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2 ECRIT J. Winterbottom
3 Internet-Draft M. Thomson
4 Intended status: BCP Andrew Corporation
5 Expires: September 9, 2010 March 8, 2010
7 Specifying Holes in LoST Service Boundaries
8 draft-ietf-ecrit-specifying-holes-02
10 Abstract
12 This document describes how holes can be specified in geodetic
13 service boundaries. One means of implementing a search solution in a
14 service database, such as one might provide with a LoST server, is
15 described.
17 Status of this Memo
19 This Internet-Draft is submitted to IETF in full conformance with the
20 provisions of BCP 78 and BCP 79.
22 Internet-Drafts are working documents of the Internet Engineering
23 Task Force (IETF), its areas, and its working groups. Note that
24 other groups may also distribute working documents as Internet-
25 Drafts.
27 Internet-Drafts are draft documents valid for a maximum of six months
28 and may be updated, replaced, or obsoleted by other documents at any
29 time. It is inappropriate to use Internet-Drafts as reference
30 material or to cite them other than as "work in progress."
32 The list of current Internet-Drafts can be accessed at
33 http://www.ietf.org/ietf/1id-abstracts.txt.
35 The list of Internet-Draft Shadow Directories can be accessed at
36 http://www.ietf.org/shadow.html.
38 This Internet-Draft will expire on September 9, 2010.
40 Copyright Notice
42 Copyright (c) 2010 IETF Trust and the persons identified as the
43 document authors. All rights reserved.
45 This document is subject to BCP 78 and the IETF Trust's Legal
46 Provisions Relating to IETF Documents
47 (http://trustee.ietf.org/license-info) in effect on the date of
48 publication of this document. Please review these documents
49 carefully, as they describe your rights and restrictions with respect
50 to this document. Code Components extracted from this document must
51 include Simplified BSD License text as described in Section 4.e of
52 the Trust Legal Provisions and are provided without warranty as
53 described in the BSD License.
55 Table of Contents
57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
59 3. Specifying Holes . . . . . . . . . . . . . . . . . . . . . . . 5
60 4. GML Polygons . . . . . . . . . . . . . . . . . . . . . . . . . 8
61 5. Holes in GML Polygons . . . . . . . . . . . . . . . . . . . . 9
62 6. Service Boundary Specification and Selection Algorithm . . . . 10
63 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
64 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
65 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
66 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
67 10.1. Normative References . . . . . . . . . . . . . . . . . . 16
68 10.2. Informative References . . . . . . . . . . . . . . . . . 16
69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
71 1. Introduction
73 The LoST protocol [RFC5222] describes a protocol that's primary
74 purpose is to map service and locations to destination addresses.
75 LoST does this by provisioning boundary maps or areas against service
76 URNs. The boundary is a polygon made up of sets of geodetic
77 coordinates specifying an enclosed area. In some circumstances an
78 area enclosed by a polygon, also known as an exterior polygon, may
79 contain exception areas, or holes, that for the same service must
80 yield a different destination to that described by the larger area.
81 This document describes how holes SHOULD be specified in service
82 boundaries defined using a GML encoding for the polygons and their
83 internal elements (holes). GML polygons are based on elements
84 defined in [ISO-19107].
86 o--------------o
87 / \
88 / /\ \
89 / + +-----+ \
90 o | Hole \ o
91 | | 1 / |
92 | +-------+ |<--- Primary Polygon
93 | +-------+ |
94 | / Hole | |
95 o \ 2 | o
96 \ +-----+ + /
97 \ \/ /
98 \ /
99 o--------------o
101 Figure 1: Holes in a Polygon
103 2. Terminology
105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
107 document are to be interpreted as described in [RFC2119].
109 3. Specifying Holes
111 Holes related to an exterior boundary polygon MUST adhere to the
112 following rules:
114 Rule 1: Two holes MUST NOT have more than one point of
115 intersection. If two or more holes share a common set of
116 boundaries then to the primary polygon these represent a
117 single hole in the service. The internal elements (holes)
118 should have common boundaries removed and a single hole
119 created irrespective of whether the excluded area is itself
120 made up of multiple service boundaries.
122 o--------------o o--------------o
123 / \ / \
124 / /\ \ / /\ \
125 / + +-----+ \ / + +-----+ \
126 o | Hole \ o o | \ o
127 | | 1 \ | | | One \ |
128 | +-+-------+ | =========> | +-+ Hole + |
129 | / Hole | | | / | |
130 o \ 2 | o o \ | o
131 \ +-----+ + / \ +-----+ + /
132 \ \/ / \ \/ /
133 \ / \ /
134 o--------------o o--------------o
136 Incorrect Correct
138 Figure 2: Incorrect Hole Specification with Boundary Sharing
140 Rule 2: A hole MUST NOT have more than one point of intersection
141 with the outer-boundary of the primary (exterior) polygon.
142 If more than one point of intersection occurs the primary
143 polygon is either doesn't have a hole, it has an inlet as
144 in Figure 3, or the primary polygon SHOULD be expressed as
145 two polygons as in Figure 4.
147 +------- Inlet
148 |
149 v
150 o---+-----+----o o---o o----o
151 / |%%%%%| \ / | | \
152 / /%%%%%%| \ / / | \
153 / +%%%%%%%| \ / o o \
154 o |%%%%%%%%\ o o | \ o
155 | |%%%%%%%%%\ | | | \ |
156 | +-+%%%%%%%%+ | ========> | o-o o |
157 | /%%%%%%%%| | | / | |
158 o \%%%%%%%%| o o \ | o
159 \ +-----+ + / \ o-----o o /
160 \ \/ / \ \/ /
161 \ / \ /
162 o--------------o o--------------o
164 Incorrect Correct
166 Figure 3: Correct Specification of an Inlet
168 A--q-----------B A-q q----------B
169 / | | \ / | | \
170 / | | \ / | | \
171 / z r-----s \ / P z r-----s P \
172 H | \ C H o | \ o C
173 | | One \ | | l | \ l |
174 | y-x Hole t | ========> | y y-x t y |
175 | / | | | g / | g |
176 G \ | D G o \ | o D
177 \ / v---u / \ n / v---u n /
178 \ \ / / \ 1 \ / 2 /
179 \ \ / / \ \ / /
180 F-----w--------E F-----w w--------E
182 1 Polgon with a 2 Polygons that map
183 Dividing Hole to the same service
185 Figure 4: Correct Specification of Hole with Multiple Outer-Boundary
186 Intersections
188 Similarly, a polygon containing a hole with an island must be
189 represented as two polygons mapping to the same service.
191 Rule 3: A hole MUST be a legal polygon in accordance with the
192 geoshape specification [geoshape]. There is no restriction
193 on the number of points that may be used to express the
194 perimeter of the hole.
196 4. GML Polygons
198 The GML encoding of a polygon defines a enclosed exterior boundary,
199 with the first and last points of boundary being the same. Consider
200 the example in Figure 5.
202 B--------------C
203 / \
204 / \
205 / \
206 A D
207 \ /
208 \ /
209 \ /
210 F--------------E
212
213
214
215 43.311 -73.422
216 43.111 -73.322
217 43.111 -73.222
218 43.311 -73.122
219 43.411 -73.222
220 43.411 -73.322
221 43.311 -73.422
222
223
224
226 Figure 5: Hexagon and Associated GML
228 Note that polygon vertices in Figure 5 are expressed using
229 elements for clarity. The vertices can also be expressed using a
230 element.
232 5. Holes in GML Polygons
234 A hole is specified in the polygon by defining an interior boundary.
235 The points defining the internal boundary define the area represented
236 by the hole in the primary (exterior) polygon. The shaded area in
237 Figure 6 is represented by the 4 points of the interior boundary
238 specified by (w,z,y,x).
240 F-------------E
241 / \
242 / w-------------x \
243 / |/////////////| \
244 A |/////////////| D
245 \ |/////////////| /
246 \ z-------------y /
247 \ /
248 B-------------C
250
251
252
253 43.311 -73.422
254 43.111 -73.322
255 43.111 -73.222
256 43.311 -73.122
257 43.511 -73.222
258 43.511 -73.322
259 43.311 -73.422
260
261
262
263
264 43.411 -73.322
265 43.411 -73.222
266 43.211 -73.222
267 43.211 -73.322
268 43.411 -73.322
269
270
271
273 Figure 6: Hexagon with Hole
275 Interior parts are specified in clockwise direction, such that the
276 upward normal is opposite to the upward normal of the exterior part.
278 6. Service Boundary Specification and Selection Algorithm
280 A service boundary is represented by a polygon that may have many
281 vertices. The enclosed area of the polygon represents the area in
282 which a service, expressed as a service URN, maps to a single URI.
284 Figure 6 is used to illustrate two service boundaries. The first
285 service boundary A->F shall be referred to as area-A, and the second
286 service boundary w->z shall be referred to as area-w. Furthermore,
287 area-A is directly represented by the GML encoding provided in
288 Figure 6. Area-w is represented as a hole in area-A by the interior
289 boundary. Since area-w is also a service boundary, a separate
290 polygon describing this area is also required and is shown in
291 Figure 7 (note the reversal of the vertices).
293
294
295
296 43.411 -73.322
297 43.211 -73.322
298 43.211 -73.222
299 43.411 -73.222
300 43.411 -73.322
301
302
303
305 Figure 7: GML for Area-w
307 If this data were in a LoST server the data mappings may look similar
308 to the example in Figure 8. This is an example only and does not
309 represent actual LoST server provisioning or data transfer records.
310 The example XML will not complie.
312
317 Outer Area Police
318 urn:service:sos.police
319
320
322
323
324 43.311 -73.422
325 43.111 -73.322
326 43.111 -73.222
327 43.311 -73.122
328 43.511 -73.222
329 43.511 -73.322
330 43.311 -73.422
331
332
333
334
335
336 43.411 -73.322
337 43.211 -73.322
338 43.211 -73.222
339 43.411 -73.222
340 43.411 -73.322
341
342
343
344
345 sip:area-A-pd@example.com
346 xmpp:area-A-pd@example.com
347 000
348
349
354 Inner Area Police
355 urn:service:sos.police
356
357
359
360
361 43.411 -73.322
362 43.211 -73.322
363 43.211 -73.222
364 43.411 -73.222
365 43.411 -73.322
366
367
368
369
370 sip:area-w-pd@example.com
371 xmpp:area-w-pd@example.com
372 000
374
376 Figure 8: Service Boundary Specifications
378 It is considered likely that LoST servers will need to provide
379 responses sufficiently quickly to allow real-time queries to be
380 performed as part of an emergency call routing flow. It is for this
381 reason that databases supporting native geospatial query techniques
382 are desirable and that service boundary specifications that are
383 easily mapped to internal data structures are preferred. Using
384 interior boundaries makes support for this operation easy, while
385 allowing an arbitrary number of holes in a service boundary to be
386 specified.
388 Each polygon is stored in the geospatial database and mapped to a
389 service URN and destination URI. Many geospatial databases natively
390 support polygons with interior exclusions. Without native support,
391 interior boundaries can be stored against the polygon and can checked
392 separately. A location falls within the area described by a polygon
393 if it is within the exterior boundary and not within any interior
394 boundary.
396 7. Security Considerations
398 This document does not introduce any security issues.
400 8. IANA Considerations
402 There are no specific IANA considerations for this document.
404 9. Acknowledgements
406 Thanks to Carl Reed for input provided to the list some months back
407 and for reviewing this document. Thanks to Michael Haberler for
408 suggesting that such a specification is required. Thanks to Avery
409 Penniston for review and feedback.
411 10. References
413 10.1. Normative References
415 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
416 Requirement Levels", BCP 14, RFC 2119, March 1997.
418 [RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
419 Tschofenig, "LoST: A Location-to-Service Translation
420 Protocol", RFC 5222, August 2008.
422 [geoshape]
423 Thomson, M. and C. Reed, "GML 3.1.1 PIDF-LO Shape
424 Application Schema for use by the Internet Engineering
425 Task Force (IETF)", Candidate OpenGIS Implementation
426 Specification 06-142r1, Version: 1.0, April 2007.
428 10.2. Informative References
430 [I-D.ietf-ecrit-lost-sync]
431 Schulzrinne, H. and H. Tschofenig, "Synchronizing
432 Location-to-Service Translation (LoST) Protocol based
433 Service Boundaries and Mapping Elements",
434 draft-ietf-ecrit-lost-sync-09 (work in progress),
435 March 2010.
437 [ISO-19107]
438 ISO, "Geographic information - Spatial Schema", ISO
439 Standard 19107, First Edition, 5 2003.
441 Authors' Addresses
443 James Winterbottom
444 Andrew Corporation
445 Andrew Building (39)
446 Wollongong University Campus
447 Northfields Avenue
448 Wollongong, NSW 2522
449 AU
451 Email: james.winterbottom@andrew.com
453 Martin Thomson
454 Andrew Corporation
455 Andrew Building (39)
456 Wollongong University Campus
457 Northfields Avenue
458 Wollongong, NSW 2522
459 AU
461 Email: martin.thomson@andrew.com