4.4 Recommended Methods for Hole Generation
Two methods will be proposed to determine holes position in a tree trunk.
4.4.1 Hole’s Position Based Upon Complex Trunk Surface
This proposed method for the generation of a hole begins by creating a list of all vertices of a trunk model. In a standard 3d model each vertex is connected to the other vertex by an edge. Typically one vertex has three or four connections, meaning three or four edges are connecting it to the other vertex. If we have a list of vertexes and their spacial positions in a 3d coordinate system, we can calculate angles that makes those connections. In order to know the angle we have first to have two edges that directly connect to the vertex we are discussing. Now following the same procedure we can make a list in which all vertices would be sorted out by their edge angular values. The lowest values are a good candidate for the position of a crack in a tree surface or hole.
As figure 32 illustrates the angles are measured on the outside surface of a trunk. In this example angles are calculated only between horizontal edges and not vertical for sake of simplicity. A fully functional approach should be able to handle vertices which have only 3 or another irregular number of connections as opposed to four connections.
Fig 32. Proposals visualization.
The list of vertices and their edges value are sorted, according to their angular value. The lower the value the better a candidate for a hole vertex. In the example described in Figure 32, vertices 5 and 14 have the lowest angular values.
The next step is to determine groups of vertices with low angular values. According to this solution the closer two vertices with low angular values are the better candidates they are for a hole. Priority of a proposed algorithm would be not isolated vertices but instead groups of vertices with low angular values. This method would be one way to determine a possible crack and hole start position.
There are other situations when holes appear, and different methods are still to be found to determine the position of holes. The next section focuses not only on groups of vertices for hole generation but also on the location of these holes and where they might be more appropriate.
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