4.2.2 Step Two: Circle Creation

As it has been already mentioned a tree trunk model is usually based on simple cylindrical shapes. In order to create a cylinder there must be a central axis, and a circle of a certain radius which would define its outer surface boundaries. Therefore the next step to creating a trunk model is to create circles, whose centers’ have positions where by each point is in line with a guiding curve as discussed above. As each point in this curve has different positions in space, so will the resulting circles.

4.2.3 Step Three: Shape Refinement Curves

The third step in the generation of a tree trunk is to copy a guiding curve. The number of copies can be defined by the user. In example shown in Figure 28 copies have already been made. Copied curves here will be called shape refinement curves. After copying them the shape refinement curves should be off set. Off set values are also definable by the user but the default value should be the same as the radius of circle which was created in step two. The refinement curves should be distributed equally along the circle’s perimeter. For

clarification please look at Figure 28 step 3

4.2.4 Step Four: Shape Refinement Circles

Step four in the trunk generation process is to create shape refinement circles which are generated for each point along the surface of the refinement curves. The radius of the refinement circles are definable by the user yet the default value is one third of first circles’ radius.

4.2.5 Step Five: Outline Generation

In step five the generator deletes all splines since they are no longer needed. Then each circle is combined with refinement circles and all intersections are removed leaving behind only an outline. At this stage the method takes advantage of Boolean operations (see Chapter 3 for further explanation). The shapes are then added together and intersecting parts are removed. The end result being an outline of the circle and refinement circles. For clarification of this step please look at Figure 28 step5.

4.2.6 Step Six: Surface Generation

The final step in the trunk generation process would be the creation of the trunk’s surface. In order to create a surface we need to know where each vertex of our polygon mesh will be located. To obtain this information we first will reduce the quality of the outlines generated in step 5. This means the algorithm for trunk generation has to approximate the outline shapes by describing curves using a pre- defined number of points. This means we would have a list of point positions, which define locations of vertices which could then construct a mesh model of the trunk. For clarification please refer to Figure 28.

So far improvements to overall trunk generation have been presented. What follows in this section will introduce another recommendation to do with the biological origins of a “hole” in a tree trunk and a proposal for this to be included in an automatic tree generator. As a part of this explanation possible tools for this approach will be outlined.

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