One document matched: draft-ietf-ecrit-specifying-holes-03.xml
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!ENTITY RFC2119 PUBLIC "" "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">
<!ENTITY RFC5222 PUBLIC "" "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5222.xml">
<!ENTITY I-D.ietf-ecrit-lost-sync PUBLIC "" "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-ecrit-lost-sync.xml">
]>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="no"?>
<?rfc iprnotified="no" ?>
<?rfc strict="yes" ?>
<?rfc toc="yes" ?>
<rfc category="bcp" ipr="trust200902">
<front>
<title abbrev="Service Boundary Holes">Specifying Holes in LoST Service Boundaries</title>
<author initials="J." surname="Winterbottom" fullname="James Winterbottom">
<organization>Andrew Corporation</organization>
<address>
<postal>
<street>Andrew Building (39)</street>
<street>Wollongong University Campus</street>
<street>Northfields Avenue</street>
<city>Wollongong</city>
<region>NSW</region>
<code>2522</code>
<country>AU</country>
</postal>
<email>james.winterbottom@andrew.com</email>
</address>
</author>
<author initials="M." surname="Thomson" fullname="Martin Thomson">
<organization>Andrew Corporation</organization>
<address>
<postal>
<street>Andrew Building (39)</street>
<street>Wollongong University Campus</street>
<street>Northfields Avenue</street>
<city>Wollongong</city>
<region>NSW</region>
<code>2522</code>
<country>AU</country>
</postal>
<email>martin.thomson@andrew.com</email>
</address>
</author>
<date month="March" year="2010"/>
<area>Application</area>
<workgroup>ECRIT</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<t>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.
</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>The LoST protocol <xref target="RFC5222"/> maps service and locations to destination addresses. A LoST server 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.
</t>
<t>This document describes the RECOMMENDED approach to specifying holes in service boundaries defined using a GML encoding for the polygons and their internal elements (holes).
</t>
<figure anchor="fig1" title="Holes in a Polygon">
<artwork><![CDATA[
o--------------o
/ \
/ /\ \
/ + +-----+ \
o | Hole \ o
| | 1 / |
| +-------+ |<--- Primary Polygon
| +-------+ |
| / Hole | |
o \ 2 | o
\ +-----+ + /
\ \/ /
\ /
o--------------o
]]>
</artwork>
</figure>
<t>This document describes a profile of <xref target="ISO-19107">Geographic Markup Language (GML)</xref> polygons that constrains their representation when used for describing service boundaries.
</t>
<t>The working group considered that the types of regions described in this memo could be represented in various ways as polygons without holes, but concluded on the recommendations here to avoid potential problems with the arbitrary division of regions and to align with existing geospatial system practices.
</t>
</section>
<section anchor="terminology" title="Terminology">
<t>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 <xref target="RFC2119"/>.
</t>
</section>
<section title="Specifying Holes">
<t>Holes related to an exterior boundary polygon MUST adhere to the following rules:
<list style="format Rule %d: " counter="holerules">
<t>Two holes MUST NOT have more than one point of intersection.</t>
</list>
</t>
<t>If two or more holes overlap or share a common boundary then these represent a single hole. 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.</t>
<figure anchor="fig2" title="Hole Specification with Boundary Sharing">
<artwork><![CDATA[
o--------------o o--------------o
/ \ / \
/ /\ \ / /\ \
/ + +-----+ \ / + +-----+ \
o | Hole \ o o | \ o
| | 1 \ | | | One \ |
| +-+-------+ | =========> | +-+ Hole + |
| / Hole | | | / | |
o \ 2 | o o \ | o
\ +-----+ + / \ +-----+ + /
\ \/ / \ \/ /
\ / \ /
o--------------o o--------------o
Incorrect Correct
]]>
</artwork>
</figure>
<t>
<list style="format Rule %d: " counter="holerules">
<t>A polygon MUST describe a contiguous region.
</t>
</list>
</t>
<t>If a hole overlaps with the outer boundary, or it shares part of a side with the outer boundary, then it has an inlet and it MUST be expressed without the hole.
</t>
<figure anchor="inletspec" title="Specification of an Inlet">
<artwork><![CDATA[
+------- 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
]]>
</artwork>
</figure>
<t>If a hole touches the outer boundary in two places, the region MUST be expressed as two separate polygons.
</t>
<figure anchor="multi-intersect" title="Specification of Hole with Multiple Outer-Boundary Intersections">
<artwork><![CDATA[
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
Incorrect Correct
]]>
</artwork>
</figure>
<t> Similarly, a polygon that is enclosed entirely within a hole from another polygon (i.e., an "island") is a separate polygon.
</t>
<figure anchor="island" title="Holes With Enclosed Polygon (Island)">
<artwork><![CDATA[
o--------------o
/ \
/ +--------------+ \
/ |%%%%%%%%%%%%%%| \
o |%%o--------o%%| o
| |%/ Island \%| |
| |%\ /%| |
| |%%o--------o%%| |
o |%%%%%%%%%%%%%%| o
\ +--------------+ /
\ /
\ /
o--------------o
]]>
</artwork>
</figure>
<t>
<list style="format Rule %d: " counter="holerules">
<t>A hole MUST be formed from a legal linear ring in accordance with <xref target="geoshape"/>, except that points are specified in a clockwise direction.</t>
</list>
</t>
<t>Holes are specified in clockwise direction so that the upward normal is opposed to the upward normal of the exterior boundary of the polygon. Note that <xref target="geoshape"/> stipulates that exterior boundaries are specified in anti-clockwise order.</t>
<t>There is no restriction on the number of points that are used to express the perimeter of either exterior or interior boundaries.
</t>
</section>
<section title="GML Polygons">
<t>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 <xref target="exhex"/>.
</t>
<figure anchor="exhex" title="Hexagon and Associated GML">
<artwork><![CDATA[
F--------------E
/ \
/ \
/ \
A D
\ /
\ /
\ /
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> <!--B-->
<gml:pos>43.111 -73.222</gml:pos> <!--C-->
<gml:pos>43.311 -73.122</gml:pos> <!--D-->
<gml:pos>43.411 -73.222</gml:pos> <!--E-->
<gml:pos>43.411 -73.322</gml:pos> <!--F-->
<gml:pos>43.311 -73.422</gml:pos> <!--A-->
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
]]>
</artwork>
</figure>
<t>Note that polygon vertices in <xref target="exhex"/> are expressed using <pos> elements for clarity. The vertices can also be expressed using a <posList> element.
</t>
</section>
<section title="Holes in GML Polygons">
<t>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 <xref target="holehex"/> is represented by the 4 points of the interior boundary specified by (w,z,y,x).
</t>
<figure anchor="holehex" title="Hexagon with Hole">
<artwork><![CDATA[
F-------------E
/ \
/ w-------------x \
/ |/////////////| \
A |/////////////| D
\ |/////////////| /
\ z-------------y /
\ /
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> <!--B-->
<gml:pos>43.111 -73.222</gml:pos> <!--C-->
<gml:pos>43.311 -73.122</gml:pos> <!--D-->
<gml:pos>43.511 -73.222</gml:pos> <!--E-->
<gml:pos>43.511 -73.322</gml:pos> <!--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>43.411 -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>
]]>
</artwork>
</figure>
</section>
<section title="Service Boundary Specification and Selection Algorithm">
<t>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.
</t>
<t><xref target="holehex"/> 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. Furthermore, area-A is directly represented by the GML encoding provided in <xref target="holehex"/>. 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 <xref target="area-w"/> (note the reversal of the vertices).
</t>
<figure anchor="area-w" title="GML for Area-w">
<artwork><![CDATA[
<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>
]]>
</artwork>
</figure>
<t>Service mappings for these boundaries might be provided by a LoST server in the form shown in <xref target="lost-services"/>.
</t>
<figure anchor="lost-services" title="Service Boundary Specifications">
<artwork><![CDATA[
<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</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>
</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</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>
</mapping>
]]>
</artwork>
</figure>
<t>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. Using interior boundaries makes support for this operation easy, while allowing an arbitrary number of holes in a service boundary to be specified.
</t>
<t>Each polygon is stored in the geospatial database and mapped to a service URN and destination URI. Many geospatial databases natively support polygons with interior exclusions. Without native support, interior boundaries can be stored against the polygon and can checked separately. A location falls within the area described by a polygon if it is within the exterior boundary and not within any interior boundary.
</t>
<t>In the above example, if a location falls within the interior boundary, it maps to the "Inner Area Police" service; likewise, if a location falls within the exterior boundary, but not within the interior boundary, it maps to the "Outer Area Police" service.
</t>
</section>
<section anchor="security-considerations" title="Security Considerations">
<t>Constraining the form of a polygon representation as described in this document does not introduce new security considerations.
</t>
<!-- <t>However, using polygons to describe LoST service boundaries can have the following concerns:
<list style="symbols">
<t>Precise service boundaries with holes can have large numbers of points. This results in LoST responses of significant size and complexity.
</t>
<t>A LoST server might not want to reveal service boundaries to clients.
</t>
</list>
</t>
<t>Both these cases can be addressed by providing smaller, simpler service boundary polygon in LoST responses. This smaller polygon MUST fit within the actual service boundary. This is possible because a LoST server is not required to provide a precise service boundary. The service boundary need only indicate an area within which the service mapping does not change.
</t>
-->
</section>
<section anchor="iana" title="IANA Considerations">
<t>This document has no IANA actions.
</t>
<t>[RFC Editor: please remove this section prior to publication.]
</t>
</section>
<section title="Acknowledgements">
<t>Thanks to Carl Reed for input provided to the list some months back and for reviewing this document. Thanks to Michael Haberler for suggesting that such a specification is required. Thanks to Avery Penniston for review and feedback.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
&RFC5222;
<reference anchor="geoshape">
<front>
<title abbrev="Geo-Shape">GML 3.1.1 PIDF-LO Shape Application Schema for use by the
Internet Engineering Task Force (IETF)</title>
<author initials="M." surname="Thomson" fullname="Martin Thomson">
<organization>Andrew Corporation</organization>
</author>
<author initials="C." surname="Reed" fullname="Carl Reed, PhD.">
<organization>Open Geospatial Consortium Inc.</organization>
</author>
<date month="April" day="10" year="2007"/>
</front>
<seriesInfo name="Candidate OpenGIS Implementation Specification"
value="06-142r1, Version: 1.0"/>
</reference>
</references>
<references title="Informative References">
&I-D.ietf-ecrit-lost-sync;
<reference anchor="ISO-19107">
<front>
<title abbrev="ISO-19107">Geographic information - Spatial Schema</title>
<author>
<organization>ISO</organization>
</author>
<date day="1" month="5" year="2003"/>
</front>
<seriesInfo name="ISO Standard"
value="19107, First Edition"/>
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 13:57:03 |