainty and confidence as | |||

location information are defined. Methods for the manipulation of | they pertain to location information. Methods for the manipulation | |||

location estimates that include uncertainty information are outlined. | of location estimates that include uncertainty information are | |||

outlined. | ||||

This draft normatively updates the definition of location information | This document normatively updates the definition of location | |||

representations defined in RFC 4119 and RFC 5491. It also deprecates | information representations defined in RFC 4119 and RFC 5491. It | |||

related terminology defined in RFC 3693. | also deprecates related terminology defined in RFC 3693. | |||

Status of This Memo | Status of This Memo | |||

This Internet-Draft is submitted in full conformance with the | This Internet-Draft is submitted in full conformance with the | |||

provisions of BCP 78 and BCP 79. | provisions of BCP 78 and BCP 79. | |||

Internet-Drafts are working documents of the Internet Engineering | Internet-Drafts are working documents of the Internet Engineering | |||

Task Force (IETF). Note that other groups may also distribute | Task Force (IETF). Note that other groups may also distribute | |||

working documents as Internet-Drafts. The list of current Internet- | working documents as Internet-Drafts. The list of current Internet- | |||

Drafts is at http://datatracker.ietf.org/drafts/current/. | Drafts is at http://datatracker.ietf.org/drafts/current/. | |||

Internet-Drafts are draft documents valid for a maximum of six months | Internet-Drafts are draft documents valid for a maximum of six months | |||

and may be updated, replaced, or obsoleted by other documents at any | and may be updated, replaced, or obsoleted by other documents at any | |||

time. It is inappropriate to use Internet-Drafts as reference | time. It is inappropriate to use Internet-Drafts as reference | |||

material or to cite them other than as "work in progress." | material or to cite them other than as "work in progress." | |||

This Internet-Draft will expire on March 20, 2015. | This Internet-Draft will expire on April 25, 2015. | |||

Copyright Notice | Copyright Notice | |||

Copyright (c) 2014 IETF Trust and the persons identified as the | Copyright (c) 2014 IETF Trust and the persons identified as the | |||

document authors. All rights reserved. | document authors. All rights reserved. | |||

This document is subject to BCP 78 and the IETF Trust's Legal | This document is subject to BCP 78 and the IETF Trust's Legal | |||

Provisions Relating to IETF Documents | Provisions Relating to IETF Documents | |||

(http://trustee.ietf.org/license-info) in effect on the date of | (http://trustee.ietf.org/license-info) in effect on the date of | |||

publication of this document. Please review these documents | publication of this document. Please review these documents | |||

skipping to change at page 3, line 9 | skipping to change at page 3, line 10 | |||

8.2. XML Schema Registration . . . . . . . . . . . . . . . . . 30 | 8.2. XML Schema Registration . . . . . . . . . . . . . . . . . 30 | |||

9. Security Considerations . . . . . . . . . . . . . . . . . . . 31 | 9. Security Considerations . . . . . . . . . . . . . . . . . . . 31 | |||

10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31 | 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31 | |||

11. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 | 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 | |||

11.1. Normative References . . . . . . . . . . . . . . . . . . 31 | 11.1. Normative References . . . . . . . . . . . . . . . . . . 31 | |||

11.2. Informative References . . . . . . . . . . . . . . . . . 32 | 11.2. Informative References . . . . . . . . . . . . . . . . . 32 | |||

Appendix A. Conversion Between Cartesian and Geodetic | Appendix A. Conversion Between Cartesian and Geodetic | |||

Coordinates in WGS84 . . . . . . . . . . . . . . . . 33 | Coordinates in WGS84 . . . . . . . . . . . . . . . . 33 | |||

Appendix B. Calculating the Upward Normal of a Polygon . . . . . 34 | Appendix B. Calculating the Upward Normal of a Polygon . . . . . 34 | |||

B.1. Checking that a Polygon Upward Normal Points Up . . . . . 35 | B.1. Checking that a Polygon Upward Normal Points Up . . . . . 35 | |||

Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 | Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36 | |||

1. Introduction | 1. Introduction | |||

Location information represents an estimation of the position of a | Location information represents an estimation of the position of a | |||

Target [RFC6280]. Under ideal circumstances, a location estimate | Target [RFC6280]. Under ideal circumstances, a location estimate | |||

precisely reflects the actual location of the Target. For automated | precisely reflects the actual location of the Target. For automated | |||

systems that determine location, there are many factors that | systems that determine location, there are many factors that | |||

introduce errors into the measurements that are used to determine | introduce errors into the measurements that are used to determine | |||

location estimates. | location estimates. | |||

skipping to change at page 4, line 13 | skipping to change at page 4, line 13 | |||

document are to be interpreted as described in [RFC2119]. | document are to be interpreted as described in [RFC2119]. | |||

This document assumes a basic understanding of the principles of | This document assumes a basic understanding of the principles of | |||

mathematics, particularly statistics and geometry. | mathematics, particularly statistics and geometry. | |||

Some terminology is borrowed from [RFC3693] and [RFC6280], in | Some terminology is borrowed from [RFC3693] and [RFC6280], in | |||

particular Target. | particular Target. | |||

Mathematical formulae are presented using the following notation: add | Mathematical formulae are presented using the following notation: add | |||

"+", subtract "-", multiply "*", divide "/", power "^" and absolute | "+", subtract "-", multiply "*", divide "/", power "^" and absolute | |||

value "|x|". Precedence is indicated using parentheses. | value "|x|". Precedence follows established conventions: power | |||

Mathematical functions are represented by common abbreviations: | operations precede multiply and divide, multiply and divide precede | |||

square root "sqrt(x)", sine "sin(x)", cosine "cos(x)", inverse cosine | add and subtract, and parentheses are used to indicate operations | |||

"acos(x)", tangent "tan(x)", inverse tangent "atan(x)", two-argument | that are applied together. Mathematical functions are represented by | |||

inverse tangent "atan2(y,x)", error function "erf(x)", and inverse | common abbreviations: square root "sqrt(x)", sine "sin(x)", cosine | |||

error function "erfinv(x)". | "cos(x)", inverse cosine "acos(x)", tangent "tan(x)", inverse tangent | |||

"atan(x)", two-argument inverse tangent "atan2(y,x)", error function | ||||

"erf(x)", and inverse error function "erfinv(x)". | ||||

2. A General Definition of Uncertainty | 2. A General Definition of Uncertainty | |||

Uncertainty results from the limitations of measurement. In | Uncertainty results from the limitations of measurement. In | |||

measuring any observable quantity, errors from a range of sources | measuring any observable quantity, errors from a range of sources | |||

affect the result. Uncertainty is a quantification of what is known | affect the result. Uncertainty is a quantification of what is known | |||

about the observed quantity, either through the limitations of | about the observed quantity, either through the limitations of | |||

measurement or through inherent variability of the quantity. | measurement or through inherent variability of the quantity. | |||

Uncertainty is most completely described by a probability | Uncertainty is most completely described by a probability | |||

skipping to change at page 8, line 47 | skipping to change at page 8, line 47 | |||

region. When locating a personal device using contemporary location | region. When locating a personal device using contemporary location | |||

determination techniques, the space the device occupies relative to | determination techniques, the space the device occupies relative to | |||

the uncertainty is proportionally quite small. Even where that | the uncertainty is proportionally quite small. Even where that | |||

device is used as a proxy for a person, the proportions change | device is used as a proxy for a person, the proportions change | |||

little. | little. | |||

This assumption is less useful as uncertainty becomes small relative | This assumption is less useful as uncertainty becomes small relative | |||

to the size of the Target of the PIDF-LO (or conversely, as | to the size of the Target of the PIDF-LO (or conversely, as | |||

uncertainty becomes small relative to the Target). For instance, | uncertainty becomes small relative to the Target). For instance, | |||

describing the location of a football stadium or small country would | describing the location of a football stadium or small country would | |||

include a region of uncertainty that is infinitesimally larger than | include a region of uncertainty that is only slightly larger than the | |||

the Target itself. In these cases, much of the guidance in this | Target itself. In these cases, much of the guidance in this document | |||

document is not applicable. Indeed, as the accuracy of location | is not applicable. Indeed, as the accuracy of location determination | |||

determination technology improves, it could be that the advice this | technology improves, it could be that the advice this document | |||

document contains becomes less relevant by the same measure. | contains becomes less relevant by the same measure. | |||

3.2. Representation of Uncertainty and Confidence in PIDF-LO | 3.2. Representation of Uncertainty and Confidence in PIDF-LO | |||

A set of shapes suitable for the expression of uncertainty in | A set of shapes suitable for the expression of uncertainty in | |||

location estimates in the Presence Information Data Format - Location | location estimates in the Presence Information Data Format - Location | |||

Object (PIDF-LO) are described in [GeoShape]. These shapes are the | Object (PIDF-LO) are described in [GeoShape]. These shapes are the | |||

recommended form for the representation of uncertainty in PIDF-LO | recommended form for the representation of uncertainty in PIDF-LO | |||

[RFC4119] documents. | [RFC4119] documents. | |||

The PIDF-LO can contain uncertainty, but does not include an | The PIDF-LO can contain uncertainty, but does not include an | |||

skipping to change at page 10, line 52 | skipping to change at page 10, line 52 | |||

4. Representation of Confidence in PIDF-LO | 4. Representation of Confidence in PIDF-LO | |||

On the whole, a fixed definition for confidence is preferable, | On the whole, a fixed definition for confidence is preferable, | |||

primarily because it ensures consistency between implementations. | primarily because it ensures consistency between implementations. | |||

Location generators that are aware of this constraint can generate | Location generators that are aware of this constraint can generate | |||

location information at the required confidence. Location recipients | location information at the required confidence. Location recipients | |||

are able to make sensible assumptions about the quality of the | are able to make sensible assumptions about the quality of the | |||

information that they receive. | information that they receive. | |||

In some circumstances - particularly with pre-existing systems - | In some circumstances - particularly with pre-existing systems - | |||

location generators might unable to provide location information with | location generators might be unable to provide location information | |||

consistent confidence. Existing systems sometimes specify confidence | with consistent confidence. Existing systems sometimes specify | |||

at 38%, 67% or 90%. Existing forms of expressing location | confidence at 38%, 67% or 90%. Existing forms of expressing location | |||

information, such as that defined in [TS-3GPP-23_032], contain | information, such as that defined in [TS-3GPP-23_032], contain | |||

elements that express the confidence in the result. | elements that express the confidence in the result. | |||

The addition of a confidence element provides information that was | The addition of a confidence element provides information that was | |||

previously unavailable to recipients of location information. | previously unavailable to recipients of location information. | |||

Without this information, a location server or generator that has | Without this information, a location server or generator that has | |||

access to location information with a confidence lower than 95% has | access to location information with a confidence lower than 95% has | |||

two options: | two options: | |||

o The location server can scale regions of uncertainty in an attempt | o The location server can scale regions of uncertainty in an attempt | |||

skipping to change at page 12, line 25 | skipping to change at page 12, line 25 | |||

4.2. Generating Locations with Confidence | 4.2. Generating Locations with Confidence | |||

Location generators SHOULD attempt to ensure that confidence is equal | Location generators SHOULD attempt to ensure that confidence is equal | |||

in each dimension when generating location information. This | in each dimension when generating location information. This | |||

restriction, while not always practical, allows for more accurate | restriction, while not always practical, allows for more accurate | |||

scaling, if scaling is necessary. | scaling, if scaling is necessary. | |||

A confidence element MUST be included with all location information | A confidence element MUST be included with all location information | |||

that includes uncertainty (that is, all forms other than a point). A | that includes uncertainty (that is, all forms other than a point). A | |||

special "unknown" MAY be used if confidence is not known. | special "unknown" is used if confidence is not known. | |||

4.3. Consuming and Presenting Confidence | 4.3. Consuming and Presenting Confidence | |||

The inclusion of confidence that is anything other than 95% presents | The inclusion of confidence that is anything other than 95% presents | |||

a potentially difficult usability problem for applications that use | a potentially difficult usability problem for applications that use | |||

location information. Effectively communicating the probability that | location information. Effectively communicating the probability that | |||

a location is incorrect to a user can be difficult. | a location is incorrect to a user can be difficult. | |||

It is inadvisable to simply display locations of any confidence, or | It is inadvisable to simply display locations of any confidence, or | |||

to display confidence in a separate or non-obvious fashion. If | to display confidence in a separate or non-obvious fashion. If | |||

skipping to change at page 15, line 48 | skipping to change at page 15, line 48 | |||

later in this section for cases where "Nx" or "Ny" are zero. | later in this section for cases where "Nx" or "Ny" are zero. | |||

[ -Ny/p Nx/p 0 ] [ -Ny/p -Nx*Nz/p Nx ] | [ -Ny/p Nx/p 0 ] [ -Ny/p -Nx*Nz/p Nx ] | |||

T = [ -Nx*Nz/p -Ny*Nz/p p ] T' = [ Nx/p -Ny*Nz/p Ny ] | T = [ -Nx*Nz/p -Ny*Nz/p p ] T' = [ Nx/p -Ny*Nz/p Ny ] | |||

[ Nx Ny Nz ] [ 0 p Nz ] | [ Nx Ny Nz ] [ 0 p Nz ] | |||

(Transform) (Reverse Transform) | (Transform) (Reverse Transform) | |||

Figure 3: Recommended Transformation Matrices | Figure 3: Recommended Transformation Matrices | |||

To apply a transform to each point in the polygon, form a matrix from | To apply a transform to each point in the polygon, form a matrix from | |||

the ECEF coordinates and use matrix multiplication to determine the | the Cartesian Earth-Centered, Earth-Fixed (ECEF) coordinates and use | |||

translated coordinates. | matrix multiplication to determine the translated coordinates. | |||

[ -Ny/p Nx/p 0 ] [ x[1] x[2] x[3] ... x[n] ] | [ -Ny/p Nx/p 0 ] [ x[1] x[2] x[3] ... x[n] ] | |||

[ -Nx*Nz/p -Ny*Nz/p p ] * [ y[1] y[2] y[3] ... y[n] ] | [ -Nx*Nz/p -Ny*Nz/p p ] * [ y[1] y[2] y[3] ... y[n] ] | |||

[ Nx Ny Nz ] [ z[1] z[2] z[3] ... z[n] ] | [ Nx Ny Nz ] [ z[1] z[2] z[3] ... z[n] ] | |||

[ x'[1] x'[2] x'[3] ... x'[n] ] | [ x'[1] x'[2] x'[3] ... x'[n] ] | |||

= [ y'[1] y'[2] y'[3] ... y'[n] ] | = [ y'[1] y'[2] y'[3] ... y'[n] ] | |||

[ z'[1] z'[2] z'[3] ... z'[n] ] | [ z'[1] z'[2] z'[3] ... z'[n] ] | |||

Figure 4: Transformation | Figure 4: Transformation | |||

skipping to change at page 22, line 16 | skipping to change at page 22, line 16 | |||

Target is within the region of interest, "Pi", is: | Target is within the region of interest, "Pi", is: | |||

Pi = Co * Ao / Au | Pi = Co * Ao / Au | |||

Given that the area of the region of uncertainty is "Au" and the | Given that the area of the region of uncertainty is "Au" and the | |||

confidence is "Co". | confidence is "Co". | |||

This probability is often input to a decision process that has a | This probability is often input to a decision process that has a | |||

limited set of outcomes; therefore, a threshold value needs to be | limited set of outcomes; therefore, a threshold value needs to be | |||

selected. Depending on the application, different threshold | selected. Depending on the application, different threshold | |||

probabilities might be selected. In the absence of specific | probabilities might be selected. A probability of 50% or greater is | |||

recommendations, this document suggests that the probability be | recommended before deciding that an uncertain value is within a given | |||

greater than 50% before a decision is made. If the decision process | region. If the decision process selects between two or more regions, | |||

selects between two or more regions, as is required by [RFC5222], | as is required by [RFC5222], then the region with the highest | |||

then the region with the highest probability can be selected. | probability can be selected. | |||

5.5.1. Determining the Area of Overlap for Two Circles | 5.5.1. Determining the Area of Overlap for Two Circles | |||

Determining the area of overlap between two arbitrary shapes is a | Determining the area of overlap between two arbitrary shapes is a | |||

non-trivial process. Reducing areas to circles (see Section 5.2) | non-trivial process. Reducing areas to circles (see Section 5.2) | |||

enables the application of the following process. | enables the application of the following process. | |||

Given the radius of the first circle "r", the radius of the second | Given the radius of the first circle "r", the radius of the second | |||

circle "R" and the distance between their center points "d", the | circle "R" and the distance between their center points "d", the | |||

following set of formulas provide the area of overlap "Ao". | following set of formulas provide the area of overlap "Ao". | |||

skipping to change at page 28, line 20 | skipping to change at page 28, line 20 | |||

uncertainty as a circular area. The confidence element (on the line | uncertainty as a circular area. The confidence element (on the line | |||

marked with a comment) indicates that the confidence is 67% and that | marked with a comment) indicates that the confidence is 67% and that | |||

it follows a normal distribution. | it follows a normal distribution. | |||

<pidf:presence | <pidf:presence | |||

xmlns:pidf="urn:ietf:params:xml:ns:pidf" | xmlns:pidf="urn:ietf:params:xml:ns:pidf" | |||

xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model" | xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model" | |||

xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10" | xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10" | |||

xmlns:gs="http://www.opengis.net/pidflo/1.0" | xmlns:gs="http://www.opengis.net/pidflo/1.0" | |||

xmlns:gml="http://www.opengis.net/gml" | xmlns:gml="http://www.opengis.net/gml" | |||

xmlns:con="urn:ietf:params:xml:ns:pidf:geopriv:conf" | xmlns:con="urn:ietf:params:xml:ns:geopriv:conf" | |||

entity="pres:alice@example.com"> | entity="pres:alice@example.com"> | |||

<dm:device id="sg89ab"> | <dm:device id="sg89ab"> | |||

<pidf:status> | <pidf:status> | |||

<gp:geopriv> | <gp:geopriv> | |||

<gp:location-info> | <gp:location-info> | |||

<gs:Circle srsName="urn:ogc:def:crs:EPSG::4326"> | <gs:Circle srsName="urn:ogc:def:crs:EPSG::4326"> | |||

<gml:pos>42.5463 -73.2512</gml:pos> | <gml:pos>42.5463 -73.2512</gml:pos> | |||

<gs:radius uom="urn:ogc:def:uom:EPSG::9001"> | <gs:radius uom="urn:ogc:def:uom:EPSG::9001"> | |||

850.24 | 850.24 | |||

</gs:radius> | </gs:radius> | |||

skipping to change at page 31, line 12 | skipping to change at page 31, line 12 | |||

Schema: The XML for this schema can be found as the entirety of | Schema: The XML for this schema can be found as the entirety of | |||

Section 7 of this document. | Section 7 of this document. | |||

9. Security Considerations | 9. Security Considerations | |||

This document describes methods for managing and manipulating | This document describes methods for managing and manipulating | |||

uncertainty in location. No specific security concerns arise from | uncertainty in location. No specific security concerns arise from | |||

most of the information provided. The considerations of [RFC4119] | most of the information provided. The considerations of [RFC4119] | |||

all apply. | all apply. | |||

A thorough treatment of the privacy implications of describing | ||||

location information are discussed in [RFC6280]. Including | ||||

uncertainty information increases the amount of information | ||||

available; and altering uncertainty is not an effective privacy | ||||

mechanism. | ||||

Providing uncertainty and confidence information can reveal | Providing uncertainty and confidence information can reveal | |||

information about the process by which location information is | information about the process by which location information is | |||

generated. For instance, it might reveal information that could be | generated. For instance, it might reveal information that could be | |||

used to infer that a user is using a mobile device with a GPS, or | used to infer that a user is using a mobile device with a GPS, or | |||

that a user is acquiring location information from a particular | that a user is acquiring location information from a particular | |||

network-based service. A Rule Maker might choose to remove | network-based service. A Rule Maker might choose to remove | |||

uncertainty-related fields from a location object in order to protect | uncertainty-related fields from a location object in order to protect | |||

this information; though it is noted that this information might not | this information. Note however that information might not be | |||

be perfectly protected due to difficulties associated with location | perfectly protected due to difficulties associated with location | |||

obfuscation, as described in Section 13.5 of [RFC6772]. | obfuscation, as described in Section 13.5 of [RFC6772]. In | |||

particular, increasing uncertainty does not necessarily result in a | ||||

reduction of the information conveyed by the location object. | ||||

Adding confidence to location information risks misinterpretation by | Adding confidence to location information risks misinterpretation by | |||

consumers of location that do not understand the element. This could | consumers of location that do not understand the element. This could | |||

be exploited, particularly when reducing confidence, since the | be exploited, particularly when reducing confidence, since the | |||

resulting uncertainty region might include locations that are less | resulting uncertainty region might include locations that are less | |||

likely to contain the target than the recipient expects. Since this | likely to contain the target than the recipient expects. Since this | |||

sort of error is always a possibility, the impact of this is low. | sort of error is always a possibility, the impact of this is low. | |||

10. Acknowledgements | 10. Acknowledgements | |||

End of changes. 15 change blocks. | ||||

36 lines changed or deleted | | 47 lines changed or added | ||

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