here some tools will be presented which are in 3dmax. the same tools are probably in all 3d modeling programs but sins i am familiar with max, i will kind of talk in its terms.
In order to describe this aspect of hole generation as part of a proposal for an automatic tree generator it is important to introduce some tools related to this process.
These tools are available in almost all 3d modeling applications and are called insert polygon, connect, extrude and chamfer.
The Insert polygon tool shrinks a selected polygon along its plane, and adds four additional polygons. Using this strategy, there is an original polygon as a boundary, and five new polygons inside. The middle one has exactly the same outline as first one, onto which we applied the tool, and others are made by connecting edges of the original polygon and new one which is smaller. This tool works not only with quadrilaterals, but also with any given polygons or polygon groups. To better understand the way this tool works please look at figure 29
Fig 29. screenshots from 3d studio max.
The Chamfer tool works with vertices. This tool can be applied on a selected single vertex or multiple vertices. In order to understand the chamfer tool, imagine a situation where one vertex is connected to four other vertices by four edges. After the chamfer tool is applied four new vertices are created on edges connecting the first original vertex to its surrounding vertices’s. The distance is always specified by the user and then the newly created vertices are connected with new edges. The original vertex which was selected in a first place is
erased. For clarification see figure 30.
Fig 30. screenshots from 3d studio max.
fig 30. shows selected 4 vertices (top) and resulting mesh structure after chamfer operation (bottom)
The Connect tool connects selected vertices by creating new edges. The Extrude (Landrenau 2005) is a tool which moves a selected polygon or polygons along a normal and creates new polygons that form the sides of the extrusion, connecting the selection to the object. For clarification see figure 31.
Fig 31. Picture taken from: Eric Landrenau. 2005. Crystal-Like Geometric Modeling. Thesis of Master of Science. Texas A&M University
Now that you are familiar with the tools necessary for a proposed automatic hole generator, what follows will be two approaches for the detection of where a hole a could be generated. Once this is described the proposed steps for the generation of a hole will be outlined.