source: osm/applications/editors/josm/plugins/smed2/src/s57/S57map.java@ 30315

Last change on this file since 30315 was 30315, checked in by malcolmh, 11 years ago

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1/* Copyright 2014 Malcolm Herring
2 *
3 * This is free software: you can redistribute it and/or modify
4 * it under the terms of the GNU General Public License as published by
5 * the Free Software Foundation, version 3 of the License.
6 *
7 * For a copy of the GNU General Public License, see <http://www.gnu.org/licenses/>.
8 */
9
10package s57;
11
12import java.util.*;
13
14import s57.S57obj;
15import s57.S57obj.*;
16import s57.S57att;
17import s57.S57att.*;
18import s57.S57val;
19import s57.S57val.*;
20
21public class S57map {
22
23 public class MapBounds {
24 public double minlat;
25 public double minlon;
26 public double maxlat;
27 public double maxlon;
28 public MapBounds() {
29 minlat = 90;
30 minlon = 180;
31 maxlat = -90;
32 maxlon = -180;
33 }
34 }
35
36 public enum Nflag {
37 ANON, // Edge inner nodes
38 ISOL, // Node not part of Edge
39 CONN, // Edge first and last nodes
40 DPTH // Sounding nodes
41 }
42
43 public class Snode { // All coordinates in map
44 public double lat; // Latitude
45 public double lon; // Longitude
46 public Nflag flg; // Role of node
47
48 public Snode() {
49 flg = Nflag.ANON;
50 lat = 0;
51 lon = 0;
52 }
53 public Snode(double ilat, double ilon) {
54 flg = Nflag.ANON;
55 lat = ilat;
56 lon = ilon;
57 }
58 public Snode(double ilat, double ilon, Nflag iflg) {
59 lat = ilat;
60 lon = ilon;
61 flg = iflg;
62 }
63 }
64
65 public class Dnode extends Snode { // All depth soundings
66 public double val; // Sounding value
67
68 public Dnode() {
69 flg = Nflag.DPTH;
70 lat = 0;
71 lon = 0;
72 val = 0;
73 }
74 public Dnode(double ilat, double ilon, double ival) {
75 flg = Nflag.DPTH;
76 lat = ilat;
77 lon = ilon;
78 val = ival;
79 }
80 }
81
82 public class Edge { // A polyline segment
83 public long first; // First CONN node
84 public long last; // Last CONN node
85 public ArrayList<Long> nodes; // Inner ANON nodes
86
87 public Edge() {
88 first = 0;
89 last = 0;
90 nodes = new ArrayList<Long>();
91 }
92 }
93
94 public enum Rflag {
95 UNKN, MASTER, SLAVE
96 }
97
98 public class Reln {
99 public long id;
100 public Rflag reln;
101 public Reln(long i, Rflag r) {
102 id = i;
103 reln = r;
104 }
105 }
106
107 public class RelTab extends ArrayList<Reln> {
108 public RelTab() {
109 super();
110 }
111 }
112
113 public class ObjTab extends HashMap<Integer, AttMap> {
114 public ObjTab() {
115 super();
116 }
117 }
118
119 public class ObjMap extends EnumMap<Obj, ObjTab> {
120 public ObjMap() {
121 super(Obj.class);
122 }
123 }
124
125 public class AttMap extends HashMap<Att, AttVal<?>> {
126 public AttMap() {
127 super();
128 }
129 }
130
131 public class NodeTab extends HashMap<Long, Snode> {
132 public NodeTab() {
133 super();
134 }
135 }
136
137 public class EdgeTab extends HashMap<Long, Edge> {
138 public EdgeTab() {
139 super();
140 }
141 }
142
143 public class FtrMap extends EnumMap<Obj, ArrayList<Feature>> {
144 public FtrMap() {
145 super(Obj.class);
146 }
147 }
148
149 public class FtrTab extends HashMap<Long, Feature> {
150 public FtrTab() {
151 super();
152 }
153 }
154
155 public class Prim { // Spatial element
156 public long id; // Snode ID for POINTs, Edge ID for LINEs & AREAs)
157 public boolean forward; // Direction of vector used (LINEs & AREAs)
158 public boolean outer; // Exterior/Interior boundary (AREAs)
159 public Prim() {
160 id = 0; forward = true; outer = true;
161 }
162 public Prim(long i) {
163 id = i; forward = true; outer = true;
164 }
165 public Prim(long i, boolean o) {
166 id = i; forward = true; outer = o;
167 }
168 public Prim(long i, boolean f, boolean o) {
169 id = i; forward = f; outer = o;
170 }
171 }
172
173 public class Comp { // Composite spatial element
174 public long ref; // ID of Comp
175 public int size; // Number of Prims in this Comp
176 public Comp(long r, int s) {
177 ref = r;
178 size = s;
179 }
180 }
181
182 public enum Pflag {
183 NOSP, POINT, LINE, AREA
184 }
185
186 public class Geom { // Geometric structure of feature
187 public Pflag prim; // Geometry type
188 public ArrayList<Prim> elems; // Ordered list of elements
189 public int outers; // Number of outers
190 public int inners; // Number of inners
191 public ArrayList<Comp> refs; // Ordered list of compounds
192 public double area; // Area of feature
193 public double length; // Length of feature
194 public Snode centre; // Centre of feature
195 public Geom(Pflag p) {
196 prim = p;
197 elems = new ArrayList<Prim>();
198 outers = inners = 0;
199 refs = new ArrayList<Comp>();
200 area = 0;
201 length = 0;
202 centre = new Snode();
203 }
204 }
205
206 public class Feature {
207 public Rflag reln; // Relationship status
208 public Geom geom; // Geometry data
209 public Obj type; // Feature type
210 public AttMap atts; // Feature attributes
211 public RelTab rels; // Related objects
212 public ObjMap objs; // Slave object attributes
213
214 Feature() {
215 reln = Rflag.UNKN;
216 geom = new Geom(Pflag.NOSP);
217 type = Obj.UNKOBJ;
218 atts = new AttMap();
219 rels = new RelTab();
220 objs = new ObjMap();
221 }
222 }
223
224 public NodeTab nodes;
225 public EdgeTab edges;
226
227 public FtrMap features;
228 public FtrTab index;
229
230 public long ref;
231 private Feature feature;
232 private Edge edge;
233
234 public S57map() {
235 nodes = new NodeTab(); // All nodes in map
236 edges = new EdgeTab(); // All edges in map
237 feature = new Feature(); // Current feature being built
238 features = new FtrMap(); // All features in map, grouped by type
239 index = new FtrTab(); // Feature look-up table
240 ref = 0x0000ffffffff0000L;// Compound reference generator
241 }
242
243 // S57 map building methods
244
245 public void newNode(long id, double lat, double lon, Nflag flag) {
246 nodes.put(id, new Snode(Math.toRadians(lat), Math.toRadians(lon), flag));
247 if (flag == Nflag.ANON) {
248 edge.nodes.add(id);
249 }
250 }
251
252 public void newNode(long id, double lat, double lon, double depth) {
253 nodes.put(id, new Dnode(Math.toRadians(lat), Math.toRadians(lon), depth));
254 }
255
256 public void newFeature(long id, Pflag p, long objl) {
257 feature = new Feature();
258 Obj obj = S57obj.decodeType(objl);
259 if (obj == Obj.BCNWTW)
260 obj = Obj.BCNLAT;
261 if (obj == Obj.BOYWTW)
262 obj = Obj.BOYLAT;
263 if (obj == Obj.C_AGGR)
264 feature.reln = Rflag.UNKN;
265 feature.geom = new Geom(p);
266 feature.type = obj;
267 if (obj != Obj.UNKOBJ) {
268 index.put(id, feature);
269 }
270 }
271
272 public void newObj(long id, int rind) {
273 Rflag r = Rflag.UNKN;
274 switch (rind) {
275 case 1:
276 r = Rflag.MASTER;
277 break;
278 case 2:
279 r = Rflag.SLAVE;
280 break;
281 case 3:
282 r = Rflag.UNKN;
283 break;
284 }
285 feature.rels.add(new Reln(id, r));
286 }
287
288 public void endFeature() {
289
290 }
291
292 public void newAtt(long attl, String atvl) {
293 Att att = S57att.decodeAttribute(attl);
294 AttVal<?> val = S57val.decodeValue(atvl, att);
295 feature.atts.put(att, val);
296 }
297
298 public void newPrim(long id, long ornt, long usag) {
299 feature.geom.elems.add(new Prim(id, (ornt != 2), (usag != 2)));
300 }
301
302 public void addConn(long id, int topi) {
303 if (topi == 1) {
304 edge.first = id;
305 } else {
306 edge.last = id;
307 }
308 }
309
310 public void newEdge(long id) {
311 edge = new Edge();
312 edges.put(id, edge);
313 }
314
315 public void endFile() {
316 for (long id : index.keySet()) {
317 Feature feature = index.get(id);
318 sortGeom(feature);
319 for (Reln reln : feature.rels) {
320 Feature rel = index.get(reln.id);
321 if (cmpGeoms(feature.geom, rel.geom)) {
322 switch (reln.reln) {
323 case SLAVE:
324 feature.reln = Rflag.MASTER;
325 break;
326 default:
327 feature.reln = Rflag.UNKN;
328 break;
329 }
330 rel.reln = reln.reln;
331 } else {
332 reln.reln = Rflag.UNKN;
333 }
334 }
335 }
336 for (long id : index.keySet()) {
337 Feature feature = index.get(id);
338 if (feature.reln == Rflag.UNKN) {
339 feature.reln = Rflag.MASTER;
340 }
341 if ((feature.type != Obj.UNKOBJ) && (feature.reln == Rflag.MASTER)) {
342 if (features.get(feature.type) == null) {
343 features.put(feature.type, new ArrayList<Feature>());
344 }
345 features.get(feature.type).add(feature);
346 }
347 }
348 for (long id : index.keySet()) {
349 Feature feature = index.get(id);
350 for (Reln reln : feature.rels) {
351 Feature rel = index.get(reln.id);
352 if (rel.reln == Rflag.SLAVE) {
353 if (feature.objs.get(rel.type) == null) {
354 feature.objs.put(rel.type, new ObjTab());
355 }
356 ObjTab tab = feature.objs.get(rel.type);
357 int ix = tab.size();
358 tab.put(ix, rel.atts);
359 }
360 }
361 }
362 }
363
364 // OSM map building methods
365
366 public void addNode(long id, double lat, double lon) {
367 Snode node = new Snode(Math.toRadians(lat), Math.toRadians(lon));
368 nodes.put(id, node);
369 feature = new Feature();
370 feature.reln = Rflag.UNKN;
371 feature.geom.prim = Pflag.POINT;
372 feature.geom.elems.add(new Prim(id));
373 edge = null;
374 }
375
376 public void addEdge(long id) {
377 feature = new Feature();
378 feature.reln = Rflag.UNKN;
379 feature.geom.prim = Pflag.LINE;
380 feature.geom.elems.add(new Prim(id));
381 edge = new Edge();
382 }
383
384 public void addToEdge(long node) {
385 if (edge.first == 0) {
386 edge.first = node;
387 nodes.get(node).flg = Nflag.CONN;
388 } else {
389 if (edge.last != 0) {
390 edge.nodes.add(edge.last);
391 }
392 edge.last = node;
393 }
394 }
395
396 public void addArea(long id) {
397 feature = new Feature();
398 feature.reln = Rflag.UNKN;
399 feature.geom.prim = Pflag.AREA;
400 edge = null;
401 }
402
403 public void addToArea(long id, boolean outer) {
404 feature.geom.elems.add(new Prim(id, outer));
405 }
406
407 public void addTag(String key, String val) {
408 feature.reln = Rflag.MASTER;
409 String subkeys[] = key.split(":");
410 if ((subkeys.length > 1) && subkeys[0].equals("seamark")) {
411 Obj obj = S57obj.enumType(subkeys[1]);
412 if ((subkeys.length > 2) && (obj != Obj.UNKOBJ)) {
413 int idx = 0;
414 Att att = Att.UNKATT;
415 try {
416 idx = Integer.parseInt(subkeys[2]);
417 if (subkeys.length == 4) {
418 att = s57.S57att.enumAttribute(subkeys[3], obj);
419 }
420 } catch (Exception e) {
421 att = S57att.enumAttribute(subkeys[2], obj);
422 }
423 ObjTab objs = feature.objs.get(obj);
424 if (objs == null) {
425 objs = new ObjTab();
426 feature.objs.put(obj, objs);
427 }
428 AttMap atts = objs.get(idx);
429 if (atts == null) {
430 atts = new AttMap();
431 objs.put(idx, atts);
432 }
433 AttVal<?> attval = S57val.convertValue(val, att);
434 if (attval.val != null)
435 atts.put(att, attval);
436 } else {
437 if (subkeys[1].equals("type")) {
438 obj = S57obj.enumType(val);
439 feature.type = obj;
440 ObjTab objs = feature.objs.get(obj);
441 if (objs == null) {
442 objs = new ObjTab();
443 feature.objs.put(obj, objs);
444 }
445 AttMap atts = objs.get(0);
446 if (atts == null) {
447 atts = new AttMap();
448 objs.put(0, atts);
449 }
450 } else {
451 Att att = S57att.enumAttribute(subkeys[1], Obj.UNKOBJ);
452 if (att != Att.UNKATT) {
453 AttVal<?> attval = S57val.convertValue(val, att);
454 if (attval.val != null)
455 feature.atts.put(att, attval);
456 }
457 }
458 }
459 }
460 }
461
462 public void tagsDone(long id) {
463 switch (feature.geom.prim) {
464 case POINT:
465 Snode node = nodes.get(id);
466 if (node.flg != Nflag.CONN) {
467 node.flg = Nflag.ISOL;
468 }
469 feature.geom.length = 0;
470 feature.geom.area = 0;
471 break;
472 case LINE:
473 edges.put(id, edge);
474 nodes.get(edge.first).flg = Nflag.CONN;
475 nodes.get(edge.last).flg = Nflag.CONN;
476 if (edge.first == edge.last) {
477 feature.geom.prim = Pflag.AREA;
478 }
479 sortGeom(feature);
480 feature.geom.length = calcLength(feature.geom);
481 if (feature.geom.prim == Pflag.AREA) {
482 feature.geom.area = calcArea(feature.geom);
483 } else {
484 feature.geom.area = 0;
485 }
486 break;
487 case AREA:
488 sortGeom(feature);
489 feature.geom.length = calcLength(feature.geom);
490 feature.geom.area = calcArea(feature.geom);
491 break;
492 default:
493 break;
494 }
495 if ((feature.type != Obj.UNKOBJ) && !((edge != null) && (edge.last == 0))) {
496 index.put(id, feature);
497 if (features.get(feature.type) == null) {
498 features.put(feature.type, new ArrayList<Feature>());
499 }
500 features.get(feature.type).add(feature);
501 feature.geom.centre = findCentroid(feature);
502 }
503 }
504
505 // Utility methods
506
507 public void sortGeom(Feature feature) {
508 Geom sort = new Geom(feature.geom.prim);
509 long first = 0;
510 long last = 0;
511 Comp comp = null;
512 boolean next = true;
513 if ((feature.geom.prim == Pflag.LINE) || (feature.geom.prim == Pflag.AREA)) {
514 int sweep = feature.geom.elems.size();
515 while (!feature.geom.elems.isEmpty()) {
516 Prim prim = feature.geom.elems.remove(0);
517 Edge edge = edges.get(prim.id);
518 if (next == true) {
519 next = false;
520 if (prim.forward) {
521 first = edge.first;
522 last = edge.last;
523 } else {
524 first = edge.last;
525 last = edge.first;
526 }
527 sort.elems.add(prim);
528 if (prim.outer) {
529 sort.outers++;
530 } else {
531 sort.inners++;
532 }
533 comp = new Comp(ref++, 1);
534 sort.refs.add(comp);
535 } else {
536 if (prim.forward) {
537 if (edge.first == last) {
538 sort.elems.add(prim);
539 last = edge.last;
540 comp.size++;
541 } else if (edge.last == first) {
542 sort.elems.add(0, prim);
543 first = edge.first;
544 comp.size++;
545 } else {
546 feature.geom.elems.add(prim);
547 }
548 } else {
549 if (edge.last == last) {
550 sort.elems.add(prim);
551 last = edge.first;
552 comp.size++;
553 } else if (edge.first == first) {
554 sort.elems.add(0, prim);
555 first = edge.last;
556 comp.size++;
557 } else {
558 feature.geom.elems.add(prim);
559 }
560 }
561 }
562 if (--sweep == 0) {
563 next = true;
564 sweep = feature.geom.elems.size();
565 }
566 }
567 if ((sort.prim == Pflag.LINE) && (sort.outers == 1) && (sort.inners == 0) && (first == last)) {
568 sort.prim = Pflag.AREA;
569 }
570 feature.geom = sort;
571 }
572 if (feature.geom.prim == Pflag.AREA) {
573 ArrayList<Prim> outers = new ArrayList<Prim>();
574 ArrayList<Prim> inners = new ArrayList<Prim>();
575 for (Prim prim : feature.geom.elems) {
576 if (prim.outer) {
577 outers.add(prim);
578 } else {
579 inners.add(prim);
580 }
581 }
582 ArrayList<Prim> sorting = outers.size() > 0 ? outers : inners;
583 ArrayList<Prim> closed = null;
584 sort = new Geom(feature.geom.prim);
585 sort.outers = feature.geom.outers;
586 sort.inners = feature.geom.inners;
587 sort.refs = feature.geom.refs;
588 next = true;
589 while (!sorting.isEmpty()) {
590 Prim prim = sorting.remove(0);
591 Edge edge = edges.get(prim.id);
592 if (next == true) {
593 next = false;
594 closed = new ArrayList<Prim>();
595 closed.add(prim);
596 if (prim.forward) {
597 first = edge.first;
598 last = edge.last;
599 } else {
600 first = edge.last;
601 last = edge.first;
602 }
603 } else {
604 if (prim.forward) {
605 if (edge.first == last) {
606 last = edge.last;
607 closed.add(prim);
608 } else {
609 sorting.add(0, prim);
610 next = true;
611 }
612 } else {
613 if (edge.last == last) {
614 last = edge.first;
615 closed.add(prim);
616 } else {
617 sorting.add(0, prim);
618 next = true;
619 }
620 }
621 }
622 if (first == last) {
623 sort.elems.addAll(closed);
624 next = true;
625 }
626 if (sorting.isEmpty() && sorting == outers) {
627 sorting = inners;
628 next = true;
629 }
630 }
631 feature.geom = sort;
632 }
633 }
634
635 public boolean cmpGeoms (Geom g1, Geom g2) {
636 return ((g1.prim == g2.prim) && (g1.outers == g2.outers) && (g1.inners == g2.inners) && (g1.elems.size() == g2.elems.size()));
637 }
638
639 public class EdgeIterator {
640 Edge edge;
641 boolean forward;
642 ListIterator<Long> it;
643
644 public EdgeIterator(Edge e, boolean dir) {
645 edge = e;
646 forward = dir;
647 it = null;
648 }
649
650 public boolean hasNext() {
651 return (edge != null);
652 }
653
654 public long nextRef() {
655 long ref = 0;
656 if (forward) {
657 if (it == null) {
658 ref = edge.first;
659 it = edge.nodes.listIterator();
660 } else {
661 if (it.hasNext()) {
662 ref = it.next();
663 } else {
664 ref = edge.last;
665 edge = null;
666 }
667 }
668 } else {
669 if (it == null) {
670 ref = edge.last;
671 it = edge.nodes.listIterator(edge.nodes.size());
672 } else {
673 if (it.hasPrevious()) {
674 ref = it.previous();
675 } else {
676 ref = edge.first;
677 edge = null;
678 }
679 }
680 }
681 return ref;
682 }
683
684 public Snode next() {
685 return nodes.get(nextRef());
686 }
687 }
688
689 public class GeomIterator {
690 Geom geom;
691 Prim prim;
692 EdgeIterator eit;
693 ListIterator<S57map.Prim> ite;
694 ListIterator<Comp> itc;
695 Comp comp;
696 int ec;
697 long lastref;
698
699 public GeomIterator(Geom g) {
700 geom = g;
701 lastref = 0;
702 ite = geom.elems.listIterator();
703 itc = geom.refs.listIterator();
704 }
705
706 public boolean hasComp() {
707 return (itc.hasNext());
708 }
709
710 public long nextComp() {
711 comp = itc.next();
712 ec = comp.size;
713 lastref = 0;
714 return comp.ref;
715 }
716
717 public boolean hasEdge() {
718 return (ec > 0) && ite.hasNext();
719 }
720
721 public long nextEdge() {
722 prim = ite.next();
723 eit = new EdgeIterator(edges.get(prim.id), prim.forward);
724 ec--;
725 return prim.id;
726 }
727
728 public boolean hasNode() {
729 return (eit.hasNext());
730 }
731
732 public long nextRef(boolean all) {
733 long ref = eit.nextRef();
734 if (!all && (ref == lastref)) {
735 ref = eit.nextRef();
736 }
737 lastref = ref;
738 return ref;
739 }
740
741 public long nextRef() {
742 return nextRef(false);
743 }
744
745 public Snode next() {
746 return nodes.get(nextRef());
747 }
748 }
749
750 double signedArea(Geom geom) {
751 Snode node;
752 double lat, lon, llon, llat;
753 lat = lon = llon = llat = 0;
754 double sigma = 0;
755 GeomIterator git = new GeomIterator(geom);
756 if (git.hasComp()) {
757 git.nextComp();
758 while (git.hasEdge()) {
759 git.nextEdge();
760 while (git.hasNode()) {
761 llon = lon;
762 llat = lat;
763 node = git.next();
764 lat = node.lat;
765 lon = node.lon;
766 sigma += (lon * Math.sin(llat)) - (llon * Math.sin(lat));
767 }
768 }
769 }
770 return sigma / 2.0;
771 }
772
773 public boolean handOfArea(Geom geom) {
774 return (signedArea(geom) < 0);
775 }
776
777 public double calcArea(Geom geom) {
778 return Math.abs(signedArea(geom)) * 3444 * 3444;
779 }
780
781 public double calcLength(Geom geom) {
782 Snode node;
783 double lat, lon, llon, llat;
784 lat = lon = llon = llat = 0;
785 double sigma = 0;
786 boolean first = true;
787 GeomIterator git = new GeomIterator(geom);
788 while (git.hasComp()) {
789 git.nextComp();
790 while (git.hasEdge()) {
791 git.nextEdge();
792 while (git.hasNode()) {
793 node = git.next();
794 if (first) {
795 first = false;
796 lat = node.lat;
797 lon = node.lon;
798 } else {
799 llat = lat;
800 llon = lon;
801 lat = node.lat;
802 lon = node.lon;
803 sigma += Math.acos(Math.sin(lat) * Math.sin(llat) + Math.cos(lat) * Math.cos(llat) * Math.cos(llon - lon));
804 }
805 }
806 }
807 }
808 return sigma * 3444;
809 }
810
811 public Snode findCentroid(Feature feature) {
812 double lat, lon, slat, slon, llat, llon;
813 llat = llon = lat = lon = slat = slon = 0;
814 double sarc = 0;
815 boolean first = true;
816 switch (feature.geom.prim) {
817 case POINT:
818 return nodes.get(feature.geom.elems.get(0).id);
819 case LINE:
820 GeomIterator git = new GeomIterator(feature.geom);
821 while (git.hasComp()) {
822 git.nextComp();
823 while (git.hasEdge()) {
824 git.nextEdge();
825 while (git.hasNode()) {
826 Snode node = git.next();
827 lat = node.lat;
828 lon = node.lon;
829 if (first) {
830 first = false;
831 } else {
832 sarc += (Math.acos(Math.cos(lon - llon) * Math.cos(lat - llat)));
833 }
834 llat = lat;
835 llon = lon;
836 }
837 }
838 }
839 double harc = sarc / 2;
840 sarc = 0;
841 first = true;
842 git = new GeomIterator(feature.geom);
843 while (git.hasComp()) {
844 git.nextComp();
845 while (git.hasEdge()) {
846 git.nextEdge();
847 while (git.hasNode()) {
848 Snode node = git.next();
849 lat = node.lat;
850 lon = node.lon;
851 if (first) {
852 first = false;
853 } else {
854 sarc = (Math.acos(Math.cos(lon - llon) * Math.cos(lat - llat)));
855 if (sarc > harc)
856 break;
857 }
858 harc -= sarc;
859 llat = lat;
860 llon = lon;
861 }
862 }
863 }
864 return new Snode(llat + ((lat - llat) * harc / sarc), llon + ((lon - llon) * harc / sarc));
865 case AREA:
866 git = new GeomIterator(feature.geom);
867 while (git.hasComp()) {
868 git.nextComp();
869 while (git.hasEdge()) {
870 git.nextEdge();
871 while (git.hasNode()) {
872 Snode node = git.next();
873 lat = node.lat;
874 lon = node.lon;
875 if (first) {
876 first = false;
877 } else {
878 double arc = (Math.acos(Math.cos(lon - llon) * Math.cos(lat - llat)));
879 slat += ((lat + llat) / 2 * arc);
880 slon += ((lon + llon) / 2 * arc);
881 sarc += arc;
882 }
883 llon = lon;
884 llat = lat;
885 }
886 }
887 }
888 return new Snode((sarc > 0.0 ? slat / sarc : 0.0), (sarc > 0.0 ? slon / sarc : 0.0));
889 default:
890 }
891 return null;
892 }
893
894}
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