Geopriv                                                  J. Winterbottom
Internet-Draft                                                M. Thomson
Intended status: Best Current                         Andrew Corporation
Practice                                                October 11, 2007
Expires: April 13, 2008


              Specifying Holes in LoST Service Boundaries
            draft-winterbottom-ecrit-specifying-holes-00.txt

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   Copyright (C) The IETF Trust (2007).













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Abstract

   This document describes how holes can be specified in service
   boundaries.  One means of implementing a solution is described.


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





























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1.  Introduction

   The LoST protocol [I-D.ietf-ecrit-lost] 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





















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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].














































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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


            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.












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              +------- 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.



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   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.















































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














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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 in Figure 7.


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


                        Figure 6: Hexagon with Hole


   <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>43.511 -73.222</gml:pos> <!--C-->
         <gml:pos>43.511 -73.322</gml:pos> <!--B-->
         <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>43.411 -73.322</gml:pos> <!--w-->
       </gml:LinearRing>
     </gml:interior>
   </gml:Polygon>


                    Figure 7: GML for Hexagon with Hole



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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.
   [I-D.schulzrinne-ecrit-lost-sync] describes how LoST servers may
   synchronize with one another and provides examples of possible
   boundary exchanges and data formats.  At the time of writing there is
   no standard format for service provisioning data into a LoST server,
   the format described in [I-D.schulzrinne-ecrit-lost-sync] is used for
   the example in this section.

   Figure 6 shall be 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 area-A is directly represented by the GML encoding provided in
   Figure 7.  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 8.


   <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 8: GML for Area-w

   If this data were in a LoST server and was required in a neighbouring
   LoST server, the data transfer using the format in
   [I-D.schulzrinne-ecrit-lost-sync] would look similar to Figure 9.


   <?xml version="1.0" encoding="UTF-8"?>
     <pushMappingsRequest xmlns="urn:ietf:params:xml:ns:lost1:sync">
      <mappings>
        <mapping sourceId="lost:area-A.nsw.au.example"
          version="1" lastUpdated="2007-11-26T01:00:00Z"
          timeToLive="2007-12-26T01:00:00Z">



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          <displayName xml:lang="en">
            Outer Area Police Department
          </displayName>
          <service>urn:service:sos.police</service>
          <serviceBoundary profile="geodetic-2d">
             <gml:Polygon 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>
               <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>
        </mapping>
        <mapping sourceId="lost:area-w.nsw.au.example"
          version="1" lastUpdated="2007-11-26T01:00:00Z"
          timeToLive="2007-12-26T01:00:00Z">
          <displayName xml:lang="en">
            Inner Area Police Department
          </displayName>
          <service>urn:service:sos.police</service>
          <serviceBoundary profile="geodetic-2d">
             <gml:Polygon 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>



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                 </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>
        </mapping>
       </mappings>
      </pushMappingsRequest>


                 Figure 9: 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 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
   polygons in a separate table and mapped to the primary polygon.  When
   a location is found to map to a polygon, the exceptions table can be
   checked to see if 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 location is found to
   exist in one of the specified holes then the primary polygon can be
   discarded, and searching of the service boundary database can
   continue.















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7.  Security Considerations

   This document does not introduce any security issues
















































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8.  IANA Considerations

   There are no specific IANA considerations for this document.
















































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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.














































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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.

   [I-D.ietf-ecrit-lost]
              Hardie, T., "LoST: A Location-to-Service Translation
              Protocol", draft-ietf-ecrit-lost-06 (work in progress),
              August 2007.

   [I-D.schulzrinne-ecrit-lost-sync]
              Schulzrinne, H., "Synchronizing Location-to-Service
              Translation (LoST) Servers",
              draft-schulzrinne-ecrit-lost-sync-00 (work in progress),
              November 2006.

   [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

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






















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Authors' Addresses

   James Winterbottom
   Andrew Corporation
   PO Box U40
   University of Wollongong, NSW  2500
   AU

   Email: james.winterbottom@andrew.com


   Martin Thomson
   Andrew Corporation
   PO Box U40
   University of Wollongong, NSW  2500
   AU

   Email: martin.thomson@andrew.com

































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