OOF2: The Manual

Details

Description

FixIllegal is a SkeletonModifier that fixes illegal Skeleton Elements.

Excluding paranormal alien interventions, illegal elements are only generated by moving Nodes manually with the Move Nodes toolbox. Illegal elements are BAD, so they should be removed immediately.

FixIllegal fixes an Element by moving one or more of its Nodes to the average position of its neighboring Nodes In many cases, it is sufficient to fix an Element by applying this smoothing procedure to the offending Nodes, namely those Nodes located at corners that subtend interior angles greater than 180 degrees or less than 0 degrees (for quadrilaterals, illegal elements include those that have non-convex geometries). However, this smoothing procedure may not work when the corner angle is very close to zero. In this case, the Nodes at other corners should be moved as well. Each move is ultimately accepted or rejected solely by whether or not it reduces the number of illegal Elements in the vicinity of the Node.

Figure 6.77 shows a Skeleton that gives a pretty good representation of the underlying Microstructure. Figure 6.78 shows the Skeleton after a Node has been moved to create two illegal Elements (shown in red). The node motion is indicated by the arrow in Figure 6.77. Figure 6.79 shows the Skeleton after FixIllegal has been applied. Notice that although there are no illegal Elements, the Skeleton is no longer such a good representation of the Microstructure. This is because FixIllegal is a brutal technique: it pays no attention to Element homogeneity or shape energy.

Figure 6.77. A Legal Skeleton

Figure 6.78. An Illegal Skeleton

Figure 6.79. A Rehabilitated Skeleton

On one pass through the Skeleton, FixIllegal attempts to move each Node of the troublesome element once, choosing the Nodes in a random order. It may not be successful on the first pass, so it repeats the process until there are no more illegal Elements. If it fails to remove all the illegal Elements after a fixed number of iterations,^[28] it will quit trying and notify the user.