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.

max hole

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.

max hole

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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You can visit my web page here

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Ok so I was looking around in flickr for some examples of a situations where automatrick tree generator is not suficient, and i fund lots of good pictures. Some depict tree holes, while others depict tree roots or other parts. The funny thing is that I contacted flicker users who uploaded pictures, and asked theyr permision to use images in this blog,. … guess what 100% of people who replyed to me sead ok… that was a nice surprice actualy. So here we go: flickr-trees

please click on it to enelarge… (i increased contrast in moust of images, i hope authors will not get too angry, its all about showing tree details, not art… well who knows about that :) and if there are any erors wiyh titles names or links, write me, it will be corrected.)

credits:

1. Tree with hole through it, Martin LaBar / Martin LaBar, http://www.flickr.com/people/martinlabar/

2. Tree Hole, Cryodigital, http://www.flickr.com/people/cryodigital/

3. Tree Hole Entry, Minnie Wong, http://www.flickr.com/people/26133907@N00/

4. Tree and hole ,Adventurer Dustin Holmes / Dustin Holmes, http://www.flickr.com/people/dustinholmes/

5. Tree holes, Opa Schoch / Shok the German, http://www.flickr.com/people/opaschoch/

6. Hole in the Tree, Kent Sandvik, http://www.flickr.com/people/kentsandvik/

7. Tree with Hole, brents pix’s, http://www.flickr.com/people/brentspix/

8. Baobab tree with a hole through its trunk, tommyimages_com’s, http://www.flickr.com/people/cuba_photos/

9. Hole-y Tree, Kuzeyli48′s, http://www.flickr.com/people/21915247@N07/

and, not saying that its best or anything like that, my manualy hand modeled tree…

medis / tree

and a wiki entry on a matter here :

http://en.wikipedia.org/wiki/Tree_hollow

and some copy paste from this article: (aka interesting fackts (if we trust wiki :) ) )

A tree hollow or tree hole is a semi-enclosed cavity which has naturally formed in the trunk or branch of a tree.

Hollows may form as the result of physiological stress from natural forces causing the excavating and exposure of the heartwood. Forces including wind, fire, heat, lightning, rain, attack from insects (such as termites or beetles), bacteria, or fungi. Also, trees may self-prune, dropping lower branches as they reach maturity, exposing the area where the branch was attached. Many animals further develop the hollows using using instruments such as their beak, teeth or claws.

In Australia, 304 vertebrate species are known to use tree hollows in Australia: 29 amphibians, 78 reptiles, 111 birds, 86 mammals.[2] Approximately 100 of these are now rare, threatened or near-threatened on Australian State or Commonwealth legislation, in part because of the removal of hollow-bearing trees[8][1].

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You can visit my web page here

dont like english? u can (try) readig it in lithuanian or anny other language here! alternative, has no lithuanian :(

4.3 Hole Generation

Overview: The Origin of “Holes” in Trees

It is rare to find a perfect tree in real life usually the older the tree the more defects it will have. Holes are a common attribute of trees found in the wild as well as trees planted by humans. Usually the holes are not that big and sometimes trees have much bigger empty parts inside the trunk or in big branches. The water collects there and makes a perfect situation for rotting. Also fungus or other animals make use of such holes, usually making them become bigger and bigger. Holes can appear as a result of humidity and dead leaves, which remain in same place for a long period of time. Holes are usually noticeable in tree “forks” this means where the trunk separates and two or more steams grow. This is evident in the connections of big branches, cracks and other complicated shapes of trunks. Usually the tree does not die just from rotting, but the rotting could destroy water circulation and that could lead to the long death of a tree which could take many years. If the wind tears a branch off or if other animals or insects injure the outer layers of tree, the fungus and other kind of bacteria start to live in these places, and that makes the tree rotten (Tree Holes).

Regarding the 3d generation of a hole it should begin by determining where are possible locations for a hole in a tree stem. Detection of possible locations could be done by determining where the trunk surface is not planar. The reason, is that holes in a trunk appear in positions where a tree is injured, or where the tree’s architecture is week. There are many biological reasons for a hole’s appearance, therefore there could be many solutions. So far I have described what a hole in a tree trunk is and I have also gone into details regarding how a hole appearance can be a result of a very old tree trunk injury. In the next section I present tools used as well as two proposals for an automatic hole generation tool which detects the best position of a hole utilizing two possible methods. The first method detects a possible hole’s position based upon a trees surface and where conditions are suitable for rotting to occur. The second method has more to do with the overall structure of a tree.

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some pictures from tiergarten in berlin:

tree holes

you can also wisit my portfolio.
dont like english? u can (try) readig it in lithuanian or anny other language here! alternative, has no lithuanian :(
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