ECRIT                                                    J. Winterbottom
Internet-Draft                                                M. Thomson
Intended status: BCP                                  Andrew Corporation
Expires: April 16, 2009                                 October 13, 2008 September 9, 2010                                 March 8, 2010

              Specifying Holes in LoST Service Boundaries
                draft-ietf-ecrit-specifying-holes-01.txt
                  draft-ietf-ecrit-specifying-holes-02

Abstract

   This document describes how holes can be specified in geodetic
   service boundaries.  One means of implementing a search solution in a
   service database, such as one might provide with a LoST server, is
   described.

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Abstract September 9, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document describes how holes can be specified is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in geodetic
   service boundaries.  One means effect on the date of implementing a search solution in a
   service database, such
   publication of this document.  Please review these documents
   carefully, as one might provide they describe your rights and restrictions with a LoST server, is
   described. respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Specifying Holes . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  GML Polygons . . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Holes in GML Polygons  . . . . . . . . . . . . . . . . . . . .  9
   6.  Service Boundary Specification and Selection Algorithm . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 16
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
   Intellectual Property and Copyright Statements . . . . . . . . . . 18

1.  Introduction

   The LoST protocol [RFC5222] describes a protocol that's primary
   purpose is to map service and locations to destination addresses.
   LoST does this by provisioning boundary maps or areas against service
   URNs.  The boundary is a polygon made up of sets of geodetic
   coordinates specifying an enclosed area.  In some circumstances an
   area enclosed by a polygon, also known as an exterior polygon, may
   contain exception areas, or holes, that for the same service must
   yield a different destination to that described by the larger area.
   This document describes how holes SHOULD be specified in service
   boundaries defined using a GML encoding for the polygons and their
   internal elements (holes).  GML polygons are based on elements
   defined in [ISO-19107].

       o--------------o
      /                \
     /    /\            \
    /    + +-----+       \
   o     |  Hole  \       o
   |     |    1   /       |
   |     +-------+        |<--- Primary Polygon
   |        +-------+     |
   |       /  Hole  |     |
   o       \   2    |     o
    \       +-----+ +    /
     \             \/   /
      \                /
       o--------------o

                       Figure 1: Holes in a Polygon

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].

3.  Specifying Holes

   Holes related to an exterior boundary polygon MUST adhere to the
   following rules:

   Rule 1:   Two holes MUST NOT have more than one point of
             intersection.  If two or more holes share a common set of
             boundaries then to the primary polygon these represent a
             single hole in the service.  The internal elements (holes)
             should have common boundaries removed and a single hole
             created irrespective of whether the excluded area is itself
             made up of multiple service boundaries.

       o--------------o                      o--------------o
      /                \                    /                \
     /    /\            \                  /    /\            \
    /    + +-----+       \                /    + +-----+       \
   o     |  Hole  \       o              o     |        \       o
   |     |    1    \      |              |     |  One    \      |
   |     +-+-------+      |  =========>  |     +-+  Hole +      |
   |       /  Hole  |     |              |       /        |     |
   o       \   2    |     o              o       \        |     o
    \       +-----+ +    /                \       +-----+ +    /
     \             \/   /                  \             \/   /
      \                /                    \                /
       o--------------o                      o--------------o

          Incorrect                              Correct

       Figure 2: Incorrect Hole Specification with Boundary Sharing

   Rule 2:   A hole MUST NOT have more than one point of intersection
             with the outer-boundary of the primary (exterior) polygon.
             If more than one point of intersection occurs the primary
             polygon is either doesn't have a hole, it has an inlet as
             in Figure 3, or the primary polygon SHOULD be expressed as
             two polygons as in Figure 4.

              +------- Inlet
              |
              v
       o---+-----+----o                     o---o     o----o
      /    |%%%%%|     \                   /    |     |     \
     /    /%%%%%%|      \                 /    /      |      \
    /    +%%%%%%%|       \               /    o       o       \
   o     |%%%%%%%%\       o             o     |        \       o
   |     |%%%%%%%%%\      |             |     |         \      |
   |     +-+%%%%%%%%+     |  ========>  |     o-o        o     |
   |       /%%%%%%%%|     |             |       /        |     |
   o       \%%%%%%%%|     o             o       \        |     o
    \       +-----+ +    /               \       o-----o o    /
     \             \/   /                 \             \/   /
      \                /                   \                /
       o--------------o                     o--------------o

          Incorrect                             Correct

                Figure 3: Correct Specification of an Inlet

       A--q-----------B                     A-q   q----------B
      /  | |           \                   /  |   |           \
     /   | |            \                 /   |   |            \
    /    z r-----s       \               / P  z   r-----s   P   \
   H     |        \       C             H  o  |          \   o   C
   |     |  One    \      |             |  l  |           \   l  |
   |     y-x  Hole  t     |  ========>  |  y  y-x          t  y  |
   |       /        |     |             |  g    /          |  g  |
   G       \        |     D             G  o    \          |  o  D
    \      /    v---u    /               \ n    /      v---u  n /
     \     \   /        /                 \  1  \     /      2 /
      \     \ /        /                   \     \   /        /
       F-----w--------E                     F-----w w--------E

         1 Polgon with a                     2 Polygons that map
          Dividing Hole                      to the same service

   Figure 4: Correct Specification of Hole with Multiple Outer-Boundary
                               Intersections

   Similarly, a polygon containing a hole with an island must be
   represented as two polygons mapping to the same service.

   Rule 3:   A hole MUST be a legal polygon in accordance with the
             geoshape specification [geoshape].  There is no restriction
             on the number of points that may be used to express the
             perimeter of the hole.

4.  GML Polygons

   The GML encoding of a polygon defines a enclosed exterior boundary,
   with the first and last points of boundary being the same.  Consider
   the example in Figure 5.

       B--------------C
      /                \
     /                  \
    /                    \
   A                      D
    \                    /
     \                  /
      \                /
       F--------------E

   <gml:Polygon srsName="urn:ogc:def:crs:EPSG::4326">
     <gml:exterior>
       <gml:LinearRing>
         <gml:pos>43.311 -73.422</gml:pos> <!--A-->
         <gml:pos>43.111 -73.322</gml:pos> <!--F-->
         <gml:pos>43.111 -73.222</gml:pos> <!--E-->
         <gml:pos>43.311 -73.122</gml:pos> <!--D-->
         <gml:pos>43.411 -73.222</gml:pos> <!--C-->
         <gml:pos>43.411 -73.322</gml:pos> <!--B-->
         <gml:pos>43.311 -73.422</gml:pos> <!--A-->
       </gml:LinearRing>
     </gml:exterior>
   </gml:Polygon>

                   Figure 5: Hexagon and Associated GML

   NOTE

   Note that polygon vertices in Figure 5 are expressed using <pos>
   elements for clarity.  The vertices can also be expressed using a
   <posList> element.

5.  Holes in GML Polygons

   A hole is specified in the polygon by defining an interior boundary.
   The points defining the internal boundary define the area represented
   by the hole in the primary (exterior) polygon.  The shaded area in
   Figure 6 is represented by the 4 points of the interior boundary
   specified by (w,z,y,x).

       B-------------C

       F-------------E
      /               \
     / w-------------x \
    /  |/////////////|  \
   A   |/////////////|   D
    \  |/////////////|  /
     \ z-------------y /
      \               /
       F-------------E
       B-------------C

   <gml:Polygon srsName="urn:ogc:def:crs:EPSG::4326">
     <gml:exterior>
       <gml:LinearRing>
         <gml:pos>43.311 -73.422</gml:pos> <!--A-->
         <gml:pos>43.111 -73.322</gml:pos> <!--F--> <!--B-->
         <gml:pos>43.111 -73.222</gml:pos> <!--E--> <!--C-->
         <gml:pos>43.311 -73.122</gml:pos> <!--D-->
         <gml:pos>43.511 -73.222</gml:pos> <!--C--> <!--E-->
         <gml:pos>43.511 -73.322</gml:pos> <!--B--> <!--F-->
         <gml:pos>43.311 -73.422</gml:pos> <!--A-->
       </gml:LinearRing>
     </gml:exterior>
     <gml:interior>
       <gml:LinearRing>
         <gml:pos>43.411 -73.322</gml:pos> <!--w-->
         <gml:pos>43.211 -73.322</gml:pos> <!--z-->
         <gml:pos>43.211 -73.222</gml:pos> <!--y-->
         <gml:pos>43.411 -73.222</gml:pos> <!--x-->
         <gml:pos>43.211 -73.222</gml:pos> <!--y-->
         <gml:pos>43.211 -73.322</gml:pos> <!--z-->
         <gml:pos>43.411 -73.322</gml:pos> <!--w-->
       </gml:LinearRing>
     </gml:interior>
   </gml:Polygon>

                        Figure 6: Hexagon with Hole

   Interior parts are specified in clockwise direction, such that the
   upward normal is opposite to the upward normal of the exterior part.

6.  Service Boundary Specification and Selection Algorithm

   A service boundary is represented by a polygon that may have many
   vertices.  The enclosed area of the polygon represents the area in
   which a service, expressed as a service URN, maps to a single URI.

   Figure 6 shall be is used to illustrate two service boundaries.  The first
   service boundary A->F shall be referred to as area-A, and the second
   service boundary w->z shall be referred to as area-w.  Further
   more  Furthermore,
   area-A is directly represented by the GML encoding provided in
   Figure 6.  Area-w is represented as a hole in area-A by the interior
   boundary.  Since area-w is also a service boundary, a separate
   polygon describing this area is also required and is shown in
   Figure 7. 7 (note the reversal of the vertices).

   <gml:Polygon srsName="urn:ogc:def:crs:EPSG::4326">
     <gml:exterior>
       <gml:LinearRing>
         <gml:pos>43.411 -73.322</gml:pos> <!--w-->
         <gml:pos>43.211 -73.322</gml:pos> <!--z-->
         <gml:pos>43.211 -73.222</gml:pos> <!--y-->
         <gml:pos>43.411 -73.222</gml:pos> <!--x-->
         <gml:pos>43.411 -73.322</gml:pos> <!--w-->
       </gml:LinearRing>
     </gml:exterior>
   </gml:Polygon>

                         Figure 7: GML for Area-w

   If this data were in a LoST server the data mappings may look similar
   to the example in Figure 8.  This is an example only and does not
   represent actual LoST server provisioning or data transfer records.
   The example XML will not complie.

   <?xml version="1.0" encoding="UTF-8"?>
     <entry>
       <name> Outer

     <mapping xmlns="urn:ietf:params:xml:ns:lost1"
              expires="2010-12-25T09:44:33Z"
              lastUpdated="2010-03-08T03:48:22Z"
              source="authoritative.foo.example"
              sourceId="7e3f40b098c711dbb606011111111111">
       <displayName xml:lang="en">Outer Area Police Department </name> Police</displayName>
       <service>urn:service:sos.police</service>
       <serviceBoundary profile="geodetic-2d">
         <gml:Polygon xmlns:gml="http://www.opengis.net/gml"
                      srsName="urn:ogc:def:crs:EPSG::4326">
           <gml:exterior>
             <gml:LinearRing>
               <gml:pos>43.311 -73.422</gml:pos>
               <gml:pos>43.111 -73.322</gml:pos>
               <gml:pos>43.111 -73.222</gml:pos>
               <gml:pos>43.311 -73.122</gml:pos>
               <gml:pos>43.511 -73.222</gml:pos>
               <gml:pos>43.511 -73.322</gml:pos>
               <gml:pos>43.311 -73.422</gml:pos>
             </gml:LinearRing>
           </gml:exterior>
           <!-- this is the service boundary hole -->
           <gml:interior>
             <gml:LinearRing>
               <gml:pos>43.411 -73.322</gml:pos>
               <gml:pos>43.211 -73.322</gml:pos>
               <gml:pos>43.211 -73.222</gml:pos>
               <gml:pos>43.411 -73.222</gml:pos>
               <gml:pos>43.411 -73.322</gml:pos>
             </gml:LinearRing>
           </gml:interior>
         </gml:Polygon>
       </serviceBoundary>
       <uri>sip:area-A-pd@example.com</uri>
       <uri>xmpp:area-A-pd@example.com</uri>
       <serviceNumber>000</serviceNumber>
     </entry>
     <entry>
       <name> Inner
     </mapping>
     <mapping xmlns="urn:ietf:params:xml:ns:lost1"
              expires="2010-12-25T09:44:33Z"
              lastUpdated="2010-03-08T03:48:22Z"
              source="authoritative.foo.example"
              sourceId="7e3f40b098c711dbb606011111111111">
       <displayName xml:lang="en">Inner Area Police Department </name> Police</displayName>
       <service>urn:service:sos.police</service>
       <serviceBoundary profile="geodetic-2d">
         <gml:Polygon xmlns:gml="http://www.opengis.net/gml"
                      srsName="urn:ogc:def:crs:EPSG::4326">
           <gml:exterior>
             <gml:LinearRing>
               <gml:pos>43.411 -73.322</gml:pos>
               <gml:pos>43.211 -73.322</gml:pos>
               <gml:pos>43.211 -73.222</gml:pos>
               <gml:pos>43.411 -73.222</gml:pos>
               <gml:pos>43.411 -73.322</gml:pos>
             </gml:LinearRing>
           </gml:exterior>
         </gml:Polygon>
       </serviceBoundary>
       <uri>sip:area-w-pd@example.com</uri>
       <uri>xmpp:area-w-pd@example.com</uri>
       <serviceNumber>000</serviceNumber>
     </entry>

     </mapping>

                 Figure 8: Service Boundary Specifications

   It is considered likely that LoST servers will need to provide
   responses sufficiently quickly to allow real-time queries to be
   performed as part of an emergency call routing flow.  It is for this
   reason that databases supporting native geospatial query techniques
   are desirable and that service boundary specifications that are
   easily mapped to internal data structures are preferred.  The format
   described in this memo  Using
   interior boundaries makes support for this operation easy, while
   allowing an arbitrary number of holes in a service boundary to be
   specified.

   Each primary polygon is stored in the geospatial database and mapped to a
   service URN and destination URI.  Holes may be stored as  Many geospatial databases natively
   support polygons in a separate table and mapped to the primary polygon.  When
   a location is found to map to a polygon, the exceptions table with interior exclusions.  Without native support,
   interior boundaries can be
   checked to see if stored against the primary polygon contains any coverage holes.
   In general no holes will exist for a service boundary, so this check
   results in almost no overhead and the service mapping can be
   returned.  Where one or more holes are found to exist, the provided
   location is checked against each hole.  If the
   separately.  A location is found to
   exist in one of the specified holes then falls within the primary area described by a polygon can be
   discarded, and searching of
   if it is within the service exterior boundary database can
   continue. and not within any interior
   boundary.

7.  Security Considerations

   This document does not introduce any security issues.

8.  IANA Considerations

   There are no specific IANA considerations for this document.

9.  Acknowledgements

   Thanks to Carl Reed for input provided to the list some months back
   and for reviewing this document.  Thanks also to Michael Haberler for
   suggesting that such a specification is required.  Thanks to Avery
   Penniston for review and feedback.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5222]  Hardie, T., Newton, A., Schulzrinne, H., and H.
              Tschofenig, "LoST: A Location-to-Service Translation
              Protocol", RFC 5222, August 2008.

   [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.

10.2.  Informative References

   [I-D.ietf-ecrit-lost-sync]
              Schulzrinne, H., H. and H. Tschofenig, "Synchronizing
              Location-to-Service Translation (LoST) Servers", draft-ietf-ecrit-lost-sync-00 Protocol based
              Service Boundaries and Mapping Elements",
              draft-ietf-ecrit-lost-sync-09 (work in progress), July 2008.
              March 2010.

   [ISO-19107]
              ISO, "Geographic information - Spatial Schema", ISO
              Standard 19107, First Edition, 5 2003.

Authors' Addresses

   James Winterbottom
   Andrew Corporation
   PO Box U40
   Andrew Building (39)
   Wollongong University of Campus
   Northfields Avenue
   Wollongong, NSW  2500  2522
   AU

   Email: james.winterbottom@andrew.com

   Martin Thomson
   Andrew Corporation
   PO Box U40
   Andrew Building (39)
   Wollongong University of Campus
   Northfields Avenue
   Wollongong, NSW  2500  2522
   AU

   Email: martin.thomson@andrew.com

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