4.4.2 Hole Determination Based Upon Overall Tree Structure
In this method a more advanced hole generator approach is used whereby holes are created at the intersection of big branches. The first potential place is the trunk and first branch intersection. The further the branching is from the trunk the less reason for a highly detailed model, therefore there should be a limit, and intersections between small branches should not generate holes and cracks. Another good position for possible holes could be the beginning of the roots whereby a hole is determined in an area where most of the vertices angles are low also in places where the roots meet the trunk’s surface.
Now that I have described the tools and two possible methods for hole detection I will provide the necessary steps for this process. The proposed process of hole generation is based on 3d studio max 9 work flow and tools, but could be easily implemented in any other 3d modeling application or created as a stand alone solution. For the sake of simplicity random vertices on a polygonal plane will be used, instead of vertices with low angular levels in tree trunk model.
The first step in hole generation is to select a candidate vertices group, which should form a hole. After the selection is done a chamfer tool is applied. The value which describes the distances where new vertices are created, could be half of an average edge length of selected vertices’. The next step would be to connect newly created vertices via the chamfer tool. The connection tool creates new edges between newly created vertices. Edge selection is converted to a polygon selection. See figure 33 where it describes the fourth step.
Fig 33. Proposals visualization.
Fig 33.first four steps in hole creation. The red dots represent selected vertices, red lines selected edges, and red shaded area represent selected polygons.
As Figure 33 shows the resulting polygon selection is not accurate. This is due to the fact that the edge selection conversion to a polygonal selection includes all neighboring
polygons. Polygonal selection should be shrunken to get the desired result.
Fig 34. Proposals visualization.
This is shown in Figure 34. The next step is to erase all selected polygons, and select the remaining edge outline and conduct an edge extrusion. The last step shown in Figure 34 represents a subdivision algorithm applied on a mesh.
The subdivision algorithm not only generates more detailed mesh structure, but also softens the edges of it. The steps I have described are rather easy to perform due to the ability of 3d studio max to remember the last used selection and convert vertices selections to edge or polygon selections. This process should be possible in any 3d modeling software, but it might include a different order of steps, or additional steps required to achieve the same result.
Figures 33 and 34 show steps which are very easily preformed manually. But the steps are also simple enough so that the actions could be automated. To manually create a hole as shown in Figures 33 and 34 it took around 5 minutes. But if a real trunk model was used with high mesh density and many holes to generate, this process could be very long.
My recommendations if implemented would decrease the amount of time involved in current tree generation.
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