Subdivision Object

Attention: Cheetah3D 2.0 added the Subdivision modifier object which is now the prefered technic for using subdivision surfaces. But the Subdivision creator object will be maintained for backward compatibility.

The subdivision object allows you to take a simple polygon object and smooth its surfaces by exponentially increasing the number of polygons the shape is made from. It is functionally the same as the subdivide tool, although the subdivision object is a creator object, meaning that you place it into your scene, and drop a polygon objects inside it - this allows you to modify the original polygon object and see those changes reflected in the subdivided result. In combination with the parametric polygonobjects, this gives you a lot of freedom and power.

In the example above, you can see that the first box is a simple parametric polygon object. The second and third items are subdivision objects, each containing the same box as in the first - note how the shape of the box is smoothed by increasing the number of polygons. In the last subdivision object, the Iterations property has been increased to 3.

Cheetah3D offers two different subdivision schemes which both supports creases. The first is the classic Catmull-Clark subdivison scheme which most other 3D modelers support too. But the Catmull-Clark subdivision scheme has a handicap. It performs very well on quads but if there are triangles in the mesh artifacts can appear. The Stam-Loop scheme on the other side is an advanced subdivison scheme which uses the best properties from the Catmull-Clark and the Loop subdivison scheme. It therefore behaves much better on mixed meshes which include both quads and triangles. See the pictures below for a better understanding.


The original mesh which consists of triangles and quads.


The left image uses the classic Catmull-Clark subdivision scheme the right the Stam-Loop scheme The Catmull-Clark scheme creates ugly artifacts at the corner which is build up with triangles. The Stam-Loop scheme on the other side looks as one would expect.

Attention: The subdivision object will produce objects with very many polygons, especially when the Iterations property is increased. Take care not to overload your computer by increasing Iterations too high. 2 or 3 is often sufficient for good quality renders.

Tips:

  • When you use the subdivision object for modeling it could happen that points or polygons of the control mesh are hidden by the subdivided mesh. It is then impossible to select these points. The easiest way to select these points is to deactivate the subdivision object temporarily. This can be done by unchecking the "create" property of the subdivision objects mode tag.
    The deactivation of the subdivision object can be even performed by the " Create parent object On/Off" hotkey. When you've defined this hotkey in the preferences window it is possible to deactivate the parent object (in our case the subdivision object) when we are currently editing the control mesh.


The point of the control mesh in the upper right is hidden by the subdivision mesh. Deactivating the subdivision object by
unchecking the "create" property of the subdivision objects mode tag makes the point accessible.

  • The isoparamter mode of the "editor shading" property of the mode tag is also available in the subdivison object. This mode highlights the edges of the original control mesh.

Usage
To use the subdivision object you just drag and drop a polygon object into a subdivision object (as in the example above).

Properties

  • interations: Determines how many times to subdivide the surface of the child polygon objects. Defaults to 2.
  • scheme: Controls what sort of subdivision scheme is used. Catmull-Clark is the default, but you can also use the Stam-Loop scheme.

© 2001-2010 Martin Wengenmayer. All rights reserved.