 1/draftietfgeoprivuncertainty01.txt 20140814 13:14:32.330734731 0700
+++ 2/draftietfgeoprivuncertainty02.txt 20140814 13:14:32.398736425 0700
@@ 1,19 +1,19 @@
GEOPRIV M. Thomson
InternetDraft Mozilla
Intended status: Standards Track J. Winterbottom
Expires: January 5, 2015 Unaffiliated
 July 4, 2014
+Expires: February 15, 2015 Unaffiliated
+ August 14, 2014
Representation of Uncertainty and Confidence in PIDFLO
 draftietfgeoprivuncertainty01
+ draftietfgeoprivuncertainty02
Abstract
The key concepts of uncertainty and confidence as they pertain to
location information are defined. Methods for the manipulation of
location estimates that include uncertainty information are outlined.
Status of This Memo
This InternetDraft is submitted in full conformance with the
@@ 22,21 +22,21 @@
InternetDrafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as InternetDrafts. The list of current Internet
Drafts is at http://datatracker.ietf.org/drafts/current/.
InternetDrafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use InternetDrafts as reference
material or to cite them other than as "work in progress."
 This InternetDraft will expire on January 5, 2015.
+ This InternetDraft will expire on February 15, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/licenseinfo) in effect on the date of
publication of this document. Please review these documents
@@ 66,38 +66,38 @@
5. Manipulation of Uncertainty . . . . . . . . . . . . . . . . . 13
5.1. Reduction of a Location Estimate to a Point . . . . . . . 13
5.1.1. Centroid Calculation . . . . . . . . . . . . . . . . 14
5.1.1.1. ArcBand Centroid . . . . . . . . . . . . . . . . 14
5.1.1.2. Polygon Centroid . . . . . . . . . . . . . . . . 15
5.2. Conversion to Circle or Sphere . . . . . . . . . . . . . 17
5.3. ThreeDimensional to TwoDimensional Conversion . . . . . 18
5.4. Increasing and Decreasing Uncertainty and Confidence . . 19
5.4.1. Rectangular Distributions . . . . . . . . . . . . . . 19
5.4.2. Normal Distributions . . . . . . . . . . . . . . . . 20
 5.5. Determining Whether a Location is Within a Given Region . 21
+ 5.5. Determining Whether a Location is Within a Given Region . 20
5.5.1. Determining the Area of Overlap for Two Circles . . . 22
5.5.2. Determining the Area of Overlap for Two Polygons . . 23
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.1. Reduction to a Point or Circle . . . . . . . . . . . . . 23
6.2. Increasing and Decreasing Confidence . . . . . . . . . . 27
6.3. Matching Location Estimates to Regions of Interest . . . 27
6.4. PIDFLO With Confidence Example . . . . . . . . . . . . . 28
7. Confidence Schema . . . . . . . . . . . . . . . . . . . . . . 28
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
8.1. URN SubNamespace Registration for
urn:ietf:params:xml:ns:geopriv:conf . . . . . . . . . . . 30
8.2. XML Schema Registration . . . . . . . . . . . . . . . . . 30
9. Security Considerations . . . . . . . . . . . . . . . . . . . 31
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
11.1. Normative References . . . . . . . . . . . . . . . . . . 31
 11.2. Informative References . . . . . . . . . . . . . . . . . 31
+ 11.2. Informative References . . . . . . . . . . . . . . . . . 32
Appendix A. Conversion Between Cartesian and Geodetic
Coordinates in WGS84 . . . . . . . . . . . . . . . . 33
Appendix B. Calculating the Upward Normal of a Polygon . . . . . 34
B.1. Checking that a Polygon Upward Normal Points Up . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
Location information represents an estimation of the position of a
Target [RFC6280]. Under ideal circumstances, a location estimate
@@ 142,22 +142,23 @@
mathematics, particularly statistics and geometry.
Some terminology is borrowed from [RFC3693] and [RFC6280], in
particular Target.
Mathematical formulae are presented using the following notation: add
"+", subtract "", multiply "*", divide "/", power "^" and absolute
value "x". Precedence is indicated using parentheses.
Mathematical functions are represented by common abbreviations:
square root "sqrt(x)", sine "sin(x)", cosine "cos(x)", inverse cosine
 "acos(x)", tangent "tan(x)", inverse tangent "atan(x)", error
 function "erf(x)", and inverse error function "erfinv(x)".
+ "acos(x)", tangent "tan(x)", inverse tangent "atan(x)", twoargument
+ inverse tangent "atan2(y,x)", error function "erf(x)", and inverse
+ error function "erfinv(x)".
2. A General Definition of Uncertainty
Uncertainty results from the limitations of measurement. In
measuring any observable quantity, errors from a range of sources
affect the result. Uncertainty is a quantification of what is known
about the observed quantity, either through the limitations of
measurement or through inherent variability of the quantity.
Uncertainty is most completely described by a probability
@@ 862,22 +863,21 @@
extrapolated. In particular, the uncertainty can be scaled to meet a
desired confidence or the confidence for a particular region of
uncertainty can be found.
In general, confidence decreases as the region of uncertainty
decreases in size and confidence increases as the region of
uncertainty increases in size. However, this depends on the PDF;
expanding the region of uncertainty for a rectangular distribution
has no effect on confidence without additional information. If the
region of uncertainty is increased during the process of obfuscation
 (see [ID.thomsongeoprivlocationobscuring]), then the confidence
 cannot be increased.
+ (see [RFC6772]), then the confidence cannot be increased.
A region of uncertainty that is reduced in size always has a lower
confidence.
A region of uncertainty that has an unknown PDF shape cannot be
reduced in size reliably. The region of uncertainty can be expanded,
but only if confidence is not increased.
This section makes the simplifying assumption that location
information is symmetrically and evenly distributed in each
@@ 1281,45 +1282,54 @@
This schema defines an element that is used for indicating
confidence in PIDFLO documents.
+
+
+


+
+
+
+
+
+
+
+
8. IANA Considerations
8.1. URN SubNamespace Registration for
urn:ietf:params:xml:ns:geopriv:conf
This section registers a new XML namespace,
"urn:ietf:params:xml:ns:geopriv:conf", as per the guidelines in
[RFC3688].
@@ 1384,70 +1394,71 @@
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
+ [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
+ J. Polk, "Geopriv Requirements", RFC 3693, February 2004.
+
[RFC4119] Peterson, J., "A Presencebased GEOPRIV Location Object
Format", RFC 4119, December 2005.
+ [RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
+ Format for Presence Information Data Format Location
+ Object (PIDFLO)", RFC 5139, February 2008.
+
+ [RFC5491] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
+ Presence Information Data Format Location Object (PIDFLO)
+ Usage Clarification, Considerations, and Recommendations",
+ RFC 5491, March 2009.
+
+ [RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, "Dynamic
+ Host Configuration Protocol Options for CoordinateBased
+ Location Configuration Information", RFC 6225, July 2011.
+
+ [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.
+
11.2. Informative References
[Convert] Burtch, R., "A Comparison of Methods Used in Rectangular
to Geodetic Coordinate Transformations", April 2006.
[GeoShape]
Thomson, M. and C. Reed, "GML 3.1.1 PIDFLO Shape
Application Schema for use by the Internet Engineering
Task Force (IETF)", Candidate OpenGIS Implementation
Specification 06142r1, Version: 1.0, April 2007.
 [ID.thomsongeoprivlocationobscuring]
 Thomson, M., "Obscuring Location", draftthomsongeopriv
 locationobscuring03 (work in progress), June 2011.

[ISO.GUM] ISO/IEC, "Guide to the expression of uncertainty in
measurement (GUM)", Guide 98:1995, 1995.
[NIST.TN1297]
Taylor, B. and C. Kuyatt, "Guidelines for Evaluating and
Expressing the Uncertainty of NIST Measurement Results",
Technical Note 1297, Sep 1994.
 [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
 J. Polk, "Geopriv Requirements", RFC 3693, February 2004.

 [RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
 Format for Presence Information Data Format Location
 Object (PIDFLO)", RFC 5139, February 2008.

[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A LocationtoService Translation
Protocol", RFC 5222, August 2008.
 [RFC5491] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
 Presence Information Data Format Location Object (PIDFLO)
 Usage Clarification, Considerations, and Recommendations",
 RFC 5491, March 2009.

 [RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, "Dynamic
 Host Configuration Protocol Options for CoordinateBased
 Location Configuration Information", RFC 6225, July 2011.

 [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.
+ [RFC6772] Schulzrinne, H., Tschofenig, H., Cuellar, J., Polk, J.,
+ Morris, J., and M. Thomson, "Geolocation Policy: A
+ Document Format for Expressing Privacy Preferences for
+ Location Information", RFC 6772, January 2013.
[Sunday02]
Sunday, D., "Fast polygon area and Newell normal
computation", Journal of Graphics Tools JGT,
7(2):913,2002, 2002,
.
[TS3GPP23_032]
3GPP, "Universal Geographic Area Description (GAD)", 3GPP
TS 23.032 11.0.0, September 2012.
@@ 1496,21 +1507,21 @@
error, is described by the following:
p = sqrt(X^2 + Y^2)
r = sqrt(X^2 + Y^2 + Z^2)
u = atan((1f) * Z * (1 + e'^2 * (1f) * R / r) / p)
latitude = atan((Z + e'^2 * (1f) * R * sin(u)^3)
/ (p  e^2 * R * cos(u)^3))
 longitude = atan(Y / X)
+ longitude = atan2(Y, X)
altitude = sqrt((p  R * cos(u))^2 + (Z  (1f) * R * sin(u))^2)
If the point is near the poles, that is "p < 1", the value for
altitude that this method produces is unstable. A simpler method for
determining the altitude of a point near the poles is:
altitude = Z  R * (1  f)
Appendix B. Calculating the Upward Normal of a Polygon