While getting bigger some parts of trees tend to connect in between and become as one part. It is very likely to happened in a base of trunk and in root level under earth. Sometimes it happens to the double trunks. Some trees are goring as two, and become as one. This feature might be not so relevant for realistic trees, but it sure is a good addition to more interesting and artistically more “advanced” trees.

Possible meatball usage in tree trunk generation

Another possible way of tree trunk detalization could possibly be done by meatballs usage in the trunk surface generation.

In most of current day available 3d packages, metabals (aka: inplicit surfaces blob mesh) are common modeling technique. Also, we are not limited by using metabals, as a controllers for newly created “blobby” looking mesh, but we also can use already made 3d model – which would act as a matrix of metabals. Usually metabal creation tool would interpret each vertex of the model as a controlling metabal, and in such way we would use reference model of lower 3d detail, to create metaball surface.

edges of hole in blobmesh

roots with blobmesh.

top row shows edges and polygons. 1 input mesh, 2 blobmesh 3 multires (mesh optimization) 4 meshsmooth (subdivision surface)

expected advantages

If we would take our generated tree trunk surface, and use it as a reference model for metabals creation, we would achieve automatic metalization, of surface which would follow general surface outlines. The ideal solution would be to get easy control over each metaballs threshold values. usually metaball tools lets us to set threshold values only to all set of metabals, and restrict us of having different values for each metabal. it would be very beneficial to overcome this limit. Also would be nice to set different resulting mesh density settings for each metaball. Currently the setting works for all metabals which are in a same set. That means if one sets certain value of mesh density average distances from vertexes in all resulting mesh will be almost same. In some case we don’t need high detail inside of tree, or some areas which are plain and do not have much variance in surface.

This is not currently available feature of metabals and would require further investigation, probably new metaball creation algorithms too.

The “work around” in case of making additional polygons in flat areas, which are not needed would be after creation of surface, to apply a mesh optimization algorithm, which would try to reduce polygons where they are not needed. The bad thing about this “work around” is we spend double time generating unnecessary polygons and then trying to remove them. Also in some cases it is good to have high detailed mesh even in flat areas if we are considering to apply displacement maps at the render time or before.

The corners of holes in a tree would look very good if used metaballs technique, it would create an inner surface for a tree, and the corners of the holes would look rounded, not sharp, which is how the natural tree holes look like

expected disadvantages

common disadvantages of current metaballs algorithms is creation of so called bad mesh topology. Also if there is a polygon in a mesh, which vertex distances are much bigger then the average of the models vertex distances, the resulting surface after applying metaball operation would result a hole in a mesh at the given polygon.

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