Creating/Extending a Web (RS3)

Unfortunately, Defeat3d's tool is exclusively for OSRS.

I have been trying to extend or create a Web for several hours now, and still don't have a grasp of what exactly a Bidirectional Edge is, how it relates to the Web or even to a CoordinateVertex, or how a coordinate's isReachable affects webwalking. And many other things besides.

I and many future coders here would appreciate a conceptual explanation and an example of these things when the default web fails us.

My futile attempts at creating a web:

Code (Text):

1.  
2. private List<Coordinate> list;
3. private Web web;
4. private Collection<WebVertex> webList = new ArrayList<WebVertex>();
5.  
6. public void someMethod()
7. {
8.         Area area = new Area.Polygonal(new Coordinate[]
9.                 {
10.                 new Coordinate(2779,2999,0),
11.                 new Coordinate(2774,3011,0),
12.                 new Coordinate(2870,3038,0),
13.                 new Coordinate(2875,3016,0)
14.                 });
15.         list = area.getCoordinates();
16.      
17.         for(Coordinate c : list)
18.         {
19.             CoordinateVertex v = new CoordinateVertex(c);
20.             v.addBidirectionalEdge(new CoordinateVertex(c.derive(1, 0)));
21.             v.addBidirectionalEdge(new CoordinateVertex(c.derive(0, 1)));
22.             v.addBidirectionalEdge(new CoordinateVertex(c.derive(-1, 0)));
23.             v.addBidirectionalEdge(new CoordinateVertex(c.derive(0, -1)));
24.             webList.add(v);
25.         }
26.         web = Traversal.getDefaultWeb();
27.         web.addVertices(webList);
28. }
29.  
30.     @Override
31.     public void onLoop()
32.     {
33.         Execution.delayUntil(() -> web.getPathBuilder().buildTo(Data.OBELISK).step(true));
34.         stop();
35.     }
36. // results in a NullPointer, most likely because the path specified by buildTo doesn't exist.